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The authors have reported significant smoke reduction in twin shaped semi-premixed diesel combustion with a newly designed combustion chamber to distribute the first and the second sprays into upper and lower layers. However, the first stage premixed combustion tends to advance far from the TDC, resulting in lowering of thermal efficiencies. In this report, improvement of thermal efficiency by optimizing the combustion phase with lower ignitability fuels was identified with the divided combustion chamber. The experiment was conducted with four fuels with different cetane numbers. The first stage premixed combustion can be retarded to the optimum phase with the fuel with cetane number 38, establishing high efficiencies.

In a natural gas fueled engine ignited by diesel fuel, the addition of hydrogen to the engine could be a possible way to improve thermal efficiency and reduce unburned methane which has a warming potential many times that of carbon dioxide as it promotes a more rapid and complete combustion. This study carried out engine experiments using a single cylinder engine with natural gas and hydrogen delivered separately into the intake pipe, and with pilot-injection of diesel fuel. The percentages of hydrogen in the natural gas-hydrogen mixtures were varied from 0% to 50% of the heat value. The results showed that the hydrogen addition has an insignificant effect on the ignition delay of the diesel fuel and that it shortens the combustion duration. The increase in the hydrogen ratio decreased the unburned hydrocarbon emissions more than the reduction of the amount of natural gas that was replaced by the hydrogen.

This paper presents a study on the effects of the engine size and rotation speed on diesel combustion characteristics and engine performance of two differently sized diesel engines (85 mm and 135 mm bores). For simplification of the evaluation, the experimental conditions were set based on the similarity rules proposed by Chikahisa. The combustion characteristics and the indicated thermal efficiencies were compared for the small and the large engines at the same engine speed. To examine the effects of the velocities of the in-cylinder gas and the fuel spray on the combustion and the thermal efficiency, the engine speed was changed in the small engine, while maintaining a non-dimensional engine speed.

To improve the combustion characteristics in semi-premixed diesel combustion, consisting in the first-stage premixed combustion of the primary fuel injection and the second-stage spray combustion of the secondary injection, the effect of splitting the primary injection was investigated in a diesel engine and analyzed with a CFD. The indicated thermal efficiency improves due to reductions in heat transfer losses to the in-cylinder wall and the combustion noise is suppressed with the split primary injections. The CFD analysis showed that the reduction in heat transfer loss with the split primary injections is due to a decrease in the combustion quantity near the combustion chamber wall.

A spark assist system was installed in a gasoline direct-injection single-cylinder test engine with the aim of controlling the ignition timing and accomplishing combustion of gasoline fuel by auto/compression ignition. A primary reference fuel having an octane number of 90 (PRF 90) was used to evaluate experimentally the spark assist function for gasoline auto/compression ignition and to examine the feasibility of combustion with a short ignition delay equivalent to conventional diesel combustion using the engine system. An optically accessible single-cylinder test engine was also used to evaluate and investigate spark-assisted auto/compression ignition. Ignition timing controllability with combinations of spark and injection timings for gasoline auto/compression ignition was also investigated under different operating load conditions.

Ammonia-selective catalytic reduction (SCR) systems have been introduced commercially in diesel vehicles, however catalyst systems with higher conversion efficiency and better control characteristics are required to know the actual emissions during operation and the emissions in random test cycles. Computational fluid dynamics (CFD) is an effective approach when applied to SCR catalyst development, and many models have been proposed, but these models need experimental verification and are limited in the situations they apply to. Further, taking account of redox cycle is important to have better accuracy in transient operation, however there are few models considering the cycle. Model development considering the redox reactions in a zeolite catalyst, Cu-ZSM-5, is the object of the research here, and the effects of exhaust gas composition on the SCR reaction and NH3 oxidation at high temperatures are investigated.

Nowadays, due to stringent emission regulations, it is imperative to incorporate modeling efforts with experiments. This paper presents the development of a phenomenological model to investigate the effects of various in-cylinder strategies on combustion and emission characteristics of a common-rail direct-injection (CRDI) diesel engine. Experiments were conducted on a single-cylinder, supercharged engine with displacement volume of 0.55 l at different operating conditions with various combinations of injection pressure, number of injections involving single injection and multiple injections with two injection pulses, and EGR. Data obtained from experiments was also used for model validation. The model incorporated detailed phenomenological aspects of spray growth, air entrainment, droplet evaporation, wall impingement, ignition delay, premixed and mixing-controlled combustion rates, and emissions of nitrogen oxides (NOx) and diesel soot.

Premixed diesel combustion is effective for high thermal efficiency and reductions of NOx and PM emissions, but a reduction of combustion noise is necessary for medium-high load engine operation. The control of the fuel injection has become more accurate because of the technical progress of the common rail fuel injection system, and the target heat release shape, calculated by computation, can be achieved by control of EGR, boosting, fuel injection timing, and injection quantity of multiple fuel injections. In this paper, the reduction of premixed diesel combustion noise maintaining high thermal efficiency has been investigated by the control of injection timings and heating values of multiple fuel injections. There are two aspects of the combustion noise reduction by multiple fuel injections. One is the reduction of the maximum rate of pressure rise in each combustion cycle, and the other is noise reduction effects by the noise cancelling spike (NCS) combustion.

Diesel particulate filters (DPF) are widely used in diesel engines, and forced regeneration is necessary to remove particulate matter (PM) accumulating on the DPF. This may be achieved with fuel injected after the main combustion is complete, the socalled “post fuel injection”, and supplied to the diesel oxidation catalyst (DOC) upstream of the DPF. This increases the exhaust gas temperature in the DOC and the DPF is regenerated with the high temperature gas flow. In most cases, the post fuel injection takes place at 30-90CA ATDC, and fuel may impinge on and adhere to the cylinder liner wall in some cases. Buddie and Pischinger [1] have reported a lubricant oil dilution with the post fuel injection by engine tests and simulations, and adhering fuel is a cause of worsening fuel consumption. In this paper, the impingement and adhesion of post diesel fuel injections on the cylinder liner was investigated by an optical method with a high pressure constant volume chamber (ϕ110mm, 883cm3).

The diesel spray characteristics in early pilot and late post fuel injections in a constant volume chamber which can create the in-cylinder conditions of a diesel engine were visualized with high speed video. At the early pilot and late post fuel injection, there was a longer penetration of the liquid phase fuel spray as well as slower evaporation. With normal heptane the impingement of liquid spray with early pilot and post fuel injections can be avoided due to a faster evaporation. The penetration of liquid phase fuel spray increases significantly at low IMEP and late post injection conditions with diesel fuel.

Diesel-like combustion of an emulsified blend of water and diesel fuel in a constant volume chamber vessel was visualized with high speed color video, further analyzing with a 2-D two color method and shadowgraph images. When the temperature at the fuel injection is 900 K, here while the combustion with unblended diesel fuel in the vessel is similar to ordinary diesel combustion with diffusive combustion, combustion with the emulsified fuel is similar to premixed diesel combustion with a large premixed combustion and very little diffusive combustion. With the emulsified fuel the flame luminosity and temperature are lower, the luminous flame and high temperature regions are smaller, and the duration of the luminous flame is shorter than with diesel fuel. This is due to promotion of premixing with increases in the ignition delay and decreases in the combustion temperature with the water vaporization.

To determine the engine noise reduction methods, an engine noise research was conducted experimentally with a PCCI diesel engine. The engine employed in the experiments was a supercharged, single-cylinder DI diesel engine with a high pressure common rail fuel injection system. The engine noise was sampled by two microphones and the sampled engine noise was averaged and analyzed by an FFT sound analyzer. The engine was equipped with a pressure transducer and the combustion noise was calculated from the power spectrum of the FFT analysis of the in-cylinder pressure wave form and the cross power spectrum of the sound pressure of the engine noise. It is well known that the maximum pressure rise rate is the main parameter related to the engine noise. The PCCI engine was operated at a 1.0 MPa/°CA maximum pressure rise rate to eliminate the effects of the maximum pressure rise rate, and parameters which had the dominant effect on engine noise and combustion noise were determined.

Characteristics of diesel combustion with low cetane number fuels with similar distillation temperatures to ordinary diesel fuel, including fuels with cetane number 32 and 39 (LC32, LC39), and a blend of n-cetane (n-hexadecane) and iso-cetane (2, 2, 4, 4, 6, 8, 8-heptamethylnonane) with cetane number 32 (CN32), were investigated. The effects of cooled exhaust gas recirculation (EGR) and pilot injection on characteristics of combustion and exhaust gas emissions with these fuels were examined in a naturally aspirated, single cylinder, diesel engine equipped with a common-rail fuel injection system. Even with the low cetane number fuels, quiet combustion with low levels of exhaust gas emissions comparable to ordinary diesel fuel was established by suitable control of intake oxygen levels and pilot injections.

The characteristics of smokeless low temperature diesel combustion in various fuel-air mixing was investigated by engine tests with high rates of cooled exhaust gas recirculation (EGR), three compression ratios, and fuels of various cetane numbers, as well as by computational fluid dynamics (CFD) simulation of the in-cylinder distributions of mixture concentration and temperature. The results show that besides combustion temperature, fuel-air mixing is also vital to efficient, smokeless, and low NOx diesel combustion. Smokeless and low NOx diesel combustion can be realized even with insufficient fuel-air mixing as long as the combustion temperature is sufficiently low. However low combustion temperature and insufficient oxygen due to ultra-high EGR cause very high UHC and CO emissions, and a severe deterioration in combustion efficiency.

Unregulated emissions from a DI diesel engine with ultra-high EGR low temperature combustion were analyzed using Fourier transform infrared (FTIR) spectroscopy and the reduction characteristics of both regulated and unregulated emissions by two exhaust catalysts were investigated. With ultra-high EGR suppressing the in-cylinder soot and Nox formation as well as with the exhaust catalysts removing the engine-out THC and CO emissions, clean diesel operation in terms of ultra-low regulated emissions (Nox, PM, THC, and CO) is established in an operating range up to 50% load. To realize smokeless low temperature combustion at higher loads, EGR has to be increased to a rate with the overall (average) excess air ratio less than the stoichiometric ratio.

The effects of blending ETBE to diesel fuel on the characteristics of low temperature diesel combustion and exhaust emissions were investigated in a naturally-aspirated DI diesel engine with large rates of cooled EGR. Low temperature smokeless diesel combustion in a wide EGR range was established with ETBE blended diesel fuel as mixture homogeneity is promoted with increased premixed duration due to decreases in ignitability as well as with improvement in fuel vaporization due to the lower boiling point of ETBE. Increasing the ETBE content in the fuel helps to suppress smoke emissions and maintain efficient smokeless operation when increasing EGR, however a too high ETBE content causes misfiring at larger rates of EGR. While the NOx emissions increase with increases in ETBE content at high intake oxygen concentrations, NOx almost completely disappears when reducing the intake oxygen content below 14 % with cooled EGR.

The effects of intake dilution with various dilution gases including nitrogen, argon, and carbon dioxide on low temperature diesel combustion were investigated in a naturally aspirated DI diesel engine to understand the mechanism of the simultaneous reductions in smoke and NOx with ultra-high EGR. NOx almost completely disappears with the intake oxygen concentration diluted below 16% regardless of the kind of dilution gas. Smoke emissions decrease with increased heat capacity of the charged gas due to promotion of mixture homogeneity with longer ignition delays. Intake dilution with the 36% CO2 + 64% Ar mixture which has a similar specific heat capacity as N2 shows lower smoke emissions than with N2. Chemical kinetics analysis shows that carbon dioxide may help to reduce NOx and soot by lowering the reaction temperature as well as by changing the concentrations of some radicals or/and species related to soot and NOx formation.

Palm oil has the important advantage of productivity compared to other vegetable oils such as rapeseed oil and soybean oil. However, the cold flow performance of palm oil methyl ester (PME) is poorer than other vegetable oil based biodiesel fuels. Previous research by the authors has shown that ethanol blending into PME improves the cold flow performance and considerably reduces smoke emission. The reduced smoke may be expected to allow an expansion in the EGR limit and lead to reduced NOx. This paper experimentally analyses the influence of EGR on smoke and NOx emissions from the diesel combustion with PME/ethanol blended fuel. The mechanisms in the smoke reduction are also analyzed.

This research investigates the influences of the injection timing, injection pressure, and compression ratio on the combustion and exhaust emissions in a single cylinder 1.0 L DI diesel engine operating with ultra-high EGR. Longer ignition delays due to either advancing or retarding the injection timing reduced the smoke emissions, but advancing the injection timing has the advantages of maintaining the thermal efficiency and preventing misfiring. Smokeless combustion is realized with an intake oxygen content of only 9-10% regardless of the injection pressure. Reduction in the compression ratio is effective to reduce the in-cylinder temperature and increase the ignition delay as well as to expand the smokeless combustion range in terms of EGR and IMEP. However, the thermal efficiency deteriorates with excessively low compression ratios.

The dependence of ultra-high EGR low temperature diesel combustion on fuel properties including cetane number and distillation temperature was investigated with a single-cylinder, naturally aspirated, 1.0 L, common rail DI diesel engine. Decreasing cetane number in fuels significantly reduces smoke emission due to an extension in ignition delay and the subsequent improvement in mixture formation. Smokeless combustion, ultra-low NOx, and efficient operating range with regard to EGR and IMEP are significantly extended by decreasing fuel cetane number. Changes in fuel distillation temperature do not result in significant differences in smoke emission and thermal efficiency for ultra-high EGR operation, and smokeless operation is established even with higher distillation temperature fuels as long as fuel cetane number is sufficiently low.