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The objective of the present research is to investigate the effects on diesel engine combustion and NOx and PM emission characteristics in case of blending the ordinary diesel fuel with biodiesel in passenger car diesel engines. Firstly, we conducted experiments to identify the combustion and emissions characteristics in a modern diesel engine complying with the EURO 4 emission standard. Then, we developed a numerical simulation model to explain and generalize biodiesel combustion phenomena in detail and generalize emission characteristics. The experimental and simulation results are useful to reduce biodiesel emissions by controlling engine operating and design parameters in the diesel engine. Engine tests were conducted and a mathematical model created to investigate the effects of 40% and 100% methyl oleate modeled fuel representing Jatropha-derived biodiesel on diesel combustion and emission characteristics, over a wide range of passenger car DI diesel engine operating conditions.

To improve urban air pollution, stringent emissions regulations for heavy-duty diesel engines have been proposed and will become effective in Japan, the EU, and the United States in a few years. To comply with such future regulations, it is critical to investigate the effects of intake and injection parameters and fuel properties on engine performance, efficiency and emissions characteristics, associated with the use of aftertreatment systems. An experimental study was carried out to identify such effects. In addition, the KIVA-3 code was used to gain insight into cylinder events. The results showed improvements in NOx-Smoke and BSFC trade-offs at high-pressure injection in conjunction with EGR and supercharging.

To suppress knock in small gasoline engines, the coolant flow of a single-cylinder engine was improved by using two methods: a multi-dimensional knock prediction method combining a Flamelet model with a simple chemical kinetics model, and a method for predicting combustion chamber wall temperature based on a thermal fluid calculation that coupled the engine coolant and the engine structure (engine head, cylinder block, and head gasket). Through these calculations as well as the measurement of wall temperatures and the analysis of combustion by experiments, the effects of wall temperature distribution and consequent unburnt gas temperature distribution on knock onset timing and location were examined. Furthermore, a study was made to develop a method for cooling the head side, which was more effective to suppress knock: the head gasket shape was modified to change the coolant flow and thereby improve the distribution of wall temperatures on the head side.

An experimental and numerical study has been conducted on the emission and reduction of HCHO (formaldehyde) and other pollutants formed in the cylinder of a direct-injection diesel engine fueled by methanol. Engine tests were performed under a variety of intake conditions including throttling, heating, and EGR (exhaust gas recirculation) for the purpose of improving these emissions by changing gas compositions and combustion temperatures in the cylinder. Moreover, a detailed kinetics model was developed and applied to methanol combustion to investigate HCHO formation and the reduction mechanism influenced by associated elementary reactions and in-cylinder mixing.

A numerical model has been developed to predict the formation of NOx and formaldehyde in the combustion and post-combustion zones of a methanol DI engine. For this purpose, a methanol-air mixture model combined with a full kinetics model has been introduced, taking into account 39 species with their 157 related elementary reactions. Through these kinetic simulations, a concept is proposed for optimizing methanol combustion and reducing exhaust emissions.

A numerical study was carried out to investigate auto-ignition characteristics during HCCI predicted by using zero and multi-dimensional models combined with detailed kinetics including 116 chemical species and 689 elementary reactions involving iso-octane. In the simulation, homogeneous charge compression ignition of the fuel was analyzed under the same conditions as encountered in internal combustion engines. The results elucidated the combustible region and oxidation process of iso-octane with the formation and destruction of various chemical species in the cylinder.

To facilitate research and development of diesel engines, the universal numerical code for predicting diesel combustion has been favored for the past decade. In this paper, the finite-rate elementary chemical reactions, sometimes called the detailed chemical reactions, are introduced into the KIVA-3V code through the use of the Partially Stirred Reactor (PaSR) model with the KH-RT break-up, modified collision and velocity interpolation models. Outcomes were such that the predicted pressure histories have favorable agreements with the measurements of single and double injection cases in the diesel engine for use in passenger cars. Thus, it is demonstrated that the present model will be a useful tool for predicting ignition and combustion characteristics encountered in the cylinder.

Natural gas is a promising alternative fuel for internal combustion engines because of its clean combustion characteristics and abundant reserves. However, it has several disadvantages due to its low energy density and low thermal efficiency at low loads. Thus, to assist efforts to improve the thermal efficiency of spark-ignited (SI) engines operating on natural gas and to minimize test procedures, a numerical simulation model was developed to predict and optimize the performance of a turbocharged test engine, considering flame propagation, occurrence of knock and ignition timing. The numerical results correlate well with empirical data, and show that increasing compression ratios and retarding the intake valve closing (IVC) timing relative to selected baseline conditions could effectively improve thermal efficiency. In addition, employing moderate EGR ratios is also effective for avoiding knock.

It has been recognized that alternative fuels such as liquid petroleum gas (LPG) has less polluting combustion characteristics than diesel fuel. Direct-injection stratified-charge combustion LPG engines with spark-ignition can potentially replace conventional diesel engines by achieving a more efficient combustion with less pollution. However, there are many unknowns regarding LPG spray mixture formation and combustion in the engine cylinder thus making the development of high-efficiency LPG engines difficult. In this study, LPG was injected into a high pressure and temperature atmosphere inside a constant volume chamber to reproduce the stratification processes in the engine cylinder. The spray was made to hit an impingement wall with a similar profile as a piston bowl. Spray images were taken using the Schlieren and laser induced fluorescence (LIF) method to analyze spray penetration and evaporation characteristics.

From the viewpoint of utilizing methanol fuel in an automotive turbocharged direct-injection diesel engine, an intercooling system supplying liquid methanol has been devised and its effects on engine performance and exhaust gas emissions have been investigated. With an electronically controlled injector in this system, methanol as a supplementary fuel to diesel fuel can be injected into the intake pipe in order to intercool a hot air charge compressed by the turbocharger. It has been confirmed that especially at heavy load conditions, methanol-intercooling can yield a higher thermal efficiency, and lower NOx and smoke emissions simultaneously, compared with three other cases without using methanol: natural aspiration and the cases with and without an ordinary intercooler. However, methanol fueling must be avoided at lower loads since sacrifices in efficiency and hydrocarbon emissions are inevitably involved.

A dual fuel natural gas diesel engine suffers from remarkably lower thermal efficiency and higher THC, CO emissions at lower load because of its lower burned mass fraction caused by the lean pre-mixture. To overcome this inevitable disadvantage at lower load, two methods of reducing the number of operating cylinders were examined. One method was to use the two cylinders operation while the second one was to use the quasi-two cylinders operation. As a result, it was found that the unburned hydrocarbons and CO emissions could be favorably reduced with the improvement of thermal efficiency by reducing the number of cylinders to half for a dual fuel natural gas diesel engine. Moreover, it was also found that the quasi-two cylinders operation could improve the torque fluctuation more compared to the two cylinders operation.

In this study, we selected four unregulated emissions species, formaldehyde, benzene, 1,3-butadiene and benzo[a]pyrene to research the emission characteristics of these unregulated components experimentally. The engine used was a water-cooled, 8-liter, 6-cylinder, 4-stroke-cycle, turbocharged DI diesel engine with a common rail fuel injection system manufactured for the use of medium-duty trucks, and the fuel used was JIS second-class light gas oil, which is commercially available as diesel fuel. The results of experiments indicate as follows: formaldehyde tends to be emitted under the low load condition, while 1,3-butadiene is emitted at the low engine speed. This is believed to be because 1,3-butadiene decomposes in a short time, and the exhaust gas stays much longer in a cylinder under the low speed condition than under the high engine speed one. Benzene is emitted under the low load condition, as it is easily oxidized in high temperature.

A study has been made of an automotive direct-injection diesel engine in order to identify the effects of the combustion chamber geometry on combustion, with special emphasis focused on a re-entrant combustion chamber. Conventional combustion chambers and a re-entrant one were compared in terms of the combustion process, engine performance and NOx and smoke emissions. Heat transfer calculations and heat release analyses show that the re-entrant chamber tends to reduce ignition lag due to the higher temperatures of the wall on which injected fuel impinges. Analyses of turbulent flow characteristics in each chamber indicate that the re-entrant chamber enhances combustion because of the higher in-cylinder velocity accompanied by increased turbulence. Further, analyses of in-cylinder gas samples show lower soot levels in the re-entrant chamber. As a result, a good compromise can be achieved between fuel economy and exhaust emissions by retarding the fuel injection timing.

This study examines the effects of ethanol content on engine performances and the knock characteristics in spark ignition gasoline engine under various compression ratio conditions by cylinder pressure analysis, visualization and numerical simulation. The results confirm that increasing the ethanol content provides for greater engine torque and thermal efficiency as a result of the improvement of knock tolerance. It was also confirmed that increasing the compression ratio together with increasing ethanol content is effective to overcome the shortcomings of poor fuel economy caused by the low calorific value of ethanol. Further, the results of one dimensional flame propagation simulation show that ethanol content increase laminar burning velocity. Moreover, the results of visualization by using a bore scope demonstrate that ethanol affects the increase of initial flame propagation speed and thus helps suppress knock.

A mixed time-scale subgrid large eddy simulation was used to simulate mixture formation, combustion and soot formation under the influence of turbulence during diesel engine combustion. To account for the effects of engine wall heat transfer on combustion, the KIVA code's standard wall model was replaced to accommodate more realistic boundary conditions. This were carried out by implementing the non-isothermal wall model of Angelberger et al. with modifications and incorporating the log law from Pope's method to account for the wall surface roughness. Soot and NOx emissions predicted with the new model are compared to experimental data acquired under various EGR conditions.

A new type of fuel injection nozzle, called a “slit nozzle,” has been developed to improve poor ignitability and to stabilize combustion under low load conditions in direct-injection methanol diesel engines manufactured for medium-duty trucks. This nozzle has a single oblong vent like a slit. Engine test results indicate that the slit nozzle can improve combustion and thermal efficiency, especially at low loads and no load. This can be explained by the fact that the slit nozzle forms a more highly concentrated methanol spray around the glow-plug than do multi-hole nozzles. As a result, this nozzle improves flame propagation.

Dual-fuel operation of a direct-injection diesel engine with natural gas fuel can yield a high thermal efficiency almost comparable to the diesel operation at higher loads. The dual-fuel operation, however, at lower loads inevitably suffers from lower thermal efficiency and higher unburned fuel. To improve this problem, engine tests were carried out on a variety of engine parameters including diesel fuel injection timing advance, intake throttling and hot and cooled exhaust gas recirculation (EGR). It was found that diesel injection timing advance gave little improvement in thermal efficiency and increased NOx. Intake throttling promoted better combustion and shortened its duration with a consequent improvement in efficiency at higher natural gas fractions. Hot EGR raised thermal efficiency, reduced smoke levels, and maintained low NOx levels. Cooled EGR reduced NOx emissions but lowered thermal efficiency.

With the development of downsized spark ignition (SI) engines, low-speed pre-ignition (LSPI) has been observed more frequently as an abnormal combustion phenomenon, and there is a critical need to solve this issue. It has been acknowledged that LSPI is not directly triggered by autoignition of the fuel, but by some other material with a short ignition delay time. It was previously reported that LSPI can be caused by droplets of lubricant oil intermixed with the fuel. In this work, the ignition behavior of lubricant component containing fuel droplets was experimentally investigated by using a constant volume chamber (CVC) and a rapid compression and expansion machine (RCEM), which enable visualization of the combustion process in the cylinder. Various combinations of fuel compositions for the ambient fuel-air mixture and fractions of base oil/metallic additives/fuel for droplets were tested.

Natural gas is an attractive alternative fuel for internal combustion engines. Homogeneous charge compression ignition (HCCI) combustion is considered to be one of the most promising measures for increasing thermal efficiency and reducing emissions, but it is difficult to control and stabilize its ignition and combustion processes. This paper describes an experimental study of natural gas combustion utilizing two types of ignition assistance. Spark assistance, which is used for conventional spark ignition (SI) engines, and pilot diesel injection, hereinafter called diesel pilot, which generates multiple ignition points by using a small injection of diesel that accounts for 2% of the total heat release for the cycle. The performance of these two approaches was compared with respect to various combustion characteristics when burning homogeneous natural gas mixtures at a high compression ratio.

The objective of the present research was to analyze the effects of using oxygenated fuels (FAMEs or biodiesel fuels) on injected fuel spray and soot formation. A 3-D numerical study which using the KIVA-3V code with modified chemical and physical models was conducted. The large-eddy simulation (LES) model and KH-RT model were used to simulate fuel spray characteristics. To predict soot formation processes, a model for predicting gas-phase polycyclic aromatic hydrocarbons (PAHs) precursor formation was coupled with a detailed phenomenological particle formation model that included soot nucleation from the precursors, surface growth/oxidation and particle coagulation. The calculated liquid spray penetration results for all fuels agreed well with the measured data. The spray measurements were conducted using a constant volume chamber (CVC), which can simulate the ambient temperature and density under real engine conditions.