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In this research, the operating characteristics of a spark-ignition engine using ammonia were evaluated. Different compression ratios and two pistons with different squish velocities were used. Results show that the combustion duration was shortened with high compression ratio and high squish piston, and the stable operation range of the engine was expanded. BMEP and brake thermal efficiency did not change significantly among the stable operation range for variations of compression ratio, squish velocity. Due to the reduction effect of unburned ammonia, NOx emissions decreased when ammonia mole fraction increased. Most of the unburned ammonia was emitted from the quenching layer.

Atomization characteristics of an ultrasonic fuel injector using a micro nozzle array were improved by change of horn geometries. Micro nozzles whose exit diameter d = 3 µm are mounted on a thin metal film, and the number of micro nozzles was varied from 2.0 × 104 to 1.2 × 105. Gasoline is periodically pushed out from the micro nozzles at frequencies from 62 to 65 kHz. A disk type PZT (Lead zirconium titanate) is used as an ultrasonic oscillator, and the oscillation is amplified by an axi-symmetric step-type horn. The oscillation amplitude is proportional to the area ratio of the horn. The number of micro nozzles increases with the increase in the small end diameter of the horn, while the oscillation amplitude decreases at the same time. In order to increase the fuel flow rate, the horn small end diameter Ds was varied from 10.5 to 25 mm, while the large end diameter is fixed at 30 mm.

In a boat two-stroke two-cylinder engine, SC-port fuel injection of CNG was applied at running condition in comparison with the fuelling with a gas-mixer. Three methods of tests were employed; operation at a test-bench, at an anchored condition and on a running boat. In a lower engine speed, the beneficial effect of higher thermal efficiency was obtained, while in higher engine speed range especially at the running condition, it has the inverse effect of lower thermal efficiency. It is based on the limited range of lower injection rate of the fuel injectors, and thus the fuel injection rate of this type of fuel injectors has a key role of developing the technology of the SC-port injection.

Performance of a CNG (Compressed natural gas) two stroke cycle S.I. engine using intermittent low pressure fuel injection from scavenging ports is investigated experimentally. The test engine is a two cylinder, 398 cm3, two stroke cycle spark ignition engine. Gaseous fuel injectors are attached at the engine block, and a CNG is injected into the scavenging passage through a fuel injection pipe. The fuel injection pressure is set at 0.255 MPa, and the fuel is injected intermittently during the scavenging process. The length and tip geometry of the fuel injection pipe are varied, and the effect on the engine performance is investigated. Using the scavenging port fuel injection, the BSFC is reduced by 25 %, and the lean burn limit extends from λ = 1.2 to 1.46, at the maximum. The peak of the NOx emission shifts to leaner side, and the THC emission is reduced by 47 % at the maximum.

The most serious problem in a 2-stroke spark-ignition engine is poor trapping of fresh charge. To solve this problem, a scavenging-port injection was applied, and a fuel injection pipe (FIP) was installed at the injector tip. In a previous study, it was shown that the BSFC and emission characteristics were drastically improved. In the present study, effect of increase in the fuel injection rate was investigated. It is shown that the BSFC and the THC emissions improved at high engine speeds, while they slightly deteriorate at low engine speeds. The increase in the fuel injection rate is effective particularly at high engine speeds, where the scavenging duration becomes shorter.

Effects of horn geometry on the atomization characteristics of an ultrasonic fuel injector using a micro nozzle array were investigated experimentally. Micro nozzles whose exit diameter d = 3 μm are mounted on a thin metal film. The number of the micro nozzles is from 2.0 × 104 to 1.2 × 105. Using an ultrasonic oscillator, gasoline is periodically pushed out from the micro nozzles at a frequency from 62 to 65 kHz. A disk type PZT (Lead zirconium titanate) is used as an ultrasonic oscillator, and the oscillation is amplified using a step-type horn. The input voltage to the PZT is varied from 0 to 200 V. To increase the fuel flow rate, the horn small end diameter DS is increased from 10.5 to 25 mm, while the large end diameter is fixed at 30 mm. To prevent forming a liquid film on the micro nozzle array, gutters are machined on the small end of the horn. It is shown that the SMD (Sauter mean diameter) of the spray is almost uniform around 10 to 14 μm.

This study presents the possibility of realizing better thermal efficiency in a spark-ignition engine with over-expansion cycle. The test engine with the displacement volume of 649cc was used together with four kinds of expansion ratios (geometric compression ratio) from 10 to 25, and four sets of intake valve closure timings from 0 to 110 ° C.A. ABDC. In previous studies, the indicated thermal efficiency reached 48% However, there was a problem that the maximum output was reduced to almost half compared with the conventional engine, since the effective displacement volume was decreased with decreasing the substantial compression ratio (εc). As a method of solving this problem, supercharging was applied by using compressed air supplied from an external compressor.

Injection rate measurement of an automotive gaseous fuel injector was carried out by use of a one-dimensional pipe flow. A production gaseous fuel injector for an NGV (Natural gas vehicle) was used, which is for an intake port fuel injection. The injection pressure was set at 255 kPa(g), and the injection duration was varied from 3.4 to 20 msec. Nitrogen gas was used as the test gas. The test gas was injected into a pipe from the injector, and the static pressure history was acquired with a piezoelectric pressure transducer. One-dimensional, compressible, inviscid, adiabatic flow was assumed, and the instantaneous mass flow rate inside the pipe was estimated. By integrating the injection rate during the injection duration, the total amount of mass flow per one stroke was calculated. Calibration test was carried out by use of a pressure vessel, from which the total mass flow during one stroke was estimated.

Characteristics of compressed natural gas (CNG) direct injection auto-ignition were investigated experimentally. A rapid compression machine (RCM) with the compression ratio of 10 was used. The diameter and thickness of the combustion chamber are 80 mm and 20 mm, respectively. After the compression start, fuel was directly injected with a single hole injector at the injection pressure of 7.0 MPa, and auto-ignition takes place. The fuel injection timing was varied from 50 ms to 60 ms from the compression start. Two kinds of natural gasses were tested; 12A (CH4: 99.1 %) and 13A (CH4: 86.3 %, C2H6: 5.2 %, C3H8: 1.9 % and others). A glow plug was installed in the cylinder in order to assist the ignition, which was set at 30 mm downstream from the fuel injector nozzle exit. Two kinds of auto-ignition processes were observed. For CNG 12A, auto-ignition always takes place after the end of the fuel injection. The ignition delay is relatively long (40 to 80 ms) and the fluctuation is large.

This paper presents the effect of application of scavenging-port injection to a two-stroke two-cylinder boat engine fueled with a compressed natural gas (CNG). Experiments were carried out at a constant speed of 3000 rpm and WOT condition with varying excess air ratio in lean region. A CNG injector for a production automobile engine was utilized and installed into the scavenging ports. Comparison was made with homogeneous charge operation using a gas mixer. By applying the scavenging-port injection, unburned-fuel in the exhaust gas was reduced close to half which must be due to the reduction of fuel short-cutting during the gas exchange process. The lean-burn limit was extended from the excess air ratio of 1.21 to 1.57. The maximum decrease of BSFC reached to 25 %. This suggests that stratified-combustion could be realized in its lean-burn region.

Characteristics of premixed charge compression ignition (PCCI) Diesel combustion were investigated experimentally. In a PCCI engine, the operatable range is limited by the cyclic variation at low loads and the intensive knock at high loads. In the present study, effects of compression ratio on the characteristics of the PCCI combustion are investigated experimentally. The compression ratio was varied from 18.8 to 14.8. For the early injection timing, the high load operation limit is extended from BMEP = 0.22 MPa to 0.40 MPa. At the same time, the minimum BSFC for the early injection timing decreases from 330 g/kWh to 230 g/kWh.

This paper presents two factors for improving the performance and emissions characteristics in HCCI diesel combustion, one is reducing compression ratio and another is changing the injector position. In a previous study, it was shown that HCCI diesel combustion could be realized by utilizing a hollow-cone spray with normal injection pressure. However there remained two major problems of engine instability and increase in BSFC (decrease in brake thermal efficiency). By reducing the compression ratio from 18.8 to 16.8, the engine stability was much improved to the level of conventional diesel combustion and the increase in BSFC became almost half, which was mainly due to the change of combustion phasing. In addition to this, application of 5 mm inside position of the injector realized almost no penalty of BSFC at higher load condition.

This paper presents a further investigation into the effect of more-expansion cycle in a spark-ignition engine. On the basis of the results obtained in the previous studies, several combinations of late-closing (L.C.) of intake valve and expansion ratios were tested using a single-cylinder production engine. A large volume of intake capacity was put into the intake manifold to simulate multi-cylinder engines. With a large intake capacity, L.C. can decrease the pumping loss and thus increase the mechanical efficiency. Increasing the expansion ratio from 11 to 23.9 with L.C. application can produce about 11% improvement of thermal efficiency which was suggested to be caused by the increased cycle efficiency. The decrease of compression ratio from 11 to 5.5 gives little effect on the thermal efficiency if the expansion ratio could be kept constant.

The objective of the present study is to clarify the effect of early-closing of an intake-valve on the engine performance in a spark-ignition engine. For the first step of the study, under natural aspirating condition, four sets of expansion ratio pistons of 11, 16, 20 and 22 were prepared for two kinds of camshaft, one is, original and the other is geometrically half early-closing.. The obtained performance data and the indicator pressure records were analyzed. It was shown that up to 7 % of improvement in the thermal efficiency can be realized over a wide range of operating condition. This is considered to be mainly caused by the effect of the increased-expansion cycle. The increased-expansion effect can be estimated to be about 1.4 which almost corresponds to the geometrical inlet-valve closure timing. However, this value is not consistent with the measured volumetric efficiency which was almost half the value associated with original timing.

This paper presents the effect of fuel atomization at an intake manifold on the combustion characteristics of a spark-ignition engine. Four sets of fuel-supply devices were tested which have much difference in atomization characteristics in terms of the mean droplet size ranging from wall film to 7 um S.M.D. Over the whole operatable range of mixture strength, the fuel atomization did not give any effect on BMEP, BSFC and volumetric efficiency, but had an effect on the engine stability at lean operation limit under most operating conditions. This atomization effect was shown to be systematically characterized by mapping on the ignition timing and A/F plane. The appearance of partial-burn limit on the map was successfully verified by the combustion analysis using a correlation procedure on cycle by cycle basis.

The swirl and axial components of gas velocity in the disk type combustion chamber of a fired and motored spark ignition engine were measured using a fiber-optic laser Doppler Anemometer (LDA). The engine was operated at a speed of 1500 rpm, a volumetric efficiency of ηυ = 0.5, an equivalence ratio ϕ = 1.4 and with an ignition timing of θig = 30°BTDC (MBT condition). The gas velocities at 9 points on a diameter at mid-height of the combustion chamber were processed by the cycle-resolved frequency discrimination method. The bulk (mean) velocity was determined by frequency components lower than a cut-off frequency of 667Hz. The flame propagation pattern was detected by ionization probes set at 17 points on the piston. The results indicate significant differences in flow characteristics between motored and fired conditions during the combustion period.

This paper presents the fuel atomization effect of a fuel supply system on the lean burn characteristics of a spark-ignition engine and its mechanism. The fuel supply system can realize extremely different two state of atomization, i.e., wall-film of fuel flow and ultra-fine spray (less than 7 um S.M.D. by Malvern measurement). For the first step of the study, the atomization effect is examined under steady operation; several operating parameters including cyclic variability are expressed against the A/F over the wide range of operating condition. Within the operation limits, the fuel atomization does not affect any parameters, while it gives pretty much influence on the lean operation limit. Furthermore, this influencing behavior strongly depends on the throttle valve position and its opening.

By using an inside visible carburettor, effects of high voltage application to the injected fuel on its behaviour and engine performances are investigated. At first five electrode arrangements around the venturi are examined to clearify the charging mechanism on the injected fuel and its effect on the fuel atomization. The experimental results show that when induced charging, corona charging and electrostatic force are effectively applied to the injected fuel, its atomization is remarkably improved. The diameter of fuel droplets monotonously decreases with increase of applied voltage and the effect is more distinct when the induced air velocity is low. Firing engine test is also carried out and it is revealed that when the throttle valve opening is large, the application of voltage considerably spreads the combustible range toward leaner side. Cyclic variation is reduced and startability is improved by the charge under the severe operating condition.

The purpose of this study is to reveal the ignition assistance mechanism in an alcohol fueled diesel engine. A motored two stroke cycle engine with a ceramic hot plug is motored, and one shot of spray is injected into the combustion chamber. Ignition lags are measured and splitted into physical and chemical lags by means of a statistical technique presented by S. Kumagai. High speed direct photographs are also taken. From the experimental results, it has been found that there are three kinds of hot surface temperature regions. In the low temperature region the mean value of ignition lags, the physical and chemical lags decrease exponentially with increasing the hot surface temperature. These decreasing behaviours are expressed by Arrhenius type equation. The activation energies of these three kinds of lags have the same value. In the higher temperature region the ignition lags are not affected by the hot surface temperature. Between these two regions a transient region is recognized.

The purpose of this study is to reveal the effect of use of W/O emulsified fuel without additives on DI diesel combustion. The combustion pattern, which means the ratio of fuel mass burned in the premixed (or the diffusion) combustion period to the overall supplied fuel mass, is varied by changing the injection timing and the intake manifold pressure. The exhaust emissions, such as particulates, NOx and CO, are measured. By analyzing the indicator diagrams, ignition lags are also measured. Contrary to the results of the other studies, NOx is hardly reduced by using the emulsified fuel, although it does not increase. While the particulate emission is considerably affected, remarkable changes in S.F.C. and the exhaust gas temperature are not recognized. With decreasing the fuel mass fraction burned in the prernixed combustion (spontaneous ignition) or the intake manifold pressure, the effect of the emulsification on particulate emission turns from the promotion to the suppression.