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HCCI ENGINE
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Dept. Of Mechanical Engg, Dr . SMCE, Bengaluru . 2013
ABSTRACT
In the context of environmental restrictions and sustainable development, pollution standards have
become more and more stringent. The design of most fuel efficient and environmental friendly
internal combustion engine so as to meet the future emission standards is currently one of the main
goals of engine researchers. Homogeneous Charge Compression Ignition (HCCI) combustion has the
potential to be highly efficient and to produce low emissions. HCCI engines can have efficiencies as
high as compression-ignition direct-injection (CIDI) engines (an advanced version of the commonly
known diesel engine), while producing ultra-low oxides of nitrogen (NOx) and particulate matter
(PM) emissions. HCCI engines can operate on gasoline, diesel fuel, and most alternative fuels. HCCI
represents the next major step beyond high efficiency CIDI and spark-ignition, direct-injection
(SIDI) engines for use in transportation vehicles. In some regards, HCCI engines incorporate the best
features of both spark ignition (SI) gasoline engines and CIDI engines. Like an SI engine, the charge
is well mixed which minimizes particulate emissions, and like a CIDI engine it is compression
ignited and has no throttling losses, which leads to high efficiency. However, unlike either of these
conventional engines, combustion occurs simultaneously throughout the cylinder volume rather than
in a flame front. This paper reviews the technology involved in HCCI engine, and its merits and
demerits. The challenges encountered and recent developments in HCCI engine are also discussed in
this paper.
CONTENTS
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1 Introduction 1 2 History 3 3 What is HCCI? 5
o Why HCCI? 6 4 Fundamentals & Requirements Of HCCI 6 5 Operation 9
o 5.1 Methods 9o 5.2 Advantages 9o 5.3 Disadvantages 10o 5.4 Control 10
5.4.1 Need for control 10 5.4.2 Variable compression ratio 10 5.4.3 Variable induction temperature 11 5.4.4 Variable exhaust gas percentage 11 5.4.5 Variable valve actuation 11 5.4.6 Variable fuel ignition quality 12 5.4.7 Direct Injection: PCCI or PPCI Combustion 12
o 5.5 High peak pressures and heat release rates 12o 5.6 Power 13o 5.7 Emissions 13o 5.8 Difference from Knock 14o 5.9 Simulation of HCCI Engines 14
6 Prototypes 14 7 Other Applications of HCCI Research 15 8 Challenges For HCCI 15
o 8.1 Controlling Ignition Timing 16o 8.2 Extending The Operating Range 16o 8.3 Cold-Start Capability 17o 8.4 Variable Ignition Timing 17
9 Recent Developments In HCCI 19 10 Conclusion 19 References 20
http://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Introductionhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Historyhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Historyhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Operationhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Methodshttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Advantageshttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Disadvantageshttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Controlhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Controlhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Variable_compression_ratiohttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Variable_induction_temperaturehttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Variable_exhaust_gas_percentagehttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Variable_valve_actuationhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Variable_fuel_ignition_qualityhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Direct_Injection:_PCCI_or_PPCI_Combustionhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#High_peak_pressures_and_heat_release_rateshttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#High_peak_pressures_and_heat_release_rateshttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Powerhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Emissionshttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Difference_from_Knockhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Simulation_of_HCCI_Engineshttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Prototypeshttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Other_Applications_of_HCCI_Researchhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Other_Applications_of_HCCI_Researchhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Other_Applications_of_HCCI_Researchhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Prototypeshttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Simulation_of_HCCI_Engineshttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Difference_from_Knockhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Emissionshttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Powerhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#High_peak_pressures_and_heat_release_rateshttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Direct_Injection:_PCCI_or_PPCI_Combustionhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Variable_fuel_ignition_qualityhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Variable_valve_actuationhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Variable_exhaust_gas_percentagehttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Variable_induction_temperaturehttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Variable_compression_ratiohttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Controlhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Disadvantageshttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Advantageshttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Methodshttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Operationhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Historyhttp://en.wikipedia.org/wiki/Homogeneous_charge_compression_ignition#Introduction -
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List of Figures
Fig.1 Side and Frontal views of the Nissan MK 2.5 Liter Engine. 3
Fig.2 Homogeneous Charge Compression Ignition. 5
Fig.3 Shows the concept of HCCI engine. 7
Fig.4 The temperature history in K for is preventative ODT 7simulation. The vertical Axis corresponds to a slice through the
cylinder. Ignition occurs following compression, heating and turbulent mixing.
Fig.5 This pressure trace shows the differences between completely 7homogeneous mixtures and mixtures with small-scale inhomogeneities.
Fig.6 Shows the emission characteristics. 13
Fig.7 shows a relation between Temperature vs Crank Angle & 15
Pressure vs Crank Angle during combustion process of HCCI engine.
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1.INTRODUCTIONEnvironmental protection is a huge growth market for the future. In the years ahead, green
technologies that help improve energy efficiency or reduce emissions will be important growth. With
the advent of increasingly stringent fuel consumption and emissions standards, engine manufacturers
face the challenging task of delivering conventional vehicles that abide by these regulations. HCCI
combustion has the potential to be highly efficient and to produce low emissions. HCCI engines can
have efficiencies as high as compression-ignition, direct-injection (CIDI) engines (an advanced
version of the commonly known diesel engine), while producing ultra-low oxides of nitrogen (NOx)
and particulate matter (PM) emissions. HCCI engines can operate on gasoline, diesel fuel, and most
alternative fuels. While HCCI has been demonstrated and known for quite some time, only the recent
advent of electronic sensors and controls have made HCCI engines a potential practical reality.
HCCI represents the next major step beyond high efficiency CIDI and spark-ignition, direct-
injection (SIDI) engines for use in transportation vehicles. In some regards, HCCI enginesincorporate the best features of both spark ignition (SI) gasoline engines and CIDI engines. Like an
SI engine, the charge is well mixed which minimizes particulate emissions, and like a CIDI engine it
is compression ignited and has no throttling losses, which leads to high efficiency. However, unlike
either of these conventional engines, combustion occurs simultaneously throughout the cylinder
volume rather than in a flame front. HCCI engines have the potential to be lower cost than CIDI
engines because they would likely use a lower pressure fuel-injection system. The emission control
systems for HCCI engines have the potential to be less costly and less dependent on scarce precious
metals than either SI or CIDI engines. HCCI engines might be commercialized in light-duty
passenger vehicles and as much as a half-million barrels of primary oil per day may be saved.
HCCI is potentially applicable to both light and heavy-duty engines. Light-duty HCCI engines can
run on gasoline and have the potential to match or exceed the efficiency of diesel-fuelled CIDI
engines, without the major challenge of NOx and PM emission control or impacting fuel-refining
capability. For heavy-duty vehicles, successful development of the diesel-fuelled HCCI engine is an
important alternative strategy in the event that CIDI engines cannot achieve future NOx and PM
emissions standards.
In fact, HCCI technology could be scaled to virtually every size-class of transportation engines from
small motorcycle to large ship engines. HCCI is also applicable to piston engines used outside the
transportation sector such as those used for electrical power generation and pipeline pumping. HCCIengines are particularly well suited to series hybrid vehicle applications because the engine can be
optimized for operation over a more limited range of speeds and loads compared to primary engines
used with conventional vehicles. Use of HCCI engines in series hybrid vehicles could further
leverage the benefits of HCCI to create highly fuel-efficient vehicles.
Japan and European countries have aggressive research and development (R&D) programs in HCCI,
including both public- and private-sector components. Many of the leading HCCI developments to
date have come from these countries. In fact, two engines are already in production in Japan that use
HCCI during a portion of their operating range: Nissan is producing a light truck engine that uses
intermittent HCCI operation and diesel fuel, and Honda is producing a 2-stroke cycle gasoline engineusing HCCI for motorcycles. HCCI engines cannot be ignored. HCCI combustion is achieved by
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controlling the temperature, pressure, and composition of the fuel and air mixture so that it
spontaneously ignites in the engine. This control system is fundamentally more challenging than
using a spark plug or fuel injector to determine ignition timing as used in SI and CIDI engines,
respectively. The recent advent of electronic engine controls has enabled consideration of HCCI
combustion for application to commercial engines. Even so, several technical barriers must beovercome to make HCCI engines applicable to a wide range of vehicles and viable for high volume
production. Significant challenges include: Controlling Ignition Timing and Burn Rate over a
Range of Engine Speeds and Loads Extending the Operating Range of HCCI to High Engine Loads
Cold-Starts and transient response with HCCI Engines Minimizing Hydrocarbon and Carbon
Monoxide Emissions
Controlling the operation of an HCCI engine over a wide range of speeds and loads is probably the
most difficult hurdle facing HCCI engines. HCCI ignition is determined by the charge mixture
composition, its time-temperature history, and to a lesser extent pressure. Several potential control
methods have been proposed to control HCCI combustion: varying the amount of exhaust gasrecirculation (EGR), using a variable compression ratio (VCR), and using variable valve timing
(VVT) to change the effective compression ratio and/or the amount of hot exhaust gases retained in
the cylinder. VCR and VVT technologies are particularly attractive because their time response
could be made sufficiently fast to handle rapid transients (i.e., accelerations/decelerations). Although
these technologies have shown strong potential, performance is not yet fully proven, and cost and
reliability issues must be addressed.
Although HCCI engines have been demonstrated to operate well at low to medium loads, difficulties
have been encountered at high-load conditions. The combustion process can become very rapid and
intense causing unacceptable noise, potential engine damage, and eventually, unacceptable levels ofNOx emissions. Preliminary research indicates the operating range can be extended significantly by
partially stratifying the fuel/air/residual charge at high loads (mixture and/or temperature
stratification). Several potential mechanisms exist for achieving partial charge stratification,
including: in-cylinder fuel injection, water injection, varying the intake and in-cylinder mixing
processes, and altering in-cylinder flows to vary heat transfer. The extent to which these techniques
can extend the operating range, while preserving HCCI benefits, is currently unknown. Because of
the difficulty of high-load operation, most initial concepts involve switching to traditional SI or CIDI
combustion for operating conditions where HCCI operation is more difficult. This configuration
allows the benefits of HCCI to be realized over a significant portion of the driving cycle but adds thecomplexity of switching the engine between operating modes.
The fundamental processes of HCCI combustion make cold-starts difficult without some
compensating mechanism. Various mechanisms for cold-starting in HCCI mode have been proposed
such as using glow plugs, using a different fuel or fuel additive, and increasing the compression ratio
using VCR or VVT. Spark-ignition may be the most viable approach to cold-start, though it adds
cost and complexity.
HCCI engines have inherently low emissions of NOx and PM but relatively high emissions of
hydrocarbons (HC) and carbon monoxide (CO). Some potential exists to mitigate these emissions atlight load by using direct in-cylinder fuel injection. However, regardless of the ability to minimize
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engine-out HC and CO emissions, controlling HC and CO emissions from HCCI engines will likely
require use of an exhaust emission control device. Catalyst technology for HC and CO removal is
well understood and has been standard equipment on gasoline-fuelled automobiles for 25 years. In
addition, reducing HC and CO emissions from HCCI engines is much easier than reducing NOx and
PM emissions from CIDI engines. However, the cooler exhaust temperatures of HCCI engines mayincrease catalyst light-off time and decrease average effectiveness. Consequently, achieving stringent
future emission standards for HC and CO will likely require some further development of oxidation
catalysts for use with HCCI engines.
Fig.1 Side and Frontal views of the Nissan MK 2.5 Liter Engine.
2.HISTORYHCCI engines have a long history, even though HCCI has not been as widely implemented as spark
ignition or diesel injection. It is essentially an Otto combustion cycle. In fact, HCCI was popular
before electronic spark ignition was used. One example is the hot-bulb engine which used a hot
vaporization chamber to help mix fuel with air. The extra heat combined with compression induced
the conditions for combustion to occur. Homogeneous charge compression ignition (HCCI) engines
have the potential to provide high, diesel-like efficiencies and very low emissions. In an HCCI
engine, a dilute, premixed fuel/air charge auto ignites and burns volumetrically as a result of being
compressed by the piston. The charge is made dilute either by being very lean, or by mixing withrecycled exhaust gases.
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Several technical barriers must be overcome before HCCI can be implemented in production
engines. Variations of HCCI in which the charge mixture and/or temperature are partially stratified
(stratified charge compression ignition or SCCI) have the potential for overcoming many of these
barriers.
Because of HCCI's strong potential, most diesel engine and automobile manufacturers have
established HCCI/SCCI development efforts.
The Sandia HCCI Engine Combustion Fundamentals Laboratory supports this industrial effort. The
laboratory is equipped with two Cummins B-series engines mounted at either end of a double-ended
dynamometer. These production engines have been converted for single-cylinder HCCI/SCCI
operation.
One engine (the so-called all-metal engine) is used to establish operating points, test various fuel
types, develop combustion-control strategies, and investigate emissions.The second engine has extensive optical access for the application of advanced laser diagnostics for
investigations of in-cylinder processes. The design includes an extended piston with piston-crown
window, three large windows near the top of the cylinder wall, and a drop-down cylinder for rapid
cleaning of fouled windows.
The engines are designed to provide a versatile facility for investigations of a wide range of
operating conditions and various fuel-injection, fuel/air/residual mixing, and control strategies that
have the potential of overcoming the technical barriers to HCCI. The size of these engines (0.98
litres/cylinder) was selected so that results are applicable to both automotive and heavy-duty
applications. They are equipped with the following features:
Variable in-cylinder swirl: swirl ratios of 0.9 to 3.2, convertible to swirl ratios up to 7.6.
Multiple fuel systems: fully premixed, port fuel injection, gasoline-type direct-injection, and diesel-
type direct-injection.
Complete intake charge conditioning: simulated or real EGR, intake pressures to 6 atmospheres,
and intake temperatures to 220C. Speeds up to 3600 rpm (metal engine) and 1800 rpm (optical
engine) Variable compression ratio variable through interchangeable pistons (compression ratios
from 12:1 to 21:1 are currently available) Custom HCCI piston design.
Full emissions measurements: CO2, CO, O2, HC, NOx, and smoke
Mechanical valves with a conversion to fully flexible variable valve actuation (VVA) under
development.
Investigations are addressing several issues, including:
Stratification of the fuel/air mixture as a means of improving emissions and combustion efficiency
during part-load operation. The effects of fuel-type on performance and emissions over a range of
speeds and loads Intake pressure boosting for increased power, heat transfer effects, combustion-
phasing control, and extending operation to higher loads.
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Because fuel characteristics are central to HCCI engine design, a variety of fuels are being examined
including gasoline, diesel fuel, and a number of representative constituents of real distillate fuels.
3.WHAT IS HCCI?HCCI is an alternative piston-engine combustion process that can provide efficiencies as high as
compression-ignition, direct-injection (CIDI) engines (an advanced version of the commonly known
diesel engine) while, unlike CIDI engines, producing ultra-low oxides of nitrogen (NOx) and
particulate matter (PM) emissions. HCCI engines operate on the principle of having a dilute,
premixed charge that reacts and burns volumetrically throughout the cylinder as it is compressed by
the piston. In some regards, HCCI incorporates the best features of both spark ignition (SI) and
compression ignition (CI), as shown in Figure 1. As in an SI engine, the charge is well mixed, which
minimizes particulate emissions, and as in a CIDI engine, the charge is compression ignited and has
no throttling losses, which leads to high efficiency. However, unlike either of these conventional
engines, the combustion occurs simultaneously throughout the volume rather than in a flame front.
This important attribute of HCCI allows combustion to occur at much lower temperatures,
dramatically reducing engine-out emissions of NOx.
Most engines employing HCCI to date have dual mode combustion systems in which traditional SI
or CI combustion is used for operating conditions where HCCI operation is more difficult. Typically,
the engine is cold-started as an SI or CIDI engine, then switched to HCCI mode for idle and low- to
mid-load operation to obtain the benefits of HCCI in this regime, which comprises a large portion of
typical automotive driving cycles. For high-load operation, the engine would again be switched to SIor CIDI operation. Research efforts are underway to extend the range of HCCI operation.
Fig.2 Homogeneous Charge Compression Ignition
4.WHYHCCI?
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The modern conventional SI engine fitted with a three-way catalyst can be seen as an very clean
engine. But it suffers from poor part load efficiency. As mentioned earlier this is mainly due to the
throttling. Engines in passenger cars operate most of the time at light- and partload conditions. For
some shorter periods of time, at overtaking and acceleration, they run at high loads, but they seldom
run at high loads for any longer periods. This means that the overall efficiency at normal drivingconditions becomes very low.
The Diesel engine has much higher part load efficiency than the SI engine. Instead the Diesel engine
fights with great smoke and NOx problems. Soot is mainly formed in the fuel rich regions and NOx
in the hot stoichiometric regions. Due to these mechanisms, it is difficult to reduce both smoke and
NOx simultaneously through combustion improvement. Today, there is no well working exhaust
after treatment that takes away both soot and NOx.
The HCCI engine has much higher part load efficiency than the SI engine and comparable to the
Diesel engine, and has no problem with NOx and soot formation like the Diesel engine. In summary,the HCCI engine beats the SI engine regarding the efficiency and the Diesel engine regarding the
emissions.
5.FUNDAMENTALS & REQUIREMENTS OF HCCI
5.1 HCCI Fundamentals
The HCCI PrincipleHCCI means that the fuel and air should be mixed before combustion starts
and that the mixture is auto ignited due to the increase in temperature from the compression stroke.
Thus HCCI is similar to SI in the sense that both engines use a premixed charge and HCCI is similar
to CI as both rely on auto ignition for combustion initiation. However, the combustion process is
totally different for the three types. Figure 4 shows the difference between (a) SI combustion and (b)
HCCI. In the SI engine we have three zones, a burnt zone, an unburned zone and between them a
thin reaction zone where the chemistry takes place. This reaction zone propagates through the
combustion chamber and thus we have flame propagation. Even though the reactions are fast in thereaction zone, the combustion process will take some time as the zone must propagate from spark
plug (zero mass) to the far liner wall (mass wi ). With the HCCI process the entire mass in the
cylinder will react at once. The right part of Figure 4 shows HCCI, or as Onishi called it Active
Thermo-Atmosphere Combustion, ATAC. We see that the entire mass is active but the reaction rate
is low both locally and globally. This means that the combustion process will take some time even if
all the charge is active. The total amount of heat released, Q, will be the same for both processes.
It could be noted that the combustion process can have the same duration even though HCCI
normally has a faster burn rate. Initial tests in Lund on a two stroke engine revealed the fundamental
difference between these two types of engines
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Fig.3 shows the concept of HCCI engine.
Fig.4 The temperature history in K for is preventative ODT simulation. The vertical
Axis corresponds to a slice through the cylinder. Ignition occurs following
compression, heating and turbulent mixing.
Fig.5 this pressure trace shows the differences between completely homogeneous mixtures and
mixtures with small-scale inhomogeneities.
5.2 Requir ements For HCCI
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The HCCI combustion process puts two major requirements on the conditions in the cylinder: (a)
The temperature after compression stroke should equal the auto ignition temperature of the fuel/air
mixture. (b) The mixture should be diluted enough to give reasonable burn rate.
For iso-octane, the auto ignition temperature is roughly 1000K. This means that the temperature inthe cylinder should be 1000 K at the end of the compression stroke where the reactions should start.
This temperature can be reached in two ways, either the temperature in the cylinder at the start of
compression is controlled or the increase in temperature due to compression i.e. compression ratio is
controlled. It
could be interesting to note that the autoignition temperature is a very weak function of air/fuel ratio.
The change in autoignition temperature for iso-octane is only 50K with a factor 2 change in . Figure
7 also shows the normal rich and lean limits found with HCCI. With a too rich mixture the reactivity
of the charge is too high. This means that the burn rate becomes
extremely high with richer mixtures. If an HCCI engine is run too rich the entire charge can beconsumed within a fraction of a crank angle. This gives rise to extreme pressure rise rates and hence
mechanical stress and noise. With a high autoignition temperature like that of natural gas, it is also
possible that formation of NOx can be the load limiting factor. Figure 8 shows the NO formation as a
function of maximum temperature.
Very low emission levels are measured with ethanol. If the combustion starts at a higher temperature
like with natural gas, the temperature after combustion will also be higher for a given amount of heat
released. On the lean side, the temperature increase from the combustion is too low to have complete
combustion. Partial oxidation of fuel to CO can occur at extremely lean mixtures; above 14 has
been tested. However, the oxidation of CO to CO2 requires a temperature of 1400-1500 K. As asummary, HCCI is governed by three temperatures. We need to reach the autoignition temperature to
get things started; the combustion should then increase the temperature to at least 1400 K to have
good combustion efficiency but it should not be increased to more than 1800 K to prevent NO
formation.
6.OPERATION
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6.1Methods
A mixture of fuel and air will ignite when the concentration and temperature of reactants is
sufficiently high. The concentration and/or temperature can be increased by several different ways:Methods
1. High compression ratio
2. Pre-heating of induction gases
3. Forced induction
4. Retained or re-inducted exhaust gases
Once ignited, combustion occurs very quickly. When auto-ignition occurs too early or with too much
chemical energy, combustion is too fast and high in-cylinder pressures can destroy an engine. For
this reason, HCCI is typically operated at lean overall fuel mixtures.
6.2Advantages HCCI provides up to a 30-percent fuel savings, while meeting current emissions standards. Since HCCI engines are fuel-lean, they can operate at a Diesel-like compression ratios (>15),
thus achieving higher efficiencies than conventional spark-ignited gasoline engines.
Homogeneous mixing of fuel and air leads to cleaner combustion and lower emissions.Actually, because peak temperatures are significantly lower than in typical spark ignitedengines, NOxlevels are almost negligible. Additionally, the premixed lean mixture does not
produce soot.
HCCI engines can operate on gasoline, diesel fuel, and most alternative fuels. In regards to gasoline engines, the omission of throttle losses improves HCCI efficiency.6.3 Disadvantages
High in-cylinder peak pressures may cause damage to the engine. High heat release and pressure rise rates contribute to engine wear. The autoignition event is difficult to control, unlike the ignition event in spark ignition (SI)
and diesel engines which are controlled by spark plugs and in-cylinder fuel injectors,respectively.
HCCI engines have a small power range, constrained at low loads by lean flammability limitsand high loads by in-cylinder pressure restrictions.
Carbon monoxide (CO) and hydrocarbon (HC) pre-catalyst emissions are higher than atypical spark ignition engine, caused by incomplete oxidation (due to the rapid combustion
event and low in-cylinder temperatures) and trapped crevice gases, respectively.
6.4 Control
http://en.wikipedia.org/wiki/Nitrogen_oxidehttp://en.wikipedia.org/wiki/Nitrogen_oxidehttp://en.wikipedia.org/wiki/Nitrogen_oxidehttp://en.wikipedia.org/wiki/Soothttp://en.wikipedia.org/wiki/Spark_ignitionhttp://en.wikipedia.org/wiki/Diesel_enginehttp://en.wikipedia.org/wiki/Carbon_monoxidehttp://en.wikipedia.org/wiki/Hydrocarbonhttp://en.wikipedia.org/wiki/Hydrocarbonhttp://en.wikipedia.org/wiki/Carbon_monoxidehttp://en.wikipedia.org/wiki/Diesel_enginehttp://en.wikipedia.org/wiki/Spark_ignitionhttp://en.wikipedia.org/wiki/Soothttp://en.wikipedia.org/wiki/Nitrogen_oxide -
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Controlling HCCI is a major hurdle to more widespread commercialization. HCCI is more difficult
to control than other popular modern combustion engines, such as Spark Ignition (SI) and Diesel. In
a typical gasoline engine, a spark is used to ignite the pre-mixed fuel and air. In Diesel engines,
combustion begins when the fuel is injected into compressed air. In both cases, the timing of
combustion is explicitly controlled. In an HCCI engine, however, the homogeneous mixture of fuel
and air is compressed and combustion begins whenever the appropriate conditions are reached. Thismeans that there is no well-defined combustion initiator that can be directly controlled. Engines can
be designed so that the ignition conditions occur at a desirable timing. To achieve dynamic operation
in an HCCI engine, the control system must change the conditions that induce combustion. Thus, the
engine must control either the compression ratio, inducted gas temperature, inducted gas pressure,
fuel-air ratio, or quantity of retained or re-inducted exhaust. Several control approaches are discussed
below.
6.4.1 The Need For Control
For better understanding of the combustion process, laser diagnostics is needed and this knowledge
can be used to optimize the system. However, the HCCI process is very sensitive to disturbances. It
can be sufficient to change the inlet temperature 2C to move from a very good operating point to a
total misfire. This sensitivity makes the HCCI engine require closed loop combustion control, CLCC.
Closed loop control requires as always a sensor, control algorithm and control means. The main
parameter to control for HCCI is the combustion timing i.e. when in the cycle combustion
takes place. Figure 17 shows the rate of heat release for a range of timings. With early phasing the
rate of heat release is higher and as it is phased later the burn rate goes down. With combustion
before top dead centre, TDC, the temperature will be increased both by the chemical reactions and
the compression due to piston motion. Thus for a given auto ignition temperature, combustion onset
before TDC will result in faster reactions. With the conditions changed to give combustion onset
close to TDC, the temperature will not be increased by piston motion, the only temperature
driver would be the chemical reactions. This gives a more sensitive system and the later the
combustion phasing the more sensitive the system is. This is the underlying problem with HCCI
combustion control. We want a late combustion phasing to reduce burn rate and hence pressure rise
rate and peak pressure but on the other hand we cannot accept too much variations in
the combustion process. How late we can go depends on the quality of the control system. With a
fast and accurate control system we can go later and hence reduce the noise and mechanical loads of
the engine.
6.4.2 Var iable compression ratio
There are several methods for modulating both the geometric and effective compression ratio. The
geometric compression ratio can be changed with a movable plunger at the top of the cylinder head.
This is the system used in "diesel" model aircraft engines. The effective compression ratio can be
reduced from the geometric ratio by closing the intake valve either very late or very early with some
form of variable valve actuation (i.e. variable valve timingpermitting Miller cycle). Both of the
approaches mentioned above require some amounts of energy to achieve fast responses.
Additionally, implementation is expensive. Control of an HCCI engine using variable compression
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ratio strategies has been shown effective.[8]The effect of compression ratio on HCCI combustion has
also been studied extensively.[9]
6.4.3Variable induction temperature
In HCCI engines, the autoignition event is highly sensitive to temperature. Various methods have
been developed which use temperature to control combustion timing. The simplest method uses
resistance heaters to vary the inlet temperature, but this approach is slow (cannot change on a cycle-
to-cycle basis).[10]Another technique is known as fast thermal management (FTM). It is
accomplished by rapidly varying the cycle to cycle intake charge temperature by rapidly mixing hot
and cold air streams.[11]It is also expensive to implement and has limited bandwidth associated with
actuator energy.
6.4.4 Variable exhaust gas percentage
Exhaust gas can be very hot if retained or re-inducted from the previous combustion cycle or cool if
recirculated through the intake as in conventional EGRsystems. The exhaust has dual effects on
HCCI combustion. It dilutes the fresh charge, delaying ignition and reducing the chemical energy
and engine work. Hot combustion products conversely will increase the temperature of the gases in
the cylinder and advance ignition. Control of combustion timing HCCI engines using EGR has been
shown experimentally.[12]
6.4.5 Var iable valve actuati on
Variable valve actuation (VVA) has been proven to extend the HCCI operating region by giving
finer control over the temperature-pressure-time history within the combustion chamber. VVA can
achieve this via two distinct methods:
Controlling the effective compression ratio: A variable duration VVA system on intake cancontrol the point at which the intake valve closes. If this is retarded past bottom dead center
(BDC), then the compression ratio will change, altering the in-cylinder pressure-time history
prior to combustion. Controlling the amount of hot exhaust gas retained in the combustion chamber: A VVA
system can be used to control the amount of hot internal exhaust gas recirculation (EGR)
within the combustion chamber. This can be achieved with several methods, including valve
re-opening and changes in valve overlap. By balancing the percentage of cooled external
EGR with the hot internal EGR generated by a VVA system, it may be possible to control the
in-cylinder temperature.
While electro-hydraulic and camless VVA systems can be used to give a great deal of control over
the valve event, the componentry for such systems is currently complicated and expensive.
Mechanical variable lift and duration systems, however, although still being more complex than a
standard valvetrain, are far cheaper and less complicated. If the desired VVA characteristic is known,
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then it is relatively simple to configure such systems to achieve the necessary control over the valve
lift curve. Also see variable valve timing.
6.4.6 Variable fuel igniti on quality
Another means to extend the operating range is to control the onset of ignition and the heat release
rate[13][14]by manipulating the fuel itself. This is usually carried out by adopting multiple fuels and
blending them "on the fly" for the same engine.[15]Examples could be blending of commercial
gasoline and diesel fuels,[16]adopting natural gas[17]or ethanol ".[18]This can be achieved in a
number of ways;
Blending fuels upstream of the engine: Two fuels are mixed in the liquid phase, one with lowresistance to ignition (such as diesel fuel) and a second with a greater resistance (gasoline),
the timing of ignition is controlled by varying the compositional ratio of these fuels. Fuel is
then delivered using either a port or direct injection event. Having two fuel circuits: Fuel A can be injected in the intake duct (port injection) and Fuel B
using a direct injection (in-cylinder) event, the proportion of these fuels can be used to
control ignition, heat release rate as well as exhaust gas emissions.
6.4.7 Direct In jection: PCCI or PPCI Combustion
Compression Ignition Direct Injection (CIDI) combustion is a well-established means of controlling
ignition timing and heat release rate and is adopted in diesel engine combustion. Partially Pre-mixed
Charge Compression Ignition (PPCI) also known as Premixed Charge Compression Ignition (PCCI)
is a compromise between achieving the control of CIDI combustion but with the exhaust gas
emissions of HCCI, specifically soot.[19]On a fundamental level, this means that the heat release rate
is controlled preparing the combustible mixture in such a way that combustion occurs over a longer
time duration and is less prone to knocking. This is done by timing the injection event such that the
combustible mixture has a wider range of air/fuel ratios at the point of ignition, thus ignition occurs
in different regions of the combustion chamber at different times - slowing the heat release rate.
Furthermore this mixture is prepared such that when combustion occurs there are fewer rich pockets
thus reducing the tendency for soot formation.[20]The adoption of high EGR and adoption of diesel
fuels with a greater resistance to ignition (more "gasoline like") enables longer mixing times prior to
ignition and thus fewer rich pockets thus resulting in the possibility of both lower soot emissions andNox.
6.5 H igh Peak Pressur es and Heat Release Rates
In a typical gasoline or diesel engine, combustion occurs via a flame. Hence at any point in time,
only a fraction of the total fuel is burning. This results in low peak pressures and low energy release
rates. In HCCI, however, the entire fuel/air mixture ignites and burns nearly simultaneously resulting
in high peak pressures and high energy release rates. To withstand the higher pressures, the engine
has to be structurally stronger and therefore heavier. Several strategies have been proposed to lowerthe rate of combustion. Two different fuels, with different autoignition properties, can be used to
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lower the combustion speed.[21]However, this requires significant infrastructure to implement.
Another approach uses dilution (i.e. with exhaust gases) to reduce the pressure and combustion rates
at the cost of work production.[22]
6.6 Power
In both a spark ignition engine and diesel engine, power can be increased by introducing more fuel
into the combustion chamber. These engines can withstand a boost in power because the heat release
rate in these engines is slow. However, in HCCI engines the entire mixture burns nearly
simultaneously. Increasing the fuel/air ratio will result in even higher peak pressures and heat release
rates. In addition, many of the viable control strategies for HCCI require thermal preheating of the
charge which reduces the density and hence the mass of the air/fuel charge in the combustion
chamber, reducing power. These factors make increasing the power in HCCI engines challenging.
One way to increase power is to use fuels with different autoignitionproperties. This will lower theheat release rate and peak pressures and will make it possible to increase the equivalence ratio.
Another way is to thermally stratify the charge so that different points in the compressed charge will
have different temperatures and will burn at different times lowering the heat release rate making it
possible to increase power.[23]A third way is to run the engine in HCCI mode only at part load
conditions and run it as a diesel or spark ignition engine at full or near full load conditions .[24]Sincemuch more research is required to successfully implement thermal stratification in the compressed
charge, the last approach is being studied more intensively.
6.7 Emissions
Because HCCI operates on lean mixtures, the peak temperatures are lower in comparison to spark
ignition (SI) and Diesel engines. The low peak temperatures prevent the formation of NOx. This
leads to NOx emissions at levels far less than those found in traditional engines. However, the low
peak temperatures also lead to incomplete burning of fuel, especially near the walls of the
combustion chamber. This leads to high carbon monoxide and hydrocarbon emissions. An oxidizing
catalyst would be effective at removing the regulated species because the exhaust is still oxygen rich.
Fig.6 shows the emission characteristics.
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6.9Simulation of HCCI Engines
The development of computational models for simulating combustion and heat release rates of HCCI
engines has required the advancement of detailed chemistry models.[16][25][26]This is largely becauseignition is most sensitive to chemical kinetics rather than turbulence/spray or spark processes as are
typical in direct injection compression ignition or spark ignition engines. Computational models have
demonstrated the importance of accounting for the fact that the in-cylinder mixture is actually in-
homogeneous, particularly in terms of temperature. This in-homogeneity is driven by turbulent
mixing and heat transfer from the combustion chamber walls, the amount of temperature
stratification dictates the rate of heat release and thus tendency to knock.[27]This limits the
applicability of considering the in-cylinder mixture as a single zone resulting in the uptake of 3D
computational fluid dynamics codes such as Los Alamos National Laboratory's KIVA CFD code and
faster solving probability density function modelling codes.
7. 6.8Di ff erence fr om Knock8. Engine knock or pinging occurs when some of the unburnt gases ahead of the flame in a
spark ignited engine spontaneously ignite. The unburnt gas ahead of the flame is compressed
as the flame propagates and the pressure in the combustion chamber rises. The high pressure
and corresponding high temperature of unburnt reactants can cause them to spontaneously
ignite. This causes a shock wave to traverse from the end gas region and an expansion wave
to traverse into the end gas region. The two waves reflect off the boundaries of the
combustion chamber and interact to produce high amplitude standing waves.
9. A similar ignition process occurs in HCCI. However, rather than part of the reactant mixturebeing ignited by compression ahead of a flame front, ignition in HCCI engines occurs due topiston compression. In HCCI, the entire reactant mixture ignites (nearly) simultaneously.
Since there are very little or no pressure differences between the different regions of the gas,
there is no shock wave propagation and hence no knocking. However, at high loads (i.e. high
fuel/air ratios), knocking is a possibility even in HCCI.
7PROTOTYPESAs of 2012, there were no HCCI engines being produced in commercial scale. However, several car
manufacturers have fully functioning HCCI prototypes.
In 2007-2009, General Motors has demonstrated HCCI with a modified 2.2 L Family IIengine installed in Opel Vectra and Saturn Aura,.[30][31][32]The engine operates in HCCI
mode at speeds below 60 miles per hour (97 km/h) or when cruising, switching to
conventional spark-ignition when the throttle is opened, and produces fuel economy of
43 miles per imperial gallon (6.6 L/100 km; 36 mpg-US) and carbon dioxide emissions of
about 150 grams per kilometer, improving on 37 miles per imperial gallon (7.6 L/100 km;
31 mpg-US) and 180 g/km of the conventional 2.2 L direct injection version.[33]GM is also
researching smallerFamily 0 engines for HCCI applications. GM has used KIVA in the
development of direct-injection, stratified charge gasoline engines as well as the fast burn,homogeneous-charge gasoline engine.[29]
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Mercedes-Benz has developed a prototype engine called DiesOtto, with controlled autoignition. It was displayed in its F 700 concept car at the 2007 Frankfurt Auto Show.[34]
Volkswagen are developing two types of engine for HCCI operation. The first, calledCombined Combustion System orCCS, is based on the VW Group 2.0-litre diesel engine but
uses homogeneous intake charge rather than traditional diesel injection. It requires the use of
synthetic fuel to achieve maximum benefit. The second is called Gasoline CompressionIgnition orGCI; it uses HCCI when cruising and spark ignition when accelerating. Both
engines have been demonstrated in Touranprototypes, and the company expects them to be
ready for production in about 2015.[35][36]
In October 2005, the Wall Street Journal reported that Honda was developing an HCCIengine as part of an effort to produce a next generation hybrid car.[37]
Oxy-Gen Combustion, a UK-based Clean Technology company, has produced a full-loadHCCI concept engine with the aid of Michelin and Shell [2]
8OTHER APPLICATIONS OF HCCI RESEARCH
To date, there have been few prototype engines running in HCCI mode; however, the research efforts
invested into HCCI research have resulted in direct advancements in fuel and engine development.
Examples include:
PCCI/PPCI combustion - A hybrid of HCCI and conventional diesel combustion offeringmore control over ignition and heat release rates with lower soot and NOx emissions.
Advancements in fuel modelling - HCCI combustion is driven mainly by chemical kineticsrather than turbulent mixing or injection, reducing the complexity of simulating the chemistry
which results in fuel oxidation and emissions formation. This has led to increasing interest
and development of chemical kinetics which describe hydrocarbon oxidation.
Fuel blending applications - Due to the advancements in fuel modelling, it is now possible tocarry out detailed simulations of hydrocarbon fuel oxidation, enabling simulations of
practical fuels such as gasoline/diesel and ethanol. Engineers can now blend fuels virtually
and determine how they will perform in an engine context.
9 CHALLENGES FOR HCCICombustion is achieved by controlling the temperature, pressure and composition of the air/fuel
mixture so that it auto ignites near top dead centre (TDC) as it is compressed by the piston. This
mode of ignition is fundamentally more challenging than using a direct control mechanism such as a
spark plug or fuel injector to dictate ignition timing as in SI and CIDI engines, respectively. While
HCCI has been known for some twenty years, it is only with the recent advent of electronic engine
controls that HCCI combustion can be considered for application to commercial engines. Even so,
several technical barriers must be overcome before HCCI engines will be viable for high-volume
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production and application to a wide range of vehicles. The following describes the more significant
challenges for developing practical HCCI engines for transportation. Greater detail regarding these
technical barriers, potential solutions, and the R&D needed to overcome them are provided in this
section. Some of these issues could be mitigated or eliminated if the HCCI engine was used in a
series hybrid-electric application, as discussed above.
Fig.7 shows a relation between Temperature vs Crank Angle & Pressure vs Crank Angle
during combustion process of HCCI engine.
9.1 Controll ing I gnition Timingover a Range of Speeds and Loads Expanding the controlled
operation of an HCCI engine over a wide range of speeds and loads is probably the most difficult
hurdle facing HCCI engines. HCCI ignition is determined by the charge mixture composition and its
temperature history (and to a lesser extent, its pressure history). Changing the power output of an
HCCI engine requires a change in the fuelling rate and, hence, the charge mixture. As a result, the
temperature history must be adjusted to maintain proper combustion timing. Similarly, changing the
engine speed changes the amount of time for the auto ignition chemistry to occur relative to the
piston motion. Again, the temperature history of the mixture must be adjusted to compensate. These
control issues become particularly challenging during rapid transients. Several potential control
methods have been proposed to provide the compensation required for changes in speed and load.
Some of the most promising include varying the amount of hot EGR introduced into the incoming
charge, using a VCR mechanism to alter TDC temperatures, and using VVT to change the effective
compression ratio and/or the amount of hot residual retained in the cylinder. VCR and VVT areparticularly attractive because their time response could be made sufficiently fast to handle rapid
transients. Although these techniques have shown strong potential, they are not yet fully proven, and
cost and reliability issues must be addressed.
9.2 Extending the Operating Rangeto High Loads Although HCCI engines have been demonstrated
to operate well at low-to-medium loads, difficulties have been encountered at high-loads.
Combustion can become very rapid and intense, causing unacceptable noise, potential engine
damage, and eventually unacceptable levels of NOx emissions. Preliminary research indicates theoperating range can be extended significantly by partially stratifying the charge (temperature and
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mixture stratification) at high loads to stretch out the heat- release event. Several potential
mechanisms exist for achieving partial charge stratification, including varying in-cylinder fuel
injection, injecting water, varying the intake and in-cylinder mixing processes to obtain non-uniform
fuel/air/residual mixtures, and altering cylinder flows to vary heat transfer. The extent to which these
techniques can extend the operating range is currently unknown and R&D will be required. Becauseof the difficulty of high-load operation, most initial concepts involve switching to traditional SI or CI
combustion for operating conditions where HCCI operation is more difficult. This dual mode
operation provides the benefits of HCCI over a significant portion of the driving cycle but adds to the
complexity by switching the engine between operating modes.
9.3 Cold-Start Capabil ityAt cold start, the compressed-gas temperature in an HCCI engine will be
reduced because the charge receives no preheating from the intake manifold and the compressed
charge is rapidly cooled by heat transferred to the cold combustion chamber walls. Without some
compensating mechanism, the low compressed-charge temperatures could prevent an HCCI engine
from firing. Various mechanisms for cold-starting in HCCI mode have been proposed, such as using
glow plugs, using a different fuel or fuel additive, and increasing the compression ratio using VCR or
VVT. Perhaps the most practical approach would be to start the engine in spark-ignition mode and
transition to HCCI mode after warm-up. For engines equipped with VVT, it may be possible to make
this warm- up period as short as a few fired cycles, since high levels of hot residual gases could be
retained from previous spark-ignited cycles to induce HCCI combustion. Although solutions appear
feasible, significant R&D will be required to advance these concepts and prepare them for
production engines. 4. Hydrocarbon and Carbon Monoxide Emissions HCCI engines have inherently
low emissions of NOx and PM, but relatively high emissions of hydrocarbons (HC) and carbonmonoxide (CO). Some potential exists to mitigate these emissions at light load by using direct in-
cylinder fuel injection to achieve appropriate partial-charge stratification. However, in most cases,
controlling HC and CO emissions from HCCI engines will require exhaust emission control devices.
Catalyst technology for HC and CO removal is well understood and has been standard equipment on
automobiles for many years. However, the cooler exhaust temperatures of HCCI engines may
increase catalyst light-off time and decrease average effectiveness. As a result, meeting future
emission standards for HC and CO will likely require further development of oxidation catalysts for
low-temperature exhaust streams. However, HC and CO emission control devices are simpler, more
durable, and less dependent on scarce, expensive precious metals than are NOx and PM emissioncontrol devices. Thus, simultaneous chemical oxidation of HC and CO (in an HCCI engine) is much
easier than simultaneous chemical reduction of NOx and oxidation of PM (in a CIDI engine). In
addition, HC and CO emission control devices are simpler, more durable, and less dependent on
scarce, expensive precious metals.
9.4Var iable CompressionIgnition There are several methods of modulating both the geometric and
effective compression ratio. The geometric compression ratio can be changed with a movable
plunger at the top of the cylinder head. The effective compression ratio can be reduced from thegeometric ratio by closing the intake valve either very late or very early with some form of variable
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valve actuation (i.e. variable valve timing permitting Miller cycle). Both of the approaches
mentioned above require some amounts of energy to achieve fast responses and are expensive (no
more true for the 2nd solution, the variable valve timing being now maitrized). A 3rd proposed
solution is being developed by the MCE-5 society (new rod).
Mil ler cycle:
In engineering, the Miller cycle is a combustion process used in a type of four-stroke internal
combustion engine. The Miller cycle was patented by Ralph Miller, an American engineer, in the
1940s. This type of engine was first used in ships and stationary power-generating plant, but has
recently (late 1990s) been adapted by Mazda for use in their Millenia large sedan. The traditional
Otto cycle used four "strokes", of which two can be considered "high power" the compression and
power strokes. Much of the power lost in an engine is due to the energy needed to compress the
charge during the compression stroke, so systems to reduce this can lead to greater efficiency.
In the Miller cycle the intake valve is left open longer than it normally would be. This is the "fifth"
cycle that the Miller cycle introduces. As the piston moves back up in what is normally the
compression stroke, the charge is being pushed back out the normally closed valve. Typically this
would lead to losing some of the needed charge, but in the Miller cycle the piston in fact is over-fed
with charge from a supercharger, so blowing a bit back out is entirely planned. The supercharger
typically will need to be of the positive displacement kind (due its ability to produce boost at
relatively low RPM) otherwise low-rpm torque will suffer. The key is that the valve only closes, and
compression stroke actually starts, only when the piston has pushed out this "extra" charge, say 20 to
30% of the overall motion of the piston. In other words the compression stroke is only 70 to 80% aslong as the physical motion of the piston. The piston gets all the compression for 70% of the work.
The Miller cycle "works" as long as the supercharger can compress the charge for less energy than
the piston. In general this is not the case, at higher amounts of compression the piston is much better
at it. The key, however, is that at low amounts of compression the supercharger is more efficient than
the piston. Thus the Miller cycle uses the supercharger for the portion of the compression where it is
best, and the piston for the portion where it is best. All in all this leads to a reduction in the power
needed to run the engine by 10 to 15%. To this end successful production versions of this cycle have
typically used variable valve timing to "switch on & off" the Miller cycle when efficiency does not
meet expectation. In a typical Spark Ignition Engine however the Miller cycle yields another benefit.
Compression of air by the supercharger and cooled by an intercooler will yield a lower intake charge
temperature than that obtained by a higher compression. This allows ignition timing to be altered to
beyond what is normally allowed before the onset of detonation, thus increasing the overall
efficiency still further. A similar delayed valve closing is used in some modern versions of Atkinson
cycle engines, but without the supercharging.
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10. RECENT DEVELOPMENTS IN HCCIThere has been an exhaustive literature search of worldwide R&D on HCCI. Table 1 shows a
summary of recent developments in HCCI technology. In addition, Ford, General Motors (GM), and
Cummins Engine Company have been performing research on HCCI combustion. Ford motor
company has an active research program in HCCI combustion. Researchers are using optical
diagnostics in single-cylinder engines to explore viable HCCI operating regimes and to investigate
methods of combustion control. In addition, chemical kinetic and cycle simulation models are being
applied to better understand the fundamentals of the HCCI process and to explore methods of
implementing HCCI technology. GM at a research level is evaluating the potential for incorporating
HCCI combustion into engine systems. This work includes assessing the strengths and weaknesses of
HCCI operation relative to other advanced concepts, assessing how best to integrate HCCI
combustion into a viable powertrain, and the development of appropriate modelling tools. Work is
focused on fuels, combustion control, combustion modelling, and mode transitioning between HCCI
and traditional SI or CI combustion. GM is also supporting HCCI work at the university level.
Cummins has been researching HCCI for almost 15 years. Industrial engines run in-house using
HCCI combustion of natural gas have achieved remarkable emission and efficiency results.
However, Cummins has found that it is quite challenging to control the combustion phasing over a
real-world operating envelope including variations in ambient conditions, fuel quality variation,
speed and load. Because the new diesel emissions targets are beyond the capability of conventional
diesel engines, Cummins is investigating all options, including HCCI, as part of their design palette
and future engine strategy.
11. CONCLUSION
A high-efficiency, gasoline-fuelled HCCI engine represents a major step beyond SIDI engines for
light-duty vehicles. HCCI engines have the potential to match or exceed the efficiency of diesel-
fuelled CIDI engines without the major challenge of NOx and PM emission control or a major
impact on fuel-refining capability. Also, HCCI engines would probably cost less than CIDI engines
because HCCI engines would likely use lower-pressure fuel-injection equipment, and the combustion
characteristics of HCCI would potentially enable the use of emission control devices that depend less
on scarce and expensive precious metals. In addition, for heavy-duty vehicles, successful
development of the diesel- fuelled HCCI engine is an important alternative strategy in the event that
CIDI engines cannot achieve future NOx and PM emissions standards.
12. REFERENCES
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1. Najt, P. M. and Foster, D. E., "Compression- Ignited Homogeneous Charge Combustion," SAE
paper 830264, 1983.
2. Noguchi, M., Tanaka, Y., Tanaka, T., and Takeuchi, Y., "A Study on Gasoline Engine
Combustion by Observation of Intermediate Reactive Products During Combustion," SAE paper
790840, 1979.
3. Iida, N., "Alternative Fuels and Homogeneous Charge Compression Ignition Combustion
Technology," SAE paper 972071, 1997.
4. Aceves, S. M., Flowers, D. L., Westbrook, C. K., Smith, J. R., Pitz, W., Dibble, R., Christensen,
M., and Johansson, B., "A Multi-Zone Model for Prediction of HCCI Combustion and Emissions,"
SAE paper no. 2000- 01-0327, 2000.
5. Kelly-Zion, P. L., and Dec, J. E. "A Computational Study of the Effect of Fuel Type on Ignition
Time in HCCI Engines," accepted for presentation at and publication in the proceedings of the 2000
International Combustion Symposium.
6. Christensen M., Hultqvist, A. and Johansson, B., "Demonstrating the Multi-Fuel Capability of a
Homogeneous Charge Compression Ignition Engine with Variable Compression Ratio," SAE Paper,
No. 1999-01-3679, 1999.
7. Flynn P. et al., "Premixed Charge Compression Ignition Engine with Optimal CombustionControl," International Patent WO9942718, World Intellectual Property Organization.