Combustion characteristics of intake port injection type hydrogen fueled engine

Pergamon ht. J. Hydrogen Energy, Vol. 20, No. 4. pp. 31 32:. 199.1

Copyright (‘ 1995 International Association for Hydrogen Energ) Elsevicr Science Ltd

0360-3199(94)ooo52-2 Printed III Great Britam. All rights reserved 0360 3199iYS ‘;9.si1 -t 0.00

COMBUSTION CHARACTERISTICS OF INTAKE PORT INJECTION TYPE HYDROGEN FUELED ENGINE

S. J. LEE,* H. S. YI,* and E. S. KIM? *Graduate School, Department of Mechanical Engineering, Seoul National University, Seoul, 151-742. Kore.t

t Department of Mechanical Engineering, Seoul National University. Seoul. I51 -174. Korea

(Receioed ,for puhliration 29 April 1994)

Abstract-This paper describes the experimental results on a hydrogen fueled single cylinder engine to study the characteristics of a solenoid-driven intake port injection type hydrogen injection valve. In experiments, the fuel-ail equivalence ratio was varied from the lean limit at which stable operation was guaranteed to the rich limit at which flash-back occurred and spark timing was also changed. As a consequence, a hydrogen intake port injection system can be easily installed on a spark ignition engine only with simple modification and the flow rate of hydrogen supplied can also be controlled conveniently. In this case, the most serious problem is flash-back and it can be suppressed by accurate control of injection timing and elimination of hot spots on the surface of the combustion chamber

BMEP Brake mean effective pressure BSFC Brake specific fuel consumption BTDC Before top dead center cov Coefficient of variation IMEP Indicated mean effective pressure MBT Minimum spark advance for best torque TDC Top dead center S/T Spark timing WOT Wide open throttle

NOMENCLATURE

INTRODUCTION

In recent days, the importances of environment and energy are emphasized and among various energy sour- ces, the fuels for automotive use are drawing attention as they are closely related with our daily life. The fossil fuels which are widely used nowadays have some serious problems. One of these is the limit in reserve, the second problem is they cannot be recycled and another is that they produce many kinds of pollutive emissions. There- fore, various researches on alternative fuels have been carried out to substitute fossil fuels. Among them, hydrogen has the outstanding advantages of wide flam- mable range and no production of unburned hydrocar- bon and carbon monoxide if there are no lubricants in the combustion chamber.

In order to adopt gaseous hydrogen as the fuel for an internal combustion engine, a lot of research has been carried out on hydrogen supply system [l], combustion characteristics [2-S], and so on, and many areas of research are concerned with the adoption of in-cylinder

type injection system for high pressure hydrogen [3-61. This type of injection system can eliminate the possibijity of flash-back into the intake pipe and can produce more power than an intake port injection system. But this system has a very complicated structure and greater durability problem. To overcome the disadvantages of the high pessure in-cylinder injection system, a low pressure intake port injection system was tried with timed injection [7,8].

In this study, an intake port injection system was constructed and installed on a single cylinder en&e prior to the development of in-cylinder injection system using a solenoid as the driving source of the injection valve. In order to minimize the possibility offlash-back occurrence, injection timing of the hydrogen injection valve was set within the duration of intake valve opening, Namely, the hydrogen is supplied while the intake valve is open, so that the hydrogen injected into the intake port could be induced into the combustion chamber as much as poss- ible. With this system, combustion characteristics of hydrogen combustion in the internal combustion engine were investigated and flash-back phenomena were also studied by measuring the intake and exhaust pressures simultaneously.

EXPERIMENTS

Experimental apparatus

Experimental apparatus was construated as shown in Fig. 1. The air intake system of a sit@ engine was modified for hydrogen supply and the hydrogen is injected to the back of the intake valve. Tables 1 and 2

317

318 S. J. LEE et al.

A : single cylinder engine G : air surge tank

B : dynamometer H : hydrogen injection valve

C : crankangle detector I: hydrogen flowmeter

D : pressure transducer J: hydrogen storage vessel

E : combustion analyzer K : gas chromatography

F : personal computer L : integrator

Fig. 1. Experimental setup for hydrogen fueled single cylinder engine.

Table 1. Specifications of single cylinder engine Table 2. Specifications of hydrogen injection valve

Item Specifications Item Specifications

Type 4 cycle, water cooling, spark ignition Displacement (1) 0.488 Bore x stroke (mm) 85 x 86 Comnression ratio 8.5 : 1

1

Intake valve Open Close Open Exhaust valve Close

16” (BTDC) 54’ (ABDC) 52” (BBDC) 12” (ATDC)

Manufacturer Type Pressure rating Operating speed Timing precision Coil resistance Operating voltage

Response time

Servojet Products Inc. 2 way normally closed ball poppet

2.0 MPa max. 200 Hz

+ 25 p 1.6 iI 12 v

Open 3.0 ms Close 2.0 ms

represent the main specifications of the single cyclinder engine and the hydrogen injection valve used in the experiments, respectively. A hydrogen supply line was constructed as shown in Fig. 2, and two mass flowmeters with different measuring ranges were installed. During the experiments, one of them was selected according to the flow rate of hydrogen supplied. In order to measure the pressures of cylinder, intake pipe, and exhaust pipe, piezo-electric type pressure transducers were installed and the voltage signals from charge amplifiers were recorded by personal computer through SNUCAS (Seoul National University Combustion Analyzing System). Also an exhaust gas sampling line was installed to measure the concentration of nitrogen oxide and the temperatures of various points were measured.

Experimental procedure In experiments, engine speed was set at 1000 and 1500

rpm and fuel-air equivalence ratio was varied from the lean limit which guarantees stable operation to the rich limit at which flash-back occurs. In most cases, spark timing was adjusted to MBT timing by considering both BMEP and BSFC, and the throttle valve was fully opened through the experiments.

The beginning of injection was fixed to TDC of gas exchange process, that is 16” (crank angle) after the intake valve opening timing, and the duration of solenoid valve was varied according to the required amount of hydrogen at each fuel-air equivalence ratio. The supply pressure of hydrogen into the gas injection valve was set at 1.0 MPa.

COMBUSTION CHARACTERISTICS OF HYDROGEN FUELED ENGINE ? I ‘1

mass flowmeter

0-200SLM

from pressure regulator

hydrogen supply line

0-20SLM

check needle

from pressure regulator

Fig. 2. Schematic diagram of hydrogen supply line

hydrogen supply line

RESULTS AND DISCUSSIONS This section represents the results of the engine oper-

ating experiments and is divided into four parts. The first part is the comparison of hydrogen combustion with gasoline combustion at the same operating conditions. The next part represents the results obtained by varying the fuel-air equivalence ratio. The third part is on the effects of spark timing and the last part represents the results acquired in case of flash-back occurrence.

Comparison with gasoline combustion

Table 3 represents the comparison of experimental results from hydrogen fuel for intake port injection and gasoline fuel at 1500 ‘pm, WOT, and fuel-air equivalence ratio of 1.0. In the case of hydrogen, MBT timing is retarded to TDC compared with the case of gasoline, as the flame speed of hydrogen is much faster than that of gasoline. The volumetric efficiency of a hydrogen fueled engine is below 60% and is less than that of gasoline fueled engine by about 30%. This is because the hydrogen is injected into the intake port and is induced into the combustion chamber after being mixed with air. There- fore the equal amount of air that corresponds to the amount of hydrogen at fuel-air equivalence ratio of 1.0 is displaced, and it is about 30% of total volume.

Also, indicated mean effective pressure is lowered in the case of hydrogen due to the decrease in volumetric efficiency. Indicated thermal efficiency of hydrogen operation is somewhat higher than that of gasoline operation. The thermal efficiency of hydrogen operation is higher in the leaner range than that of gasoline operation, but near stoichiometric ratio, they appear similar to each other.

The COV,, of hydrogen operation, which is the measure of en&e operation stabihty, is 0.7 1% and that of gasoline operation is 1.58%. So the combustion of

Table 3. Comparison of experimental results from hydrogen for port injection system and gasoline (1500 rpm, WOT, MBT.

q5 = 1.0)

Item

MBT (deg. BTDC) Volumetric efficiency,

‘1, (%I

Hydrogen Gasoline

5 20 59.7 86.7

Indicated mean effective pressure, IMEP (MPa)

0.92 1.14

Indicated thermal efficiency, %h,i (%)

36.7 35.8

cov,,,, ( % 1 Cylinder peak pressure.

IL WP4

0.11 1.58 5.08 3.92

Flame development angle (deg.) 1.6 23.1 Rapid burning angle (deg.) 8.9 27.9 NO concentration (ppm kW - i) 856 ;7 1

hydrogen is more stable because of faster flame speed and shorter flame development angle. As COV is mainly affected by flame development angle, the shorter one provides the lower COV and the more stable operation.

The cylinder peak pressure of hydrogen operation is above 5.0 MPa and is higher than that of gasoline operation by more than 1.0 MPa. Owing to this high cylinder pressure, the amont of NO, emission increases and problems of noise and vibration occur. Thus high cylinder pressure and rapid pressure rise are serious disadvantages of hydrogen fuel.

The NO emission concentration of hydrogen aperation is 856 ppm kW- ’ and that of gasohne operation is 371 ppm kW- ‘. By means of faster flame speed and higher pressure rise rate, NO is generated in a large quantity and is frozen during the expansion stroke. ~n~.~y~r~~ fueied engine the reaction of NO into N, is terminated earlier.


0 I I I

0.2 0.4 0.6 0.8 1.0

fuel-air equivalence ratio

Fig. 3. BMEP as a function of fuel-air equivalence ratio at 1000 rpm, MBT, WOT.

Trend in fuel-air equivalence ratio variation Effects of spark timing

At an engine speed of 1000 rpm, the fuel-air equivalence ratio was varied from a lean limit of 0.32 to a rich limit of 0.95. Figure 3 shows the brake mean effective pressure as a function of the fuel-air equivalence ratio. As the fuel-air equivalence ratio is increased, BMEP increases almost linearly. But when the fuel-air equivalence ratio is greater than 0.80, BMEP begins to decrease slightly. From this, incomplete combustion or by-passing of unburned hydrogen can be inferred. As hydrogen is known to be easily ignited by a small amount of energy, the only possibility is by-passing of the remaining hydrogen in the intake port into the exhaust port during valve overlap. This can be checked by measuring the exhaust gas composition and concentration using gas chromato- graph. The authors’ previous study [9] has indicated that the unburned hydrogen was detected in the exhaust pipe above a fuel-air equivalence of 0.8 and the concentration is up to 10% at a fuel-air equivalence ratio of 1.0.

On a spark ignition engine, spark timing is a very important parameter which governs the entire combustion process. Therefore, experiments were carried out by changing the spark timing for fuel-air equivalence ratios of 0.43, 0.50 and 0.80, at engine speed of 1500 rpm.

The cylinder pressure along with crank angle is indicated in Fig. 4. In this case, fuel-air equivalence ratio is 0.50 and spark timing is changed from TDC to 27” BTDC. When spark timing is set at TDC, the pressure diagram is distorted and the combustion process begins after the piston starts moving downward. The peak pressure is about 2.5 MPa as a result of excessively retarded spark timing. As spark timing is advanced, the peak pressure increases and the crank angle at which peak pressure appears approaches TDC. When spark timing is 27” BTDC, the peak pressure is very high but the work produced from cycle does not increase any more,

5

4 ---.- Sfl= l&,-ID‘2

3

0 -180 -120 -60 0 60 120 180

crankangle (deg.)

Fig. 4. Cylinder pressure with crank angle at 1500 rpm, WOT, Fig. 6. IMEP and cylinder peak pressure variations with cycle Q = 0.50. number at 1500 rpm, 4 = 1.0.

spark timing (deg. BTDC)

Fig. 5. BMEP as a function of spark timing at 1500 rpm, WO’

2 B e a t t E

6

tt 1 I i m I # I I 1

70 80 90 100 110 120 130

cycle number

COMBUSTION CHARACTERISTICS OF HYDROGEN FUELED ENGINE !‘I

15OOrpm, WOT _ .,......

1 S/T=lS”BTDc 25th cycle @=l.O -

0 I I I

-180 0 180 360 540

crankangle (deg.)

I -A. I

0 I80 360 540

crankangle (deg.)

Fig. 7. Cylinder, intake, and exhaust pressure variations for 25th Fig. 9. Cylinder, intake, and exhaust pressure variationi for 1 10th cycle at 1500 rpm, WOT, 4 = 1.0. cycle at 1500 rpm. WOT. d, = I 0.

because the compression work done before TDC increases greatly and the increased amount of expansion work is below that.

Figure 5 represents the brake mean effective pressure as a function of spark timing at 1500 rpm for fuel-air equivalence ratio of 0.43,0.50 and 0.80. When the fuel-air equivalence ratio is 0.80, the BMEP shows the maximum value when the spark timing is near TDC and decreases as spark timing is advanced. In case of a fuel-air equivalence ratio of 0.50, the BMEP represents the maximum value when the spark timing is 9” BTDC, so it can be judged as the MBT spark timing. If fuel-air equivalence ratio is decreased, the peak does not appear clearly and the increment in BMEP due to advanced spark timing is small. If spark timing is advanced excessively, the cylinder peak pressure increases and consequently NO emission concentration increases, therefore in case of vehicle application, spark timing shall

0 I I I

.I80 0 180 360 540

be retarded slightly from MBT timing m order to accomplish the aims of low NO concentration level and high power output simultaneously.

Flash-back

In the case of an intake port injection type hydrogen fueled engine, flash-back usually occurs in a high load range if hydrogen remains in the intake system. That is, flash-back occurs easily as the fuel-air equivalence ratio is near stoichiometry or as spark timing is advanced, this is because the wall temperature of combustion chamber is high and there exists the energy source for ignition.

The history of IMEP and cylinder peak pressure along with cycle number at 1500 rpm is indicated in Fig. 6 for a fuel-air equivalence ratio of 1.0 and spark timing of 15” BTDC. At about the 100th cycle after advancing the spark timing from TDC to 15” BTDC, flash-back begins to occur. At the first stage, IMEP isdecreased but cylinder

n

- 25th

f-----l

: 2. .~.. *A’ : 15OOrpm.WOT . . . . . . .._ ,&)a / o

-.-.-,l()* i .$ j \ S/r=15 BTCC

----- 115th .i $. .i /l-----A:

t

j'!. @=l,O i

.' : I ..; .i

,,"

!;.:.::;i,

.I '

..i'. . ..i._

I

/. :,\ . -1 \

,.I ,'; , '.. 4

d' \

.e. * ; . .: *. .i

i , , : '-__ .- . . , i-

---+------

:lSO ,120 -60 0 60 120 180

crankangle (deg.) crankangle (deg.)

Fig. 8. Cylinder, intake, and exhaust pressure variations for 100th Fig. 10. Cylinder pressure vanation for 25th, 100th cycle at 150+ cycle at 1500 rpm, WOT, 4 = 1.0. t-pm. WOT. qb = 1.0


peak pressure remains at the same level. After a few cycles, cylinder peak pressure is also decreased almost to motor- ing pressure and then the normal combustion process is recovered. The above phenomenon is repeated three times and then the engine is stopped.

In order to investigate the process of flash-back occurrence in detail, intake, exhaust and cylinder pressures were measured at the same time. Figure 7 shows each pressure at the 25th cycle. This is the case of normal combustion and shows typical results of pressure variation. Figure 8 indicates the 100th cycle, which is the early stage of flash-back. At this cycle, cylinder pressure begins to rise at 80” BTDC. This means that hydrogen mixture is ignited prior to the spark timing, therefore the cylinder peak pressure remains at a high level because the burned gas is compressed by the piston but the work produced during the cycle is almost zero due to the increased compression work. Then the intake pressure shows a sharp rise at the end of cycle. This is the late part of intake valve opening duration, and an induced mixture is ignited by the hot spot generated after pre- ignited combustion.

Figure 9 is the late stage of flash-back, that is the 115th cycle. Pre-ignition in the combustion chamber after intake valve closing and ignition of induced mixture during intake valve opening are followed by flash-back into the intake pipe after intake valve closing. In this case, the combustible mixture has been completely burned in the intake pipe so that no power can be generated in the cylinder. Consequently the engine stops after a few cycles. Figure 10 represents the cylinder pressure of the 25th, lOOth, 1 lOth, and 115th cycles. This plot shows the process of flash-back clearly.

CONCLUSIONS

An intake port injection type hydrogen supply system using a solenoid-driven gas valve was constructed and engine experiments were carried out with this system to investigate the combustion characteristics of hydrogen fuel, including the flash-back phenomena. As a result of this study, the following conclusions could be obtained.

With the hydrogen supply system adopting a solenoid- driven gas valve, the engine was operated successfully and the amount of hydrogen supplied could be controlled very easily by changing the duration of the solenoid

driving signal. But severe flash-back was observed near stoichiometric fuel-air equivalence ratio. The cause of flash-back is thought to be a hot spot, such as a lubricant deposit or spark plug rather than the high temperature residual gas itself. The flash-back initiates from the pre-ignition during the compression stroke, and then proceeds to the ignition of the intake mixture. Finally the flame propagates into the intake pipe and as no combustible mixture can enter the combustion chamber, the engine is stopped.

In order to operate the engine at a higher engine speed and also to decrease the range in which flash-back occurs in the fuel-air equivalence ratio, the injection timing should be controlled accurately considering the move- ment delay of the solenoid. The intake port injection system of hydrogen using a solenoid-driven gas valve can be easily adopted on a conventional spark ignition engine with only simple modifications in contrast to the in- cylinder high pressure injection system.

1.

2.

3.

4.

5.

6.

I.

8.

9.

REFERENCES L. M. Das, Fuel induction techniques for a hydrogen operated engine. Inc. J. Hydrogen Energy 15, 833-842 (1990). M. R. Swain, J. M. Pappas, R. R. Adt, Jr. and W. J. D. Escher, Hydrogen-fueled automotive engine experimental testing to provide an initial design-data base. SAE Paper 810350(1981). H.S. Homan, P.C.T. deBoer and W.J. McLean, The effect of fueld injection on NO, emissions and undesirable combustion for hydrogen-fueled piston engines. SAE Paper 780945 (1978). T. Fukuma, T. Fujita, P. Pichainarong and S. Furuhama, Hydrogen combustion study in direct injection hot surface ignition engine. SAE Paper 861579 (1986). M. Takiguchi, P. Pichainarong, T. Matsushita and S. Furuhama, Characteristics of combustion pressure vibration in hydrogen fuel injection hot surface ignition engine. SAE Paper 871611 (1987). K. Koyanagi, M. Hiruma, I$ Hashimoto, K. Yamane, and S. Furuhama, Low NO, emission automobile liquid hydrogen engine by means of dual mixture formation. SAE Paper 930757 (1993). J. Levi and D. B. Kittelson, Further studies with a hydrogen engine. SAE Paper 780233 (1978). H. B. Mathur and L. M. Das, Performance characteristics of a hydrogen fuelled S.I. engine using timed manifold injection. Int. J. Hvdroaen Enerav 16. 115-127 (1991). S. J. Lee,‘W. ii. Cho, i’S. ?oo and E.‘S. Kim, Estimation of air-fuel ratio in hydrogen fueled engine. SAE Paper 931944 (1993).

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Combustion characteristics of intake port injection type hydrogen fueled engine