Roger Krieger, GM R&D Center

Diesel Fuel

If you have ever compared diesel fuel and gasoline, you know that they are different .They certainly smell different .Diesel fuel is heavier and oilier .

Diesel fuel evaporates much more slowly than gasoline -- its boiling point is actually

higher than the boiling point of water .You will often hear diesel fuel referred to as

"diesel oil" because it is so oily .

Diesel fuel evaporates more slowly because it is heavier .

It contains more carbon atoms in longer chains than gasoline does (gasoline is typically C9H20, while diesel fuel is typically C14H30) .

It takes less refining to create diesel fuel, which is why it is generally cheaper than gasoline .

DIESEL FUEL

Diesel fuel must meet an entirely different set of standards than gasoline .The fuel in a diesel engine is not ignited with a spark, but is ignited by the heat

generated by high compression .All diesel fuel must be clean, be able to flow at low temperatures, and be of the proper cetane rating.Cleanliness .Low-temperature fluidity .

Cetane number.

Diesel Fuel CharacteristicsCetane numberMeasure of relative ease to initiate combustionHigher number: easier to ignite

Octane number for gas: oppositeHigher number: less tendency to ignite

Cetane NumberIgnition quality measureAffects: cold starting, warm-up, combustion roughness, acceleration, and exhaust smoke densityCetane number is based on the ignition characteristics of two hydrocarbons:

Cetane - short delay period and ignites readily (100)Alphamethylnaphthalene (AMN) - long delay period and poor ignition quality (0)It is the percentage by volume of normal cetane in a blend with AMN

PC engines require a minimum cetane no. of 35DI engines require a minimum cetane no. of 40

Cetane NumberHigh cetane number indicates good ignition quality (short delay period)Low cetane number indicates poor ignition quality (long delay period)

PC engines require a minimum cetane # of 35

DI engines require a minimum cetane # of 40Cetane improver additive can improve ignition quality and reduce white smoke during start up

FUEL CYCLE

Fuel Injection In CI Engines

Delay Period

Rapid Combustion - knock

Diffusion Combustion - smoke

Cylinder Pressure

Fuel Injection In CI Engines

Less air means less fuel required

Fuel injection system has to compensate for air

density to minimize smoke output

7% decrease in air density per 1000m altitude

FUEL FILTERS

The fuel filtration and water separation needs of today's new generation

diesel fuel systems demand extremely high efficiency, flexibility, multiple

functions and ease of use with no risk of fuel spills or contaminated parts.

Stan dyne's patented Fuel Manager® range of Available for light, medium and heavy duty trucks; and agricultural,industrial, construction and marine

applications, there is a Fuel Manager

The FM10 Series is designed for diesel engines with a fuel flow rate up

to 50 US gallons/hr (190 liters/hr). Typical engines range from 10 to 200 HP The FM100 Series is designed for

diesel engines with a fuel flow rate upto 80 US gallons/hr (300 liters/hr). Typical engines range from 50 to 350 HP.

The FM1000 Series is designed for diesel engines with a fuel flow rateup to 180 US gallons/hr (680 liters/hr). Typical engines range from 200 to

Types of filters

Fuel pump

The ‘traditional’ style of injection pump is the in-line pump. They have been used for many

decades and are still commonly found on agricultural and stationary diesels, and very many older

model diesel road vehicles still employ them, including the Toyota Landcruiser 2H diesel.. They

are typically capable of generating injection nozzle pressures up to about 750 bar in light road

vehicles – towards the lower end of the range that is required these days.

They have a separate pump plunger for each cylinder of the engine, so a 4 cylinder engine has a four plunger pump, a 6 cylinder engine has a six plunger pump, etc. The pump is run at half engine crankshaft speed and has a central shaft with four/six etc. cam lobes attached. So, each plunger is operated by it’s cam once every two crankshaft revolutions, coinciding of course with the power stroke of its engine cylinder. Each plunger has a spiral groove or helix machined on it’s side and cut through to the top of the plunger. When operated, the plunger is pushed up by its cam lobe. At a certain point the spiral groove will line up with a spill port on the side of the plunger cylinder and the rest of the fuel is ‘spilled’.

Because the groove is a spiral shape, the point in the plunger stroke when it uncovers the spill port

will vary as the plunger is rotated a few degrees either way. This adjusts the spill point and hence,

the volume of its fuel charge to the engine cylinder.

So that all engine cylinders receive the same sized fuel charge, all of the plungers are rotated

together. This is achieved by each plunger having gear teeth machined to it’s circumference which

are engaged by a common gear rack which runs through the pump body. As the rack moves back

and forth, all four (or six or more) plungers are rotated together. The extremes of travel of the

pump rack control the minimum and maximum fuel charge quantities the pump is capable of

PRE SUPPLY PUMP

The electric fuel pump comprises of:1.Electric Motor

2.Roller-Cell Pump3.Non Return Valve

The roller cell is driven by an electric motor.

Its rotor is mounted eccentrically and provided with slots in which movable rollers are free to travel.

PRE SUPPLY PUMP

The rollers are forced against the base plate by rotation and by fuel pressure.

The fuel is transported to the outlet openings on the pump’s pressure side.

PRE SUPPLY PUMP

Gear type fuel pump The drive gear

wheel is driven by the engine.

Delivery quantity is directly proportional

to engine speed. Shut off is by means

of an electromagnet..

PRE SUPPLY PUMPvariants

High- pressure pump

The pump plunger moves downwards The inlet valve opens

The fuel is drawn in to the pumping element chamber(suction stroke)

At BDC, the inlet valve closes The fuel in the chamber can be compressed

by the upward moving plunger.

High- pressure pump

High- pressure accumulator (Rail)

Store fuelPrevent pressure fluctuations

Rail is a forged-steel tube.ID is approx.. 10mmLength is between 280 and 600mm

The volume must be “ as small as possible, as large as necessary”

High- pressure accumulator (Rail)

Pressure-control valve (DRV)

Responsible for maintaining the pressure in the rail at a constant level.

The injector on a diesel engine is its most complex component and has been the subject of a great deal of experimentation -- in any particular engine it may be located in a variety of places .

The injector has to be able to withstand the temperature and pressure inside the cylinder and still deliver the fuel in a fine mist .

Fuel Injector

Getting the mist circulated in the cylinder so that it is evenly distributed is also a problem, so some diesel engines employ special induction valves, pre-combustion chambers or other devices to swirl the air in the combustion chamber or otherwise improve the ignition and combustion process .

CI Engine Combustion Chambers

Two types:Indirect (divided

chamber) injection - into a pre-

combustion chamber

CI Engine Combustion Chambers

Two types:Direct injection -

into cylinder

Combustion Chamber Comparison

IndirectGood

Excellent mixing, turbulence characteristics

Can burn lower quality fuelLower injection pressureLess pronounced knock

Combustion Chamber Comparison

IndirectBad

Very high temperature/pressure in injection chamber

Higher emissions, especially NOx

Harder to start - glow plugsLess efficient

Combustion Chamber Comparison

DirectBad

Pressure rise can be great, knock

High injection pressure, high quality fuel

Combustion Chamber Comparison

DirectGood

Lower specific fuel consumption - 20%

Lower emissionsBigger valves, higher

volumetric efficiency

Direct Injection

Air-fuel mixing importantControlled by:

Use of swirl-inducing designsIntake port geometryPiston cap geometry

Injection system designHigh pressureMany nozzle holesPositioning

Bad: high-tech injection system

Good: Higher volumetric efficiency

DIESEL ENGINESIndirect and Direct Injection

FIGURE 4-4 A direct injection diesel engine injects the fuel directly into the combustion

chamber. Many designs do not use a glow plug.

DIESEL ENGINESIndirect and Direct Injection

In an indirect injection

(abbreviated IDI) diesel engine, fuel is injected into a small

prechamber, which is connected to the

cylinder by a narrow opening .

The initial combustion takes place in this

prechamber .This has the effect of

slowing the rate of combustion, which

tends to reduce noise. FIGURE 4-3 An indirect injection diesel engine uses a prechamber and a glow

plug.

DIESEL ENGINESDiesel Fuel Ignition

Ignition occurs in a diesel engine by injecting fuel into the air charge,

which has been heated by compression to a temperature

greater than the ignition point of the fuel or about 1,000°F (538°C).

Roger Krieger, GM R&D Center

Fuel Injection Systems

Electronic distributor pump

Electronic unit injector (EUI)

High-pressure common rail

Electronic Distributor Pump

Roger Krieger, GM R&D Center

Electronic Unit Injector (EUI)

High-Pressure Common Rail

High-Pressure PumpECU

Fuel Return to

Tank

Common Rail

Injectors

Spill Control Valve