Energy Conversion and Management 51 (2010) 2239–2244

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Energy Conversion and Management

journal homepage: www.elsevier .com/ locate /enconman

Design of a new SI engine intake manifold with variable length plenum

M.A. Ceviz *, M. AkınDepartment of Mechanical Engineering, Faculty of Engineering, University of Atatürk, Erzurum 25240, Turkey

a r t i c l e i n f o

Article history:Received 5 August 2009Accepted 21 March 2010

Keywords:Intake manifoldIntake plenumEngine performance

0196-8904/$ - see front matter � 2010 Elsevier Ltd. Adoi:10.1016/j.enconman.2010.03.018

* Corresponding author. Fax: +90 442 236 09 57.E-mail address: aceviz@atauni.edu.tr (M.A. Ceviz).

a b s t r a c t

This paper investigates the effects of intake plenum length/volume on the performance characteristics ofa spark-ignited engine with electronically controlled fuel injectors. Previous work was carried out mainlyon the engine with carburetor producing a mixture desirable for combustion and dispatching the mixtureto the intake manifold. The more stringent emission legislations have driven engine developmenttowards concepts based on electronic-controlled fuel injection rather than the use of carburetors. Inthe engine with multipoint fuel injection system using electronically controlled fuel injectors has anintake manifold in which only the air flows and, the fuel is injected onto the intake valve. Since the intakemanifolds transport mainly air, the supercharging effects of the variable length intake plenum will be dif-ferent from carbureted engine.

Engine tests have been carried out with the aim of constituting a base study to design a new variablelength intake manifold plenum. Engine performance characteristics such as brake torque, brake power,thermal efficiency and specific fuel consumption were taken into consideration to evaluate the effectsof the variation in the length of intake plenum. The results showed that the variation in the plenumlength causes an improvement on the engine performance characteristics especially on the fuel consump-tion at high load and low engine speeds which are put forward the system using for urban roads. Accord-ing to the test results, plenum length must be extended for low engine speeds and shortened as theengine speed increases. A system taking into account the results of the study was developed to adjustthe intake plenum length.

� 2010 Elsevier Ltd. All rights reserved.

1. Introduction

It is known that the design of engine components, measuringand control methodology of the operating parameters are veryimportant to improve the engine performance and emission char-acteristics. Effectively adjusting the operating parameters such asthe relative air–fuel ratio, spark timing, fuel injection timing, valvetiming, exhaust gas recirculation ratio and compression ratio in SIand CI engines at different engine operation conditions improvessignificantly the engine characteristics. The effects of such engineoperating parameters and their control technologies have beenstudied excessively by researchers and the product designers. Inengines, configuration of the intake system plays also an importantrole on the engine performance, and there are many experimentaland theoretical studies on the intake system and manifold design[1–6].

Intake manifolds consist typically of a plenum, to the inlet ofwhich bolts the throttle-body, with the individual runners feedingbranches which lead to each cylinder. Important design criteria

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are: low air flow resistance; good distribution of air and fuel be-tween cylinders; runner and branch lengths that take advantageof ram and tuning effects; sufficient (but not excessive) heatingto ensure adequate fuel vaporization with carbureted or throttle-body injected engines [7]. The intake system on an engine hasone main goal, to get as much air–fuel mixture into the cylinderas possible.

The intermittent or pulsating nature of the airflow through theintake manifold into each cylinder may develop resonances in theairflow at certain speeds. These may increase the engine perfor-mance characteristics at certain engine speeds, but may reduceat other speeds, depending on manifold dimensions and shape.Conventional intake manifolds for vehicles have fixed air flowgeometry and static intake manifold. With a static intake manifold,the speed at which intake tuning occurs is fixed. A static intakemanifold can only be optimized for one specific rpm, so it is bene-ficial to develop a method to vary the intake length/volume, sincethe engine operates over a broad speed range.

Variable length intake manifold technology uses the pressurevariations generated by the pulsating flow due to the periodic pis-ton and valve motion to produce a charging effect. Various designsfor variable intake geometry have met with varying degrees of suc-cess. The designs of the variable intake manifolds may be rather

1- Engine 7- Air flow meter

2- Hydraulic dynamometer 8- Muffler

3- Gravimetric fuel flow meter 9- Exhaust gas analyzer

4- Additional plenums 10- Distributor

5- Air surge tank 11- Fuel Injectors

6- Air flow meter probe (hot wire)

3

6 7

10

1

2

5

9

4

8

11

Fig. 1. A schematic layout of test setup.

Table 1

2240 M.A. Ceviz, M. Akın / Energy Conversion and Management 51 (2010) 2239–2244

complex and expensive to produce. Difficulty in servicing and alimited range of variable tuning may also be disadvantageous de-sign results of variable intake manifolds. Studies on the intakemanifold design by regulating the runner length/volume for higherengine performance, optimal fuel consumption and lower emis-sions have significantly increased in the last years. Some of thestudies carried out by researchers and engine manufacturers (i.e.Mazda, BMW, Audi) [8–11] change the intake runner length; how-ever, it is known that intake plenum affects seriously the chargingconditions [12–14].

Previous work [12] on the effects of intake plenum on some en-gine performance characteristics was carried out mainly on thecarbureted engine. The carburetor produces the fuel and air mix-ture needed for the operation of the engine and is coupled to theintake manifold which receives the mixture and distributes it tothe cylinders. Design of intake plenum is active on the quality ofair–fuel mixture homogeneity in carbureted engine. In the enginewith multipoint injection systems using electronically controlledfuel injectors has an intake manifold in which only the air flows.The fuel is injected directly into the intake ports and the systemdelivers a more evenly distributed mixture of air and fuel to eachof the engine’s cylinders, which improves power and performance.Engines with multipoint injection have a separate fuel injector lo-cated to each cylinder intake port. Such injection systems are idealfor complying with the demands made on the air and fuel mixtureformation system.

In this paper, the effects of intake plenum length/volume varia-tion on the engine performance were studied experimentally on aspark-ignited engine with multipoint injection systems using elec-tronically controlled fuel injectors. The results were used for thedesign studies of variable length/volume intake plenum. A newplenum length control system was produced and explained indetail.

Engine specifications.

Engine type Ford MVH-418, fuel injectedNumber of cylinders 4Compression ratio 10:1Bore (mm) 80.6Stroke (mm) 88Displacement volume (dm3) 1.796Maximum power 93 kW at 6250 rpmMaximum torque 157 Nm at 4500 rpmCooling system Water-cooled

2. Materials and methods

A schematic layout of the test setup used is indicated in Fig. 1.The engine test bed was explained in the previous studies of theauthor [12,15,16], which consists of a control panel, a hydraulicdynamometer and measurement instruments. The engine specifi-cation is summarized in Table 1.

The engine performance characteristics through the variouspoints were calculated as follows: the brake power (Pb) deliveredby the engine and absorbed by the dynamometer is,

Pb ¼ 2pnT10�3 ð1Þ

where n is the crankshaft rotational speed (rev s�1) and T is the tor-que (Nm).

The thermal efficiency of the engine is,

gth ¼Pb

Qð2Þ

Q is the total heat supplied by the fuel was calculated from,

Q ¼ CV _mf ð3Þ

where _mf is the fuel consumption (kg sn�1) and CV is the lower cal-orific value of the fuel (kJ kg�1).

The specific fuel consumption (sfc) is the fuel flow rate per unitpower output and calculated from,

sfc ¼_mf

Pbð4Þ

where _mf is the fuel consumption (g h�1) and Pb is the brake power(kW).

At the beginning of experiments, the engine was run at a nearthree-quarter opening position of the throttle valve in order to at-tain near maximum speed. After the engine reached the steady-state conditions, the first experiment was conducted with originalintake manifold. The engine was gradually loaded by the hydraulicdynamometer and test matrix consisted of eight speeds rangingfrom 1500 to 5000 rpm with 500 rpm steps for each plenum addi-tion operation. The experiments were repeated with separately16 mm (40 cm3), 32 mm (80 cm3), 48 mm (120 cm3) and 64 mm(160 cm3) plenum addition at the same engine speeds that wereattained by loading hydraulic dynamometer. The additional ple-nums had the geometries suitable for entrance of the original in-take manifold, and located among the throttle valve and intakemanifold plenum.

3. Results and discussion

Figs. 2–5 show the effect of the plenum length on the engineperformance characteristics; thermal efficiency, specific fuel con-sumption, torque and brake power, respectively. It can be seenfrom Fig. 2 that the highest engine thermal efficiency is observed

0.17

0.19

0.21

0.23

0.25

0.27

0.29

0.31

1000 1500 2000 2500 3000 3500 4000 4500 5000 5500

The

rmal

Eff

icie

ncy

(-)

Engine Speed (rpm)

No addition

16 mm plenum addition

32 mm plenum addition

Fig. 2. Variation of thermal efficiency with engine speed for three different intake plenum volumes.

250

300

350

400

450

500

1000 1500 2000 2500 3000 3500 4000 4500 5000 5500

Spec

ific

Fue

l Con

sum

ptio

n (g

/kW

.h)

Engine Speed (rpm)

No addition

16 mm plenum addition

32 mm plenum addition

Fig. 3. Variation of specific fuel consumption with engine speed for three different intake plenum volumes.

20

30

40

50

60

70

80

90

1000 1500 2000 2500 3000 3500 4000 4500 5000 5500

Bra

ke T

orqu

e (N

.m)

Engine Speed (rpm)

No addition

16 mm plenum addition

32 mm plenum addition

Fig. 4. Variation of brake torque with engine speed for three different intake plenum volumes.

M.A. Ceviz, M. Akın / Energy Conversion and Management 51 (2010) 2239–2244 2241

at 32 mm plenum addition up to 3000 rpm. Improvement in theengine thermal efficiency was especially at lower engine speeds.At the experiments with the original engine manifold, engine ther-mal efficiency was 27.4%, whereas it increased to 27.9% and 30.9%for 16 mm and 32 mm plenum addition at 1500 rpm, respectively.There was also an increase in the engine thermal efficiency atthe experiments carried out by 16 mm plenum addition up to3000 rpm.

The highest engine thermal efficiency was attained by using16 mm plenum addition at about the engine speed range of3000–4000 rpm. As the engine speed increases, the higher enginethermal efficiency was attained at lower length of intake plenum.It is necessary to shorten of intake manifold length as the enginespeed increases because of the increase in the flow frequency asdiscussed in introduction section. The results of this study agreedwell with early studies [8–11,17], which were about the effects

10

12

14

16

18

20

22

1000 1500 2000 2500 3000 3500 4000 4500 5000 5500

Bra

ke P

ower

(kW

)

Engine Speed (rpm)

No addition

16 mm plenum addition

32 mm plenum addition

Fig. 5. Variation of brake power with engine speed for three different intake plenum volumes.

2242 M.A. Ceviz, M. Akın / Energy Conversion and Management 51 (2010) 2239–2244

of intake runner length. At high engine speeds as 4500–5000 rpm,the original engine intake manifold must be used because of thehigher thermal efficiency as seen from Fig. 2. It can be concludedfrom these figures that it is important to use the variable length in-take manifold plenum especially on urban and suburban areas(roads) with the frequent stops and acceleration at startingconditions.

Fig. 3 presents the specific fuel consumption characteristicswith the engine speeds. It can be seen from this figure that the fuelconsumption per engine power output was the lowest for theengine speed range of 1500–3000 rpm by using 32 mm plenumaddition, and for 3000–4000 rpm range by using 16 mm plenumaddition. The higher engine speeds, it is necessary to use the origi-nal engine manifold.

Figs. 4 and 5 present the engine brake torque and brake powercharacteristics with different engine speeds. At original engine ple-num experiments, the engine brake torque was 80.7 Nm, whereasit increased to 84.2 Nm for 32 mm additional plenum experimentsat 1500 rpm. However, there was no significant variation on theengine torque for higher speeds from 2500 rpm. Engine brake tor-que and brake power are controlled with the fuel injection strate-gies of the engine electronic control unit by measuring someoperating parameters. In this study, the experiments were carriedout at the same engine speeds, but at the different load of hydraulicdynamometer. Increase in the plenum length affected the amountof fresh fuel–air charge, and especially at lower speeds, to producethe same level of engine brake power, the engine control unit con-sumed less fuel because of the low engine load at the same engine

0.17

0.19

0.21

0.23

0.25

0.27

0.29

0.31

1000 1500 2000 2500 3000

The

rmal

Eff

icie

ncy

(-)

Engine S

No addition

16 mm plenum ad

32 mm plenum ad

48 mm plenum ad

64 mm plenum ad

Fig. 6. Variation of thermal efficiency with engine s

speeds. Consequently, dominant effect was observed on theparameters about the fuel consumption.

Figs. 6 and 7 present thermal efficiency, specific fuel consump-tion characteristics including the effects of much longer length ofintake plenum, as 48 mm and 64 mm (120 cm3 and 160 cm3).While the engine performance characteristics improved by using32 mm additional plenum especially at lower engine speeds, a re-verse effect appeared at the experiments carried out by using48 mm plenum addition, and this effect increased at 64 mm ple-num addition conditions for all engine performance characteristics.

The experimental studies showed that the variation in the ple-num length was not effective on engine exhaust emissions. How-ever, the decrease in the fuel consumption per engine poweroutput decreases the total production of harmful exhaust emis-sions. The original intake manifold and its plenum of the engineused in the experimental studies were designed for high poweroutput at high engine speed. Therefore, using the extended plenumwas useful for lower engine speeds. However, it can be concludedthat the results will be different for a new designed intake mani-fold, especially with a shorter length of intake plenum.

Fig. 8 illustrates a general views of the designed intake manifoldassembly which communicates the throttle valve and intake man-ifold with a movable plenum volume. Design criteria of the pro-duced system were determined by using the results of this study.The throttle valve section moves linearly in response to drive sys-tem to define an effective plenum length. Flexible section accom-modates the difference in length. The data acquisition card on apersonal computer measures continuously the engine speed from

3500 4000 4500 5000 5500

peed (rpm)

dition

dition

dition

dition

peed for five different intake plenum volumes.

250

300

350

400

450

500

1000 1500 2000 2500 3000 3500 4000 4500 5000 5500

Spec

ific

Fue

l Con

sum

ptio

n (g

/kW

.h)

Engine Speed (rpm)

No addition

16 mm plenum addition

32 mm plenum addition

48 mm plenum addition

64 mm plenum addition

Fig. 7. Variation of specific fuel consumption with engine speed for five different intake plenum volumes.

Runner

Engine

Plenum

Flexible section

Throttle valve

Drive module

A

Drive module

Throttle valve

Engine

Plenum

Runner

Runner

Flexible section

Engine

B

C

Fig. 8. (A) Front, (B) top and (C) solid view of intake manifold assembly.

M.A. Ceviz, M. Akın / Energy Conversion and Management 51 (2010) 2239–2244 2243

engine shaft encoder. The drive system actuates the throttle valvesection based on the engine speed information from data acquisi-tion card. In operation at low speeds, the throttle valve section is

driven to extend the flexible section to increase the length betweenplenum and throttle valve. As the engine speed increases, thethrottle valve is driven to shorten the flexible section. The systemtherefore provides a cost effective variable intake manifold plenumwhich will operate with different types of engines.

4. Conclusions

From the results of this study, the following conclusions can bededuced:

1. The intake manifold plenum length/volume is highly effectiveon engine performance characteristics especially with the fuelconsumption parameters for SI engines with multipoint fuelinjection system. The engine performance can be improved byusing continuously variable intake plenum length.

2. Favorable effects of the variable length intake manifold plenumappeared at high load and low engine speeds. Therefore, vari-able length intake manifold plenum is useful especially onurban and suburban areas (roads) with the frequent stops andacceleration at starting conditions.

3. It is necessary to determine the length of additional plenumcomponents for another engine and intake system with sensi-tive experimental studies.

Acknowledgement

This work has been supported by The Scientific and Technolog-ical Research Council of Turkey (TUBITAK, Project No. 107M018).

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