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The authors designed and produced a new dual fuel injector that allows two different kinds of fuel to be injected. This injector contains both a throttle type nozzle and a hole type which are located coaxially. The injection timing as well as the fuel quantity can be controlled individually. The running test using two lines of gas oil brought a good reduction of NOx and exhaust smoke. The experiment using gas oil and alcohol also brought a satisfactory reduction of exhaust emission.

Recently, dimethyl ether (DME) has been attracting much attention as a clean alternative fuel, since the thermal efficiency of DME powered diesel engine is comparable to diesel fuel operation and soot free combustion can be achieved. In this experiment, the effect of ambient pressure on DME spray was investigated with observation of droplet size such as Sauter mean diameter (SMD) by the shadowgraph and image processing method. The higher ambient pressure obstructs the growth of DME spray, therefore faster breakup was occurred, and liquid column was thicker with increasing the ambient pressure. Then engine performances and exhaust emissions characteristics of DME diesel engine were investigated with various compression ratios. The minimum compression ratio for the easy start and stable operation was obtained at compression ratio of about 12.

This work aimed to develop an LPG fueled direct injection SI engine, especially in order to improve the exhaust emission quality while maintaining high thermal efficiency comparable to a conventional engine. In-cylinder direct injection engines developed recently worldwide utilizes the stratified charge formation technique at low load, whereas at high load, a close-to-homogeneous charge is formed. Thus, compared to a conventional port injection engine, a significant improvement of fuel consumption and power can be achieved. To implement such a combustion strategy, the stratification of mixture charge is very important, and an understanding of its combustion process is also inevitably necessary. In this work, a numerical simulation was performed using a CFD code (KIVA-3), where the shape of a combustion chamber, swirl intensity, injection timing and duration, etc. were varied and their effects on the mixture formation and combustion process were investigated.

The oxidation mechanism of DTBP (Di-tertiary-butyl peroxide) and its role in butane oxidation have been investigated, as it pertains to the development of an LPG DI diesel engine. Ignition delay contours were analyzed to investigate the role of DTBP (ϕ≈0.2 to the total oxygen) in butane oxidation. At higher pressure and lower temperature regions, it was apparent that the addition of DTBP significantly enhances the ignition delay of butane, whereas at lower pressures and higher temperatures, this effect diminishes. Results of this study showed that the role of DTBP to enhance the ignition delay of the base fuel is through rapid heat release, rather than by radicals produced by decomposition during the base fuel ignition delay. Formaldehyde is a principal species involved in reactions for heat release in the higher pressure lower temperature region, comparable to diesel engine operating conditions.

To date, the DME combustion mechanism has been investigated by in-cylinder gas sampling, numerical calculations and observation of combustion radicals. It has been possible to quantify the emission intensities of in-cylinder combustion using a monochromator, and to observe the emitting species as images by using band-pass filters. However, the complete band images were not observed since the broadband (thermal) intensity may be stronger than band spectra intensities. Emission intensities of DME combustion radicals from a pre-mixed burner flame have been measured using a spectroscope and photomultiplier. Results were compared to other fuels, such as n-butane and methane, then, in this study, to better understand the combustion characteristics of DME, emission intensities near CH bands of an actual DI diesel engine fueled with DME were measured, and band spectra emitted from the engine were defined. Near TDC, emission intensities did not vary with wavelength.

Flame propagation characteristics, in a heavy-duty type LPG lean burn SI engine, were investigated by simulation methodology, using the global one step and the ten step chemical kinetic reaction mechanisms, respectively. The swirl ratio and equivalence ratio were varied to investigate their effects on flame front speed. The effect of increased swirl intensity on flame speed was very minor at ranges of equivalence ratio of this study. Flame front shape, however, was affected by swirl intensity. Circular flame front formed for a higher swirl ratio, which is in a qualitative accordance with that of measurements. Comparison between calculation and measurements of flame propagation characteristics shows a good agreement for both the global one step and the ten step chemical kinetic model. This work concludes that the reduced chemical kinetic reactions, consisting of ten steps, is useful for flame propagation study in an LPG SI engine.

Detailed chemical kinetic model of hydrogen peroxide (H2O2) into diesel exhaust gas has been executed to investigate its effect on the removal of nitric oxide(NO) by changing exhaust gas temperature and H2O2 addition amount. Flux analysis has also been done to clarify which reaction mainly affects NO-to-NO2 conversion. From the results of this study, it is shown that the optimal temperature condition to maximize the removal of NO exists near at 500K for OH addition condition, while that for H2O2 addition exists near at 800K. It is also shown that temperature window for the removal of NO becomes widened as the initial temperature of the exhaust gas increases, and NO-to-NO2 conversion rate decreases in proportion to the concentration of hydrocarbon(HC), although that of the total NOx remains the same level regardless of HC concentration. Finally, it is shown that HO2 + NO → NO2 + OH is mainly responsible for NO-to-NO2 conversion.

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%.

In order to reduce environmental disruption due to exhaust PM and NOx emissions from diesel engines of dimethyl ether (DME) has been proposed the use for the next generation vehicles, because the discharge of the atmospheric pollutants is less. In this study, DME is used to fuel a retrofit type diesel engine, and operational tests were carried out using a rotary distributor fuel injection pump. In this experiment, comparison and examination of the effects of fuel injection pressure, nozzle hole diameter, and injection timing. When using DME as an alternative fuel, the fuel temperature affects engine operation. And diameter of the injector nozzle hole and larger injection quantity is regarded as factors affecting the improvement in engine performance. In addition, for understanding the DME spray in the cylinder, DME was sprayed in a constant volume chamber where atmospheric temperature and pressure increased simultaneously, and the result is compared and examined with diesel fuel.

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.

Since dimethyl ether (DME) is a synthetic fuel, it is possible to make it from natural gas, coal and biomass. It is a low-emission, oxygenated fuel, which does not generate soot in the exhaust. Therefore, it has recently been identified as a possible replacement for diesel fuel. In Japan, the new short-term emissions regulations will be enforced beginning in 2003, and the long-term emissions regulations are scheduled to be enforced in 2005. In order to meet these more stringent emissions regulations, existing diesel engines would not be as widely used in the near future as they currently are. This will thus bring about a more widespread use of DME engines due to their low emissions potential. Moreover, when the modification of existing diesel engines into DME engines is available at a moderate cost, the wider use of DME engines can be expected. This study targeted development and application of DME engine technology for diesel engine retrofit, in a used diesel vehicle.

The mixture formation process in a premixed compression ignition engine was numerically analyzed. This study aimed to find out effective injection conditions for lean mixture formation with high homogeneity, since the NOx and soot emissions in the engine are closely related to the mixture homogeneity. To calculate fuel spray behavior, a practical computer code GTT (Generalized Tank and Tube) was employed. In a model for the premixed compression ignition engine, the effects of injection parameters, such as injection timing, initial droplet size, spray angle, injection velocity, nozzle type (pintle and hole) and injection position / direction, on the mixture homogeneity near ignition timing (or TDC) were investigated. To evaluate the homogeneity of the mixture, an index was defined based on the spatial distribution of fuel mass fraction. The fuel vapor mass fractions as well as the homogeneity indices, obtained as a function of time, were compared under various boundary conditions.

The engine performance and exhaust characteristics of the DME-powered diesel engine with an injection system developed for DME were investigated. The injection pump is an inline type that can inject double amount of DME fuel compared to the base injection pump because the calorific value of DME is about half lower than that of diesel fuel. The effect of injection timing on engine performances such as thermal efficiency, engine torque, and exhaust characteristics were investigated. Maximum torque and power with DME could be achieved the same or greater level compared to diesel fuel operation. Considering over all engine performances, the best dynamic injection timings without EGR were -3, -3, -6 and -9 deg. ATDC in 1120, 1680, 2240 and 2800 rpm engine speeds respectively in this experiment.

The performance of a medium duty DME truck was evaluated by field tests and engine bench tests. The DME vehicle was given a public license plate on October 2004, after which running tests were continued on public roads and a test course. The DME vehicle could run the whole distance, about 500 km, without refueling. The average diesel equivalent fuel consumption of the fully loaded DME truck was 5.75 km/l, running at 80 km/h on public highways. Remedying several malfunctions that occurred in the power-train subsystems enhanced the vehicle performance and operation. The DME vehicle accumulated 13,000 km as of August, 2006 with no observed durability trouble of the fuel injection pump. Disassembly and inspection of the fuel injectors after 7,700 km operation revealed a few differences in the nozzle tip and the needle compared to diesel fuel operation. However, the injectors were used again after cleanup.

In this study, a piezo disk was used to generate a cloud of n-decane fuel drops, which were mixed with air, then carried into a combustion chamber and ignited by a platinum wire. Microgravity data obtained at the Japan Microgravity Center (JAMIC) were compared to normal gravity data, all at 1Atm pressure and 20+/-1°C initial temperature. Under normal gravity the lean limit was found to be 7.6x106/mm3 (Φ = 1.0), and from this point the flame front speed steadily increased from 20cm/s up to a maximum flame front speed of 210cm/s at a fuel drop density of about 14x106/mm3 (Φ = 1.85). Microgravity data showed a much richer lean limit - about 14.5x106/mm3 (Φ = 1.9), and the flame front speed did not gradually rise to a peak value. Instead, the measurements indicated a peak value of about 250cm/s, with a steep increase followed by a gradual decrease at richer fuel air ratios. A cellular flame structure appeared, and the cell size decreased as the mixture density increased.

Flame propagation at elevated pressures for propane, butane and autogas (20% propane and 80% butane by mass) were investigated. Flame arrival time was measured using ionization probes installed along the wall of a cylindrical combustion chamber. Flame radius was also measured using a laser schlieren technique. Results showed that the flame front speed decreased with increasing initial pressure, and the initial pressure effect on maximum flame front speed was correlated by the relationship Sf = 175·pi-0.15 (for Φ=1.0). Characteristics of flame front speed between propane, butane and autogas were very similar, whereas at fuel-rich conditions flame front speed of butane and autogas were higher than that of propane. A thermodynamic model to predict flame radius and speed as a function of time was derived and tested using measured pressure-time curves.

DME as a fuel for compression ignition (diesel) engines has been actively studied for about ten years due to its characteristically low pollution and reputation as a “smokeless fuel”. During this time, the practical application is taking shape based on necessary tasks such as analysis of injection and combustion, engine performance, and development of experimental vehicles. At this moment, standardization of DME as a fuel was started under ISO in 2007. There are concerns regarding the impurities in DME regarding the mixing during production and distribution as well as their effect on additives for lubricity and odor. In this report, the effect of DME fuel impurities on performance of a DME powered diesel engine was investigated. The platform was a DME engine with common-rail fuel injection and was evaluated under partial load stable mode and Japanese transient mode (JE05) testing parameters.

The combustion mechanism of a fuel droplet cloud was studied by numerical simulation. We investigated how the flame front speed and combustion products changed depending on the equivalence ratio and initial temperature. Modeling was performed using the KIVA-III software package, a three dimensional analysis software used mainly for internal combustion engine applications. The computational domain was a horizontal 1x1x100 cell sector of a spherical combustion chamber and the fuel was n-decane. Results showed that when all the fuel droplets were assumed to have evaporated, the flame front speed increased from 28 cm/s to 152 cm/s as the equivalence ratio increased. The maximum flame front speed was reached at ϕ=1.1, beyond which it decreased (at richer overall equivalence ratios). With a constant equivalence ratio, the flame front speed decreased near the outside region, because the unburned gas was compressed by the expanding burned gas.

Dimethyl Ether (DME) is one of the major candidates for the next generation fuel for compression ignition (CI) engines. It has good self-ignitability and would not produce particulate, even at rich conditions. DME has proved to be able to apply to ordinary diesel engines with minimal modifications, but its combustion characteristics are not completely understood. In this study, the behavior of a DME spray and combustion process of a direct injection CI engine fueled with DME was investigated by combustion observation and in-cylinder gas sampling. To distinguish evaporated and non-evaporated zones of a spray, direct and schlieren imaging were carried out. The sampled gas from a DME spray was analyzed by gas chromatography, and the major intermediate product histories during ignition period were analyzed.

This is a preliminary work for the development of a stratified combustion engine using liquefied petroleum gas(LPG) as an alternative fuel. The main objective of this research is to find out the optimizing engine parameters from the viewpoint of mixture formation with the aid of simulation, where the KIVA_ code was used. The combustion characteristics of LPG and gasoline are different because of their different physical properties. Therefore, the numerical simulation was performed for optimizing engine parameters by changing the piston and cylinder geometry, as well as injection conditions. Result showed that geometry of combustion chamber has a great influence on mixture stratification. Also, weaker swirl seems to be better for mixture formation in the vicinity of the spark plug.