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The first objective of this work is to develop a numerical simulation model of the spark ignited (SI) engine combustion, taking into account knock avoidance and heat transfer between in-cylinder gas and combustion chamber wall. Secondly, the model was utilized to investigate the potential of reducing heat losses by applying a heat insulation coating to the combustion chamber wall, thereby improving engine thermal efficiency. A reduction in heat losses is related to important operating factors of improving SI engine thermal efficiency. However, reducing heat losses tends to accompany increased combustion chamber wall temperatures, resulting in the onset of knock in SI engines. Thus, the numerical model was intended to make it possible to investigate the interaction of the heat losses and knock occurrence. The present paper consists of Part 1 and 2.

The objective of this work is to develop a numerical simulation model of spark ignited (SI) engine combustion and thereby to investigate the possibility of reducing heat losses and improving thermal efficiency by applying a low thermal conductivity and specific heat material, so-called heat insulation coating, to the combustion chamber wall surface. A reduction in heat loss is very important for improving SI engine thermal efficiency. However, reducing heat losses tends to increase combustion chamber wall temperatures, resulting in the onset of knock in SI engines. Thus, the numerical model made it possible to investigate the interaction of the heat losses and knock occurrence and to optimize spark ignition timing to achieve higher efficiency. Part 2 of this work deals with the investigations on the effects of heat insulation coatings applied to the combustion chamber wall surfaces on heat losses, knock occurrence and thermal efficiency.

Natural gas has been used in spark-ignition (SI) engines of natural gas vehicles (NGVs) due to its resource availability and stable price compared to gasoline. It has the potential to reduce carbon monoxide emissions from the SI engines due to its high hydrogen-to-carbon ratio. However, short running distance is an issue of the NGVs. In this work, methodologies to improve the fuel economy of a heavy-duty commercial truck under the Japanese Heavy-Duty Driving Cycle (JE05) is proposed by numerical 1D-CFD modeling. The main objective is a comparative analysis to find an optimal fuel economy under three variable mechanisms, variable valve timing (VVT), variable valve actuation (VVA), and variable compression ratio (VCR). Experimental data are taken from a six-cylinder turbocharged SI engine fueled by city gas 13A. The 9.83 L production engine is a CR11 type with a multi-point injection system operated under a stoichiometric mixture.

The purpose of the present study is to find a way to extend a combustion stability limit for diluted combustion in a spark-ignition (SI) gasoline engine which has a high compression ratio. This paper focuses on partial oxidation in an unburned mixture which is observed in the high compression engine and clarifies the effect of partial oxidation in an unburned mixture on the behavior of a flame stretch and the extinction limit. The behavior of the flame stretch was simulated using the detailed chemical kinetics simulation with the opposed-flow flame reactor model. In the simulation, the reactants which have various reaction progress variables were examined to simulate the flame stretch and extinction under the partial oxidation conditions. The mixtures were also diluted by complete combustion products which represent exhaust gas recirculation (EGR).

We have proposed the engine featuring a new compressive combustion principle based on pulsed supermulti-jets colliding through a focusing process in which the jets are injected from the chamber walls to the chamber center. This principle has the potential for achieving relatively silent high compression around the chamber center because autoignition occurs far from the chamber walls and also for stabilizing ignition due to this plug-less approach without heat loss on mechanical plugs including compulsory plasma ignition systems. Then, burned high temperature gas is encased by nearly complete air insulation, because the compressive flow shrinking in focusing process gets over expansion flow generated by combustion.

This paper describes the development of an integrated simulation model for evaluating the effects of electrically heating the three-way catalyst (TWC) in a series hybrid electric vehicle (s-HEV) on fuel economy and exhaust gas purification performance. Engine and TWC models were developed in GT-Power to predict exhaust emissions during transient operation. These models were validated against data from vehicle tests using a chassis dynamometer and integrated into an s-HEV model built in MATLAB/Simulink. The s-HEV model accurately reproduced the performance characteristics of the vehicle’s engine, motor, generator, and battery during WLTC mode operation. It can thus be used to predict the fuel consumption, emissions, and performance of individual powertrain components. The engine combustion characteristics were reproduced with reasonable accuracy for the first 50 combustion cycles, representing the cold-start condition of the driving mode.

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 ultra lightweight compact vehicle named “the Waseda Future Vehicle” has been designed and developed, aiming at a simultaneous achievement of low exhaust gas emissions, high fuel economy and driving performance. The vehicle is powered by a dual-type hybrid system having a SI engine, electric motor and generator. A high performance lithium-ion battery unit is used for electricity storage. A variety of driving cycles were reproduced using the hybrid vehicle on a chassis dynamometer. By changing the logics and parameters in the electronic control unit (ECU) of the engine, a significant improvement in emissions was possible, achieving a very high fuel economy of 34 km/h at the Japanese 10-15 drive mode. At the same time, a numerical simulation model has been developed to predict fuel economy. This would be very useful in determining design factors and optimizing operating conditions in the hybrid power system.

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.

Computational and theoretical analyses for a new type of engine (Fugine), which was proposed by us based on the colliding of pulsed supermulti-jets, indicate a potential for very high thermal efficiencies and also less combustion noise. Three types of prototype engines were developed. One of them has a low-cost gasoline injector installed in the suction port and a double piston system in which eight octagonal supermulti-jets are injected and collide. Combustion experiments conducted on the prototype gasoline engine show high thermal efficiency comparable to that of diesel engines and less combustion noise comparable to that of traditional spark-ignition gasoline engines. This paper presents some combustion experiments of one of the other piston-less prototype engines having bi-octagonal pulsed multi-jets injected from fourteen nozzles.

A single-point autoignition gasoline engine (Fugine) proposed by us previously has a strongly asymmetric double piston unit without poppet valves, in which pulsed multi-jets injected from eight suction nozzles collide around the combustion chamber center. Combustion experiments conducted on this engine at a low operating speed of 2000 rpm using gasoline as the test fuel under lean burn conditions showed both high thermal efficiency comparable to that of diesel engines and silent combustion comparable to that of conventional spark-ignition gasoline engines. This gasoline engine was tested with a weak level of point compression generated by negative pressure of about 0.04 MPa and also at an additional mechanical homogeneous compression ratio of about 8:1 without throttle valves. After single-point autoignition, turbulent flame propagation may occur at the later stage of heat release.

In recent years, a new type of engine (Fugine) based on the colliding of pulsed supermulti-jets was proposed by us, which indicates the potential for attaining very high thermal efficiencies and also less combustion noise. A prototype engine with eight nozzles for injecting octagonal pulsed supermulti-jets, which was developed with a low-cost gasoline injector and a double piston system, showed high thermal efficiency comparable to that of diesel engines and also less combustion noise comparable to that of traditional spark-ignition gasoline engines. Another type of prototype piston-less engine having fourteen bioctagonal nozzles was also developed and test results confirmed the occurrence of combustion, albeit it was unstable. In this work, time histories of pressure were measured in the combustion chamber of the piston-less prototype engine under a cold flow condition without combustion in order to examine the compression level obtained with the colliding supermulti-jets.

A new engine concept (Fugine) based on colliding pulsed supermulti-jets was proposed in recent years, which is expected to provide high thermal efficiencies over 50% and less combustion noise. Theoretical analyses indicate a high potential for thermal efficiency over 60%. Three types of prototype engines have been developed. The first prototype engine based only on the colliding of pulsed supermulti-jets with fourteen nozzles has no piston compression, while the second type equipped with a low-cost gasoline injector in the suction port has a double piston system and eight jet nozzles. Combustion experiments conducted on the second prototype gasoline engine show high thermal efficiency similar to that of traditional diesel engines and lower combustion noise comparable to that of traditional spark-ignition gasoline engines.

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.

For various densities of gas jets including very light hydrogen and relatively heavy ones, the penetration length and diffusion process of a single high-speed gas fuel jet injected into air are computed by performing a large eddy simulation (LES) with fewer arbitrary constants applied for the unsteady three-dimensional compressible Navier-Stokes equation. In contrast, traditional ensemble models such as the Reynolds-averaged Navier-Stokes (RANS) equation have several arbitrary constants for fitting purposes. The cubic-interpolated pseudo-particle (CIP) method is employed for discretizing the nonlinear terms. Computations of single-component nitrogen and hydrogen jets were done under initial conditions of a fuel tank pressure of gas fuel = 10 MPa and back pressure of air = 3.5 MPa, i.e., the pressure level inside the combustion chamber after piston compression in the engine.

The necessity of the reduction of the lubricating oil consumption of diesel engines has been increasing its importance to reduce the negative effect of exhausted oil on after treatment devices for exhausted gas. The final purpose of the studies is clarifying the mechanism of the oil consumption and developing the method of its estimation. For the basic study, the mechanism of oil film generation on the piston skirt could be explained by hydrodynamic lubrication in our first and second reports [1, 2]. In this paper, the piston skirt was calculated using the measured piston motion to clarify the effect of the piston motion to the piston skirt oil film behavior.

Clarifying the mechanism of the oil consumption of engines is necessary for developing its estimation method. Oil moves upwards on the piston to the combustion chamber through ring sliding surfaces, ring backs and ring gaps. The mechanisms of oil upwards transport through the ring gaps are hardly analyzed. In this report, oil pressure just under the oil ring was successfully measured by newly developed method to clarify the oil transport mechanism at the ring gap. It was showed that the generated oil pressure pushed up the oil at the ring gap.

The requirement for the reduction of lubricating oil consumption of diesel engines has become increasingly important in reducing the effect of exhausted oil on after treatment devices for exhaust gas. In our first report, findings indicated that piston skirt length affected oil consumption, and they clearly showed that the oil film on the piston skirt should be considered in the calculation for oil consumption. In this report, the mechanism of oil film generation on the piston skirt is investigated. The oil film on the piston skirt is calculated and the effect of piston motion on the oil film region is clarified, i.e., considering the piston rotation around the top of the piston skirt at the anti-thrust side is important for the calculation of the oil film region.

Much effort has been devoted to studies on auto-ignition engines of gasoline including homogeneous-charge combustion ignition engines over 30 years, which will lead to lower exhaust energy loss due to high-compression ratio and less dissipation loss due to throttle-less device. However, the big problem underlying gasoline auto-ignition is knocking phenomenon leading to strong noise and vibration. In order to overcome this problem, we propose the principle of colliding pulsed supermulti-jets. In a prototype engine developed by us, octagonal pulsed supermulti-jets collide and compress the air around the center point of combustion chamber, which leads to a hot spot area far from chamber walls. After generating the hot spot area, the mechanical compression of an asymmetric double piston unit is added in four-stroke operation, which brings auto-ignition of gasoline.

An inexpensive, lightweight, and relatively quiet engine reactor that has the potential to achieve thermal efficiency over 50% for small engines was proposed in our previous reports, which is achieved with colliding supermulti-jets that create air insulation to encase burned gas around the chamber center, avoiding contact with the chamber walls and piston surfaces. The colliding of pulse jets can maintain high pressure ratio for various air-fuel ratios, whereas traditional homogeneous compression engines due to piston cannot get high pressure ratio at stoichiometric condition. Emphasis is also placed on the fact that higher compression in this engine results in less combustion noise because of encasing effect. Here, a small prototype engine having supermulti-jets colliding with pulse and strongly-asymmetric double-piston system is examined by using computational experiments. Pulse can be generated by the double piston system of a short stroke of about 40mm.