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The objective of this paper is to investigate the potential of lean burn combustion to improve the thermal efficiency of spark ignition engine. Experiments used a single cylinder gasoline spark ignition engine fueled with primary reference fuel of octane number 90, running at 4000 revolution per minute and at wide open throttle. Experiments were conducted at constant fueling rate and in order to lean the mixture, more air is introduced by boosted pressure from stoichiometric mixture to lean limit while maintaining the high output engine torque as possible. Experimental results show that the highest thermal efficiency is obtained at excess air ratio of 1.3 combined with absolute boosted pressure of 117 kPa. Three dimensional computational fluid dynamic simulation with detailed chemical reactions was conducted and compared with results obtained from experiments as based points.

The objective of the present research is to analyze the effects of using oxygenated fuels (FAMEs) on diesel engine combustion and emission (NOx and soot). We studied methyl oleate (MO), which is an oxygenated fuel representative of major constituents of many types of biodiesels. Engine tests and numerical simulations were performed for 100% MO (MO100), 40% MO blended with JIS#2 diesel (MO40) and JIS#2 diesel (D100). The effects of MO on diesel combustion and emission characteristics were studied under engine operating conditions typically encountered in passenger car diesel engines, focusing on important parameters such as pilot injection, injection pressure and exhaust gas recirculation (EGR) rate. We used a diesel engine complying with the EURO4 emissions regulation, having a displacement of 2.2 L for passenger car applications. In engine tests comparing MO with diesel fuel, no effect on engine combustion pressure was observed for all conditions 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 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.

We have constructed a quasi-2-dimensional NH₃-SCR model with detailed surface reactions to analyze the NOx conversion mechanism and reasons for its inhibition at low temperatures. The model consists of seven detailed surface reactions proposed by Grozzale et al., and calculates longitudinal gas flow, gas phase-catalyst phase mass transfer, and mass diffusion within the catalyst phase in the depth dimension. Using the model, we have analyzed the results of pulsed ammonia (NH₃) feed tests at various catalyst temperatures, and results show that ammonium nitrate (NH₄NO₃) is the inhibitor in NH₃-SCR reactions at low temperatures. In addition, we found that cutting the supply of NH₃ causes decomposition of NH₄NO₃, providing surface ammonia (NH₄+), which rapidly reacts with adjacent NOx, leading to an instantaneous rise in nitrogen (N₂) formation.

Model based control design is an important method for optimizing engine operating conditions so as to simultaneously improve engines' thermal efficiency and emission profiles. Modeling of intake system that includes an intake throttle valve, an EGR valve and a variable geometry turbocharger was constructed based on conservation laws combined with maps. Calculated results were examined the predictive accuracy of fresh charge mass flow, EGR rate and boost pressure.

This paper describes the development of a High Speed Calculation Diesel Combustion Model that predicts combustion-related behaviors of diesel engines from passenger cars. Its output is dependent on the engine's operating parameters and on input from on-board pressure and temperature sensors. The model was found to be capable of predicting the engine's in-cylinder pressure, rate of heat release, and NOx emissions with a high degree of accuracy under a wide range of operating conditions at a reasonable computational cost. The construction of this model represents an important preliminary step towards the development of an integrated Model Based Control system for controlling combustion in diesel engines used in passenger cars.

The efficiency of the NOx Storage and Reduction (NSR) catalysts used in the aftertreatment of diesel engine exhaust gases can potentially be increased by using reactive reductants such as CO and H₂ that are formed during in-cylinder combustion. In this study, a multi-dimensional computational fluid dynamics (CFD) code coupled with complex chemical analysis was used to study combustion with various fuel after-injection patterns. The results obtained will be useful in designing fuel injection strategies for the efficient formation of CO.

Compared with petroleum fuel, liquefied petroleum gas (LPG) demonstrates advantages in low CO₂ emission. This is because of propane (C₃H₈), n-butane (n-C₄H₁₀) and i-butane (i-C₄H₁₀), which are the main components of LPG, making H/C ratio higher. In addition, LPG is suitable for high efficient operation of a spark ignition (SI) engine due to its higher research octane number (RON). Because of these advantages, that is, diversity of energy source and reduction of CO₂, in the past several years, LPG vehicles have widely been used as the alternate gasoline vehicles all over the world. Consequently, it is absolutely essential for the performance increase in LPG vehicles to comprehend combustion characteristics of LPG. In this study, the differences of laminar burning velocity between C₃H₈, n-C4H10, i-C₄H₁₀ and regular gasoline were evaluated experimentally with the use of a constant volume combustion chamber (CVCC).

Difference of engine combustion characteristics, species and amount of exhaust gas and PM (particulate matter consisted of SOF and Soot and Ash), and especially PM oxidation characteristics were studied when diesel fuel or bio-fuel, here PME (palm oil methyl ester) as an example, was used as a fuel. The fueling rate was adjusted to obtain the same torque for both fuels and engine was operated under several range of EGR (Exhaust Gas Recirculation) ratio. Under such conditions, PME showed shorter ignition delay time and lower R.H.R (rate of heat release) under 0-40% EGR ratio. With respect to engine exhaust gas species, CO, NO, THC and HCHO, CH3CHO concentration was almost the same when the EGR ratio is higher than 35% (Intake-Air/Fuel: A/F=20). However, PME also showed lower exhaust gas emission when the EGR ratio is higher than 30%.

In this study, fuel ignition timing parameters, in-cylinder pressure and heat release rates, and quantities of major exhaust gas emissions from a diesel engine were calculated using multi-dimensional CFD codes coupled with complex chemistry analysis. In addition, a sensitivity analysis of parameters was conducted to identify the major variables affecting these diesel combustion parameters. Firstly, diesel combustion analysis under typical operating conditions was carried out to validate the analytical methods used in the study, and then the effects of intake gas variables (e.g. temperature, and pressure) were investigated in detail in the sensitivity analysis. The results show that the main determinant of ignition timing in the engine is the spatial density of oxygen in the cylinder. This finding indicates that diesel combustion with high EGR and high boost pressure can provide both high thermal efficiency and low emissions.

The aim of this study is to demonstrate the concept of gasoline lift-off spray combustion in which the burning velocity is controlled by the rate of mixture supply to the flame zone. With this concept, gasoline fuel is injected under high pressure to promote atomization, evaporation and mixing with the air, thereby quickly forming a homogenous mixture extending to the flame downstream of the spray. As a result, the injected fuel is burned sequentially. In this study, a constant-volume combustion vessel was used to visualize and analyze spray combustion. The experimental results made clear the effects of the initial conditions (e.g., injection pressure and nozzle hole diameter) and the ambient conditions (e.g., temperature and pressure) on the flame lift-off length and soot formation. In addition, the conditions facilitating this combustion concept were examined by conducting combustion simulations with the KIVA-3V code, taking into account the detailed chemical reaction mechanisms.

A variable valve timing (VVT) mechanism has been applied in a high-speed direct injection (HSDI) diesel engine. The effective compression ratio (εeff) was lowered by means of late intake valve closing (LIVC), while keeping the expansion ratio constant. Premixed charge compression ignition (PCCI) combustion, adopting the Miller-cycle, was experimentally realized and numerically analyzed. Significant improvements of NOx and soot emissions were achieved for a wide range of engine speeds and loads, frequently used in a transient mode test. The operating range of the Miller-PCCI combustion has been expanded up to an IMEP of 1.30 MPa.

In a Diesel Oxidation Catalyst (DOC) and Catalyzed Soot Filter (CSF) system, the DOC is used to oxidize additional fuel injected into the cylinder and/or exhaust pipe in order to increase the CSF's inlet temperature during soot regeneration. The catalyst's hydrocarbon (HC) oxidation performance is known to be strongly affected by the HC species present and the catalyst design. However, the engine operating conditions and additive fuel supply parameters also affect the oxidation performance of DOCs, but the effects of these variables have been insufficiently examined. Therefore, in this study, the oxidation performance of a DOC was examined in experiments in which both exhaust gas recirculation (EGR) levels and exhaust pipe injection parameters were varied. The results were then analyzed and optimal conditions were identified using modeFRONTIER.

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.

For diesel emission control systems containing a Diesel Oxidation Catalyst (DOC) and a Catalyzed Soot Filter (CSF) the DOC is used to oxidize the additional fuel injected into the cylinder and/or the exhaust pipe for the purpose of increasing the CSF inlet temperature during the soot regeneration. Hydrocarbon (HC) oxidation performance of the DOC is affected by HC species as well as a catalyst design, i.e., precious metal species, support materials and additives. How engine-out HC species vary as a function of fuel supply conditions is not well understood. In addition, the relationship between catalyst design and oxidation activity of different hydrocarbon species requires further study. In this study, diesel fuel was supplied by in-cylinder, post injection and exhaust HC species were measured by a gas chromatograph-mass spectrometry (GC-MS) and a gas analyzer. The post injection timing was set to either 73°, 88° or 98° ATDC(after top dead center).

Three types of combustion chamber configurations (Types A, B, and C) with compression ratio lower than that of the baseline were tested for improved performance and exhaust gas emissions from an inline-four-cylinder 1.7-liter common-rail diesel engine manufactured for use with passenger cars. First, three combustion chambers were examined numerically using CFD code. Second, engine tests were conducted by using Type B combustion chamber, which is expected to have the best performance and exhaust gas emissions of all. As a result, 80% of NOx emissions at both low and medium loads at 1500 rpm, the engine speed used frequently in the actual city driving, improved with nearly no degradation in smoke emissions and brake thermal efficiency. It was shown that a large amount of cooled EGR enables NOx-free combustion with long ignition delay.

Urea-SCR system has a high NOx reduction potential in the steady-state diesel engine operation. In complicated transient operations, however, there are certain problems with the urea-SCR system in that NOx reduction performance degrades and adsorbed NH3 would be emitted. Here, optimum urea injection methods and exhaust bypass control to overcome these problems are studied. This exhaust bypass control enables NO/NOx ratio at the inlet of SCR catalyst to be decreased widely, which prevents over production of NO2 at the pre-oxidation catalyst. Steady-state and simple transient engine tests were conducted to clarify NOx reduction characteristics when optimum urea injection pattern and exhaust bypass control were applied. In simple transient test, only the engine load was rapidly changed for obtaining the fundamental knowledge concerning the effect of those techniques.

A variable valve timing (VVT) mechanism was applied to achieve premixed diesel combustion at higher load for low emissions and high thermal efficiency in a light duty diesel engine. By means of late intake valve closing (LIVC), compressed gas temperatures near the top dead center are lowered, thereby preventing too early ignition and increasing ignition delay to enhance fuel-air mixing. The variability of effective compression ratio has significant potential for ignition timing control of conventional diesel fuel mixtures. At the same time, the expansion ratio is kept constant to ensure thermal efficiency. Combining the control of LIVC, EGR, supercharging systems and high-pressure fuel injection equipment can simultaneously reduce NOx and smoke. The NOx and smoke suppression mechanism in the premixed diesel combustion was analyzed using the 3D-CFD code combined with detailed chemistry.

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.