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The ignition delay under various temperature and pressure conditions considering volumetric change is investigated both by experiments and simulation to give some basic data of ignition delay for a DME DI diesel engine. The combustion process in a DME direct injected diesel engine was also observed to help understanding of the difference between DME combustion and that of a diesel fuel. For DME fuel, it was clear that the luminous flame duration is much shorter than that of diesel fuel. The calculated results of ignition delay for high equivalence(ϕ =0.4 in this study) showed good accord qualitatively to those of measured at wide range of temperature and pressure conditions investigated in this work. There exists the negative temperature coefficient region near the temperature of 800K. This study shows basic guideline for optimal injection timing for DME fueled compression ignition engines.

In this study, engine performances and exhaust emissions characteristics of compression ignition engine fueled with GTL were investigated by comparison with diesel fuel. Diesel engine could be operated fueled with GTL without any special modify for the test engine. With the high cetane number of GTL, the ignition lag was shorter, and the combustion started earlier than that of diesel fuel. Brake thermal efficiency operated with GTL increased at middle load conditions due to incomplete combustion emission such as CO and THC were lower than that of diesel fuel operation. NOx emission with GTL was comparable to diesel fuel, and there was a little decrease at high load. With GTL, soot emission was lower than with diesel fuel at above middle load condition. It seemed to be a reason of soot reduction that there was little sulphur contained in GTL.

In order to remove the diesel particulate matter (PM) and nitrogen oxides (NOx) from diesel exhaust, the gas is passed through a corona discharge collector for PM and another corona discharge device for NOx oxidation. With the PM collector, PM is accumulated on the central electrode, after that, it is removed by incineration technique. NOx concentration is decreased by oxidation to HNO3. In this study, these corona discharge reactors were coupled for removal of PM and NOx in progression, and attempted to remove these emissions in a slipstream of 14 liters/min of an experimental diesel engine and an actual vehicle, respectively. In case of the experimental test engine, it is found that nearly 100% and 15% of the PM and NOx emissions were removed even at a low input power of 26W (1560 J/L specific energy deposition). In the vehicle tests 1) a PM removal rate of 60% is obtained at an input power of over 40W, 2) a NOx removal rate of 97% is obtained at an input power of over 100W.

The tasks to improve diesel emissions and fuel consumption must be accomplished with urgency. However, due to the trade-off relationship between NOx emissions, soot emissions and fuel consumption, clean diesel combustion should be achieved by both innovative combustion and fuel technologies. The objective of this study is to extend the clean diesel combustion operating range (Engine-out emission: NOx ≺ 0.2 g/kWh, Soot ≺ 0.02 g/kWh). In this study, performance of a single-cylinder test engine equipped with a hydraulic valve actuation system and an ultra-high pressure fuel injection system was investigated. Also evaluated, were the effects of fuel properties such as auto-ignitability, volatility and aromatic hydrocarbon components, on combustion performance. The results show that applying a high EGR (Exhaust gas recirculation) rate can significantly reduce NOx emission with an increase in soot emission.

As an effective method to solve the global warming and the energy crisis, the research has been carried out for the adaptability of plant oil as an alternative fuel for Diesel engine. But there are the problems of engine performance and exhaust emissions owing to the high viscosity and low volatility, when the plant oil is used as a fuel. In order to eliminate these problems, spray characteristics of the DME (Dimethyl ether) blended plant oil has been examined by using the image processing based on the shadowgraph methodology. Results show that the optimum mixing ratio of the blend is about 50:50 (by weight %). Thereafter, experiments have been conducted with a DI Diesel engine using the DME blended plant oil, and compared the exhaust emissions with Diesel, DME and transesterified fuel operation. From the results, it can be concluded that the combustion characteristics of DME blended plant oil are comparable to Diesel fuel.

In this study, spray images of LPG Blended Fuels (LBF) for DI diesel engines were observed using a constant volume chamber at high ambient temperature and pressure, and the spray characteristics of the fuel were investigated. The LBF spray started to vaporize at the injector tip and the outer downstream regions of the spray, like diesel fuel, because of the high temperature at these areas. There were more vaporized areas compared to diesel fuel. Sufficient fuel injection volume and volatility of LBF resulted in good fuel-air mixture, then, THC emissions decreased compared to diesel fuel at high load engine test conditions. Butane spray image could not be observed at the injector tip. It seems that the high temperature of the injector tip caused the butane spray to vaporize rapidly. Spray tip penetration with LBF and butane were equal or greater than with diesel fuel. The high volatility of LBF and butane had no noticeable effect on spray penetration.

Spray characteristics of biodiesel oil was investigated as it can be applied to industrial combustion systems, including internal combustion engines. Shadowgraph methodology using Greenfield system was used to take some images of the spray and to measure droplet size. A high speed video camera was also used to take a picture of spray penetration and its angle. From the results, it shows that DME blended biodiesel oil has almost the same droplet size as conventional diesel oil, when the blended DME ratio is over 50% by weight. It is also shown that there exists optimum fuel injection pressure that has minimum droplet size when the ambient gas pressure is constant.

Band spectrum images for CH, OH and CHO were taken in a heavy duty type LPG lean-burn SI engine, to investigate the combustion process as it pertains to the pollutant formation process in the post flame region. Full spectra and band spectrum flame images were observed with a bottom view single cylinder research engine and two high speed cameras. NOx emissions were also measured for excess air ratios ranging from 1.0 to 1.6. A thermodynamic model, including the detailed chemical kinetic mechanism for LPG and NOx formation reactions, was developed to predict the major reaction species in the post flame region, and NOx emissions during the combustion process. The model qualitatively described the flame images for each band spectrum and could predict the measured NOx emissions very well.

For better understanding of the in-cylinder combustion characteristics of DME, combustion radicals of a direct injection DME-Fueled compression ignition engine were observed using a spectroscopic method. In this initial report, the emission intensity of OH, CH, CHO, C2 and NO radicals was measured using a photomultiplier. These radicals could be measured with wavelength resolution (half-width) as about 3.3 nm. OH and CHO radicals appeared first, and then CH radical emission was detected. After that, the combustion radicals were observed using a high-speed image intensified video camera with band-pass filter. All of radicals were able to observe as images with half-width as 6 or about 10 nm. Rich DME leaked from nozzle was burning at the end of combustion. Therefore, the second light emission of C2 radical after the main combustion was observed.

For better understanding of the combustion characteristics in a direct injection dimethyl ether (DME) engine, the chemiluminescences of a burner flame and in-cylinder flame were analyzed using the spectroscopic method. The emission intensities of chemiluminescences were measured by a photomultiplier after passing through a monochrome-spectrometer. For the burner flame, line spectra were found nearby the wave length of 310 nm, 430 nm and 515 nm, arising from OH, CH and C2 radicals, respectively. For the in-cylinder flame, a strong continuous spectrum was found from 340 nm wave length to 550 nm. Line spectra were also detected nearby 310 nm, 395 nm and 430 nm, arising from OH, HCHO, and C2 radicals, respectively, partially overlapping with the continuous spectrum. Of these line spectra, 310 nm of OH radical did not overlapped with the continuous spectrum.

To better understand the combustion characteristics of DME, emission intensities of DME combustion radicals from a pre-mixed burner flame were measured by a spectroscope and photomultiplier, Results were compared to other fuels, such as methane and butane. Large peaks in the band spectra from pre-mixed and diffusion DME flames were found near 310 nm, 430 nm, and 515 nm, arising from OH, CH and C2, respectively. The DME emission intensities decreased with increasing the equivalence ratio in this study. Notably, the relative decrease in the C2 band spectra peak was greater than that of the OH band. Comparing the pre-mixed DME and butane flames, the butane band spectra peaks were similar in shape, but much stronger than those for DME. However, it was remarkable that CH and C2 band spectra peaks decreased only slightly with increase in equivalence ratio compared to the DME case.

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.

Experiments were conducted to operate a direct injection (DI) diesel engine by using Liquefied Petroleum Gas (LPG) as a main fuel. Aliphatic Hydrocarbon (AH), cetane enhancing additive and lubricating additive were also added to the LPG so that smooth operation was achieved with a wide range of engine loads. Since the lubricity of LPG is lower than the diesel fuel therefore lubricating additive was employed to enhance the lubricity of LPG blended fuel. Furthermore, prototype LPG diesel truck was developed in this work, and the mileage reached about 70,000 km without any major failure. Prototype truck has good starting, good drive-off, acceleration and braking characteristics.

This research investigated the performance and emissions of a direct injection (DI) Diesel engine operated on 100% butane liquid petroleum gas (LPG). The LPG has a low cetane number, therefore di-tertiary-butyl peroxide (DTBP) and aliphatic hydrocarbon (AHC) were added to the LPG (100% butane) to enhance cetane number. With the cetane improver, stable Diesel engine operation over a wide range of the engine loads was possible. By changing the concentration of DTBP and AHC several different LPG blended fuels were obtained. In-cylinder visualization was also used in this research to check the combustion behavior. LPG and only AHC blended fuel showed NOX emission increased compared to Diesel fuel operation. Experimental result showed that the thermal efficiency of LPG powered Diesel engine was comparable to Diesel fuel operation. Exhaust emissions measurements showed that NOX and smoke could be considerably reduced with the blend of LPG, DTBP and AHC.

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.

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.

In this research, a test apparatus (VPT-HFRR) for evaluating lubricity was manufactured at an arbitrary pressure according to the lubricity test method (HFRR) for diesel fuel. The lubricity of LPG blended fuel (LBF) for diesel engines was examined using VPT-HFRR., This was a value close to that of diesel fuel, and when a suitable lubricity had been maintained, it was checked. Prototype trucks were manufactured and their durability was examined. After a run of 70,000km or more, no serious trouble had occurred, and when LBF was maintained at a suitable lubricity, it was checked.

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.

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.

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.