Published papers

The Homogeneous Charge Compression Ignition (HCCI) engine is possible to achieve high thermal efficiency and low emissions. It is necessary for practical use of HCCI Engine to establish the index of fuel auto-ignition, because of diversification of configuration and fuels. The purpose of this study is to obtain fundamental knowledge about the relation between shock tube and engine, and examine the behavior of fuel auto-ignition under the experimental trial.

In the HCCI (Homogeneous Charge Compression Ignition) engines, inhomogeneity in fuel distribution and temperature in the pre-mixture exists microscopically and has possibility to affect the ignition and combustion process. In this study, the effect of charge inhomogeneity in fuel distribution on the HCCI combustion process was investigated. Pressure profiles were measured and two dimensional chemiluminescence images were captured by using a framing camera with a 4-stroke optically accessible engine in order to understand the spatial distribution of the combustion. DME (di-methyl ether) was used as the test fuel. By changing the way of mixing air and fuel in the intake manifold, inhomogeneity in fuel distribution in the pre-mixture was varied. The result shows that luminescence is observed in a very short time in a large part of the combustion chamber under the homogeneous condition, while luminescence appears locally with considerable time differences under the inhomogeneous condition. It is also shown that the local luminescence durations are almost the same under both conditions. Methyl Ether, Chemiluminescence, Radical

The past researches clarify the advantages and the disadvantages of HCCI Engine. In this paper, the conditions such as the amount of intake fuel and EGR gas, that can realize the operation, are investigated by using the past experimental data and the numerical analysis. On the basis of this, actually the engine is designed and tested. In addition, EGR gas is controlled by two ways, one is changing the exhaust tappet clearance and another is using the new cam that has two ledges in exhaust. The effect of the difference of the residual ways is investigated.

The past researches clarify the advantages and the disadvantages of HCCI Engine. In this paper, the conditions such as the amount of intake fuel and EGR gas, that can realize the operation, are investigated by using the past experimental data and the numerical analysis. On the basis of this, actually the engine is designed and tested. In addition, EGR gas is controlled by two ways, one is changing the exhaust tappet clearance and another is using the new cam that has two ledges in exhaust. The effect of the difference of the residual ways is investigated.

Turbo-charging was applied to HCCI engine to increase the output. The test engine is vertical, water-cooled 4cylinder one with 98mm bore, 110mm stroke and 3.3litter displacement. It was modified to suit the HCCI operation. As the attainment, 43.2% brake thermal efficiency, 0.98MPa brake mean effective pressure, and 13.8ppm NOx emission have been gained.

In HCCI engines, the inhomogeneity in fuel concentration in the pre-mixture gas makes the combustion duration longer and the rise of in-cylinder gas pressure moderate when the fuel that has large heat release in low temperature reaction is used. In this paper, we observe chemiluminescence images on HCCI combustion by the 4-stroke optically accessible engine using DME that has large heat release in low temperature reaction and n-Butane that has small one in low temperature reaction.

In order to clarify the reason why the NOx emissions factor becomes higher with vehicle acceleration at intersections etc., two freight vehicles of different emission model years, equipped with EGR systems for reduction of NOx, were tested by an on-board NOx measurement system. Higher NOx emissions factors were observed at vehicle starts in lower-gear operations for each vehicle though the total NOx mass emissions of the later model vehicle were less. Larger NOx mass emissions were clearly observed in the engine operation area of lower engine speed and load in real traffic conditions though the NOx mass emissions in steady state conditions was less. NOx emissions characteristics were analyzed in view of engine torque, NOx mass emissions, and the EGR rate, and considering the rate of engine speed change. It was found that lower-gear operations made the rate of engine speed change higher and also the EGR rate lower resulting in higher NOx emissions. This seems to be one of the factors to engender the intensive NOx pollution at roadsides.

A small and light HCCI engine fuelled with DME has been developed. This engine uses a two-stage exhaust cam and throttles located in intake and exhaust manifold and Cold EGR passage. This system can be managed the mixing ratio of pre-mixture, hot internal EGR gas and cold external EGR gas. Indicated Mean Effective Pressure (IMEP) and 50% burnt fuel (CA50) are controlled by the mixing ratio. In this paper, steady combustion characteristics are examined to propose HCCI combustion control system. Moreover variation in HCCI combustion is discussed for load control.

An on-board measurement system that can simultaneously obtain such information as road infrastructure, traffic conditions, driver's operations, vehicle running conditions, and exhaust mass emissions was installed in a light duty freight vehicle with an EGR system and in a minivan without an EGR system. In order to analyze the mechanism of roadside pollution caused by vehicles, road tests were carried out in real traffic conditions. The light duty freight vehicle showed intensive NOx pollution at the roadside in a vehicle start, in which the EGR rate was low, but it was effective to reduce NOx mass emissions at low speed running in traffic jams where the EGR rate was rather high. In the case of the minivan, intensive NOx pollution was observed in low speed running such as in traffic jams. The reduction of NOx during vehicle starts is important for vehicles with an EGR system to reduce intensive NOx pollution at roadsides.

It has been investigated that thermal stratification and partial fuel stratification in a pre-mixture is effective as a method for controlling the combustion duration on HCCI combustion experiment. In this research, we analyze the effect of the degree of unmixedness in a pre-mixture on HCCI combustion characteristic using chemiluminescence imaging and thermodynamic analysis with RCM and Optical engine. In addition, numerical analysis was conducted on the gas compression and expansion strokes in HCCI engine with simple 0-dimensinal multi-zones model, and it was found that degree of unmixidness about temperature or partial fuel concentration plays a role for reducing pressure-rise rate.

The purpose of this study is to investigate experimentally the effect of partial mixing rate stratification on HCCI combustion, using DME and n-Butane. In addition to pressure measurement, the chemiluminescence image in HCCI combustion is used a means of visualizing a charge stratification and evaluating local combustion characters. It was found that partial mixing rate stratified charge in DME and n-Butane reduced the maximum pressure rise rate during HCCI combustion. By partial mixing rate stratified charge, the peak time of chemiluminescence intensity was dispersed, comparing to mixing rate homogeneous charge. Therefore, distribution of equivalence ratio is generated, and this distribution makes the peak time of RHR in each local area dispersed.

The purpose of this study is to investigate experimentally the effect of fuel stratification on HCCI combustion, using DME. In addition to pressure measurement, the chemiluminescence image in HCCI combustion is used a means of visualizing the charge stratification and evaluating local combustion characters. It was found that fuel stratified charge in DME reduced the maximum pressure rise rate during HCCI combustion. By fuel-stratified charge, the peak time of chemiluminescence intensity was dispersed, comparing to fuel homogeneous charge. Therefore, distribution of equivalence ratio is generated, and this distribution makes the peak time of RHR in each local area dispersed.

The Homogeneous Charge Compression Ignition (HCCI) engine is possible to achieve high thermal efficiency and low emissions. One of the main challenges with HCCI engines is structuring the systems to control combustion phasing, crank angle of 50% heat release (CA50), for keeping high thermal efficiency and avoiding an excessive rate of pressure rise which causes knocking, when operating conditions vary. Though some HCCI combustion control systems, for example Variable Valve Timing System and Variable Compression Ratio System, have been suggested, these control systems are complex and heavy.

(cont).... Due to the cycle-to-cycle variation, the change of total mass of fuel in cylinder has a big effect on IMEP. After misfire, unburned fuel and intermediates remain in exhaust gas, which is re-breathed as hot EGR gas, and unburned fuel and intermediates are supplied to next cycle. This leads to the total mass of fuel changes cycle-to-cycle. As a result of feedback control, transient performance is realized but high sensitivity of response cannot be achieved under the constant engine speed.

本研究はHCCI機関について，圧縮開始時質量平均ガス温度およびEGR率が燃焼位相に与える影響を調査した．HCCI機関に供給する３種のガス(空気と燃料の予混合気・高温EGRガス・低温EGRガス)の比率は，吸排気系に設けたスロットルバルブによって制御した．また，燃焼位相が過度に遅延したときに起きる燃焼変動のメカニズムの解析を行い，得られた知見をもとに燃焼変動低減のための制御アルゴリズムを構築しその性能の評価を行なった．