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Bio-ethanol is one of the candidates for automotive alternative fuels. For reduction of carbon dioxide emissions, it is important to investigate its optimum combustion procedure. This study has explored effect of ethanol fuels on HCCI-SI hybrid combustion using dual fuel injection (DFI). Steady and transient characteristics of the HCCI-SI hybrid combustion were evaluated using a single cylinder engine and a four-cylinder engine equipped with two port injectors and a direct injector. The experimental results indicated that DFI has the potential for optimizing ignition timing of HCCI combustion and for suppressing knock in SI combustion under fixed compression ratio. The HCCI-SI hybrid combustion using DFI achieved increasing efficiency compared to conventional SI combustion.

Recently natural gas has attracted public attention as clean fuel for motor vehicles. We first developed a heavy-duty compressed natural gas (CNG) engine for city busses and manufactured many CNG-fueled engines. Both medium- and heavy-duty CNG engines achieved very low exhaust emissions. However, the fuel consumption of these engines for example the city-bus application are higher than that of a diesel engine. For this reason, these CNG engines always operate under the part-load conditions. Therefore, we developed a direct-injected CNG engine. Under a part-load condition, the engine is operated on the stratified-charged natural gas that is directly injected into the combustion chamber. It is the most important that the air/fuel ratio of the mixture stratified near the spark plug must be controlled to achieve the stable mixture condition.

In this study, performance and emissions characteristics of an LPG direct injection (DI) engine with a rotary distributor pump were examined by using cetane enhanced LPG fuel developed for diesel engines. Results showed that stable engine operation was possible for a wide range of engine loads. Also, engine output power with cetane enhanced LPG was comparable to diesel fuel operation. Exhaust emissions measurements showed NOx and smoke could be reduced with the cetane enhanced LPG fuel. Experimental model vehicle with an in-line plunger pump has received its license plate in June 2000 and started high-speed tests on a test course. It has already been operated more than 15,000 km without any major failure. Another, experimental model vehicle with a rotary distributor pump was developed and received its license plate to operate on public roads.

The objective of this study is to clarify the effects of fuel properties on the stratified-charge combustion of direct-injection gasoline engine with EGR. A single-cylinder direct-injection gasoline engine, based on a Toyota D-4 engine, was used. First, the effects of EGR on the stratified-charge combustion of direct-injection gasoline engine were investigated under various conditions. As a result, 20% EGR can drastically reduce NOx emission without reducing the IMEP under the stratified-charge combustion. Next, paraffin, olefin, naphthene and ether having a boiling point of approximately 50 °C and paraffin, olefin and aromatic compounds having a boiling point of approximately 100°C were used for fuel to investigate the effects of fuel properties on the stratified-charge combustion of a direct-injection gasoline engine with EGR. As a result, the effects of fuel properties on the stratified-charge combustion of direct-injection gasoline engine were maintained by the use of EGR.

Several types of oxidation catalyst material are tested in repeated particulate emission measurements over the US HDD transient test procedure. Particulates are effectively reduced in the initial stage of the measurements. However, particulates tend to increase when repeating the measurements. This is believed to be caused by sulfate adsorption on the catalyst surfaces. Hence, oxidation catalysts are tested after stabilizing surface adsorption. Test results show that an oxidation catalyst which forms more sulfates is not effective in reducing particulates because the sulfate increase offsets the SOF reduction effect. An effective catalyst for particulate reduction is developed by suppressing sulfate formation.

Compression ignition combustion with a lean mixture has high potential in terms of high theoretical thermal efficiency and low NOx emission characteristics due to low combustion temperatures. In particular, a Dual-Fuel concept is proposed to achieve high ignition timing controllability and an extended operation range. This concept controls ignition timing by adjusting the fraction of two fuels with different ignition characteristics. However, a rapid combustion process after initial ignition cannot be avoided due to the homogenous nature of the fuel mixture, because the combustion process depends entirely on the high reaction rate of thermal ignition. In this study, the effect of mixture stratification in the cylinder on the combustion process after ignition based on the Dual-Fuel concept was investigated. Port injection of one fuel creates the homogeneous mixture, while direct injection of the other fuel prepares a stratified mixture in the cylinder at the compression stroke.

In practical lean burn engines used to date, the use of a stratified air-fuel configuration, with a comparatively rich mixture in the vicinity of the spark plugs, has resulted in the stable combustion of an overall lean mixture. However, because a comparatively rich mixture is burned during the first half of combustion, NOx emissions are not reduced sufficiently. This research focused on a form of lean burn with homogeneous premixture that would be able to balance low NOx emissions with combustion controllability. It is widely known that homogeneous lean premixed gas has poor flame propagation characteristics. To determine the dominant cause of this, this study investigated the combustion properties of a single-cylinder engine while changing the compression ratio and intake temperature. As a result, the primary cause of combustion fluctuation, the abnormal cycle has a low TDC temperature compared to that of other cycles.

Experiments using a single-cylinder direct-injection gasoline engine were conducted to evaluate pure substances and refinery feedstocks in order to clarify the effects of fuel properties on the combustion and emission of the direct-injection gasoline engine. Under the stratified charge combustion conditions, olefins had shorter mass-burning periods with a higher indicated mean effective pressure (IMEP), lower hydrocarbon (HC) emissions and higher NOx emissions than other substances. The boiling point affected the mass-burning periods and the HC emissions of paraffins. Aromatic compounds caused poor combustion and smoke production. Under the homogeneous stoichiometric combustion conditions, the combustion of substances was affected by both their boiling points and their chemical properties. Also, a shorter mass-burning period induced a higher IMEP and a lower coefficient of variance of the IMEP.

A feasibility study of an LPG DI diesel engine has been carried out to study the effectiveness of two selected cetane enhancing additives: Di-tertiary-butyl peroxide (DTBP) and 2-Ethylhexyl nitrate (EHN). When more than either 5 wt% DTBP or 3.5 wt% 2EHN was added to the base fuel (100 % butane), stable engine operation over a wide range of engine loads was possible (BMEPs of 0.03 to 0.60 MPa). The thermal efficiency of LPG fueled operation was found to be comparable to diesel fuel operation at DTBP levels over 5 wt%. Exhaust emissions measurements showed that NOx and smoke levels can be significantly reduced using the LPG+DTBP fuel blend compared to a light diesel fuel at the same experimental conditions. Correlations were derived for the measured ignition delay, BMEP, and either DTBP concentration or cetane number. When propane was added to a butane base fuel, the ignition delay became longer.

Performance and emissions of an LPG lean burn engine for heavy duty vehicles were measured. The piston cavity, swirl ratio, propane - butane fuel ratio, and EGR were varied to investigate their effects on combustion, and thus engine performance. Three piston cavities were tested: a circular flat-bottomed cavity with sloped walls (called the “bathtub” cavity), a round bottomed cavity (called the “dog dish” cavity), and a special high-turbulence cavity (called the “nebula” cavity). Compared to the bathtub and dog dish cavities, the nebula type cavity showed the best performance in terms of cyclic variation and combustion duration. It was capable of maintaining leaner combustion, thus resulting in the lowest NOx emissions. High swirl improved combustion by achieving a high thermal efficiency and low NOx emissions. In general, as the propane composition increased, cyclic variation fell, NOx emissions increased, and thermal efficiency was improved.

Using an extended bottom view piston having a quartz window, flame propagation observation and flame contour analysis were carried out to investigate the combustion characteristics of a heavy-duty type LPG lean burn engine. The swirl ratio and piston cavity configuration were varied to investigate their effects on combustion and engine performance. Gradual reduction of NOx but increased hydrocarbon emissions were measured for leaner mixtures compared to the stoichiometric operation. High swirl apparently accelerated the initial flame kernel development, as evidenced by a shorter crank angle interval from the spark ignition to the maximum cylinder pressure. The ‘D’ type cavity, with an increased squish area located below the intake valve, was shown to have the shortest burn duration among the piston cavities tested. The experimental flame propagation observation procedure was shown to be useful for the study of the combustion process in engines.

Development of LPG SI and CI engines for heavy duty vehicles has been carried out. In order to measure the performance and emissions of an LPG lean burn SI engine, the piston cavity, swirl ratio, and propane-butane fuel ratio were varied and tested. Compared to the bathtub and dog dish cavities, the nebula type cavity showed the best performance in terms of cyclic variation and combustion duration. High swirl improved combustion by achieving a high thermal efficiency and low NOx emissions. A feasibility study of an LPG DI diesel engine also has been carried out to study the effectiveness of the selected cetane enhancing additives:Di-tertiary-butyl peroxide (DTBP). When more than 5 wt% DTBP was added to the base fuel, stable engine operation over a wide range of engine loads was possible. The thermal efficiency of LPG fueled operation was found to be comparable to diesel fuel operation at DTBP levels over 5 wt%.