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Cooling heat loss is one of the most dominant losses among the various engine losses to be reduced. Although many attempts to reduce it by insulating the combustion chamber wall have been carried out, most of them have not been successful. Charge air heating by the constantly high temperature insulating wall is a significant issue, because it deteriorates charging efficiency, increases the emissions of soot and NOx in diesel engines, and promotes the knock occurrence tendency in gasoline engines. A new concept heat insulation methodology which can reduce cooling heat loss without heating the charging air has been developed. Surface temperature of insulation coating on the combustion chamber wall changes rapidly, according to the quickly changing in-cylinder gas temperature in each engine stroke. During the compression and expansion stroke, the surface temperature of the insulation coating goes up rapidly, and consequently, the heat transfer becomes lower by the reduced temperature difference between the surface and the gas. During the intake stroke, the surface temperature goes down rapidly, and it prevents intake air heating from the wall. To realize the above-mentioned functionality, a thin coating layer with low thermal conductivity and low heat capacity was developed. It was applied on the pistons of diesel engines, and showed improvement in thermal efficiency. It also showed a reduction of unburnt fuel emission in low temperature engine starting condition. The energy balance analysis showed reduction of cooling heat loss and, on the contrary, increase in the brake power and the exhaust loss.

Supplemental material, Contributor_Form for Thermo-swing insulation to reduce heat loss from the combustion chamber wall of a diesel engine by Akio Kawaguchi, Yoshifumi Wakisaka, Naoki Nishikawa, Hidemasa Kosaka, Hideo Yamashita, Chikanori Yamashita, Hiroki Iguma, Kenji Fukui, Noriyuki Takada and Terutoshi Tomoda in International Journal of Engine Research

Low-pressure loop exhaust gas recirculation systems are effective means of simultaneously reducing the NOx emissions and fuel consumption of diesel engines. Further lower emission levels can be achieved by adopting a system that combines low-pressure loop exhaust gas recirculation with a NOx storage and reduction catalyst. However, this combined system has to overcome the issue of combustion fluctuations resulting from changes in the air–fuel ratio due to exhaust gas recirculation from rich operating conditions. The aim of this research was to reduce combustion fluctuations by developing low-pressure loop exhaust gas recirculation control logic. In order to control the combustion fluctuations caused by low-pressure loop exhaust gas recirculation, it is necessary to estimate the recirculation time. First, recirculation delay was investigated, and a model was developed. A good correlation was found between actual measurements and the recirculation delay estimated by this model. Next, the control logic for low-pressure loop exhaust gas recirculation was studied. The recirculation gas under rich operating conditions was detected by an air–fuel ratio sensor to examine a method of controlling the exhaust gas recirculation valve in accordance with the timing for the rich gas to reach the exhaust gas recirculation valve actually. Thus, fluctuations in torque and combustion noise were improved.

The effects of variable valve timing and lift are studied in order to improve the thermal efficiency of a diesel engine, while maintaining low emission levels. At high load conditions, early closing of one of the intake valves or early intake valve opening realizes an enhancement of swirl intensity without increased pumping losses, and retarded intake valve closing reduces the effective compression ratio, both of which result in an increased exhaust gas recirculation ratio and an advanced fuel injection timing. Consequently low NO x formation and an improved thermal efficiency can be achieved simultaneously. At low load conditions, the injected fuel is dispersed in the cylinder by air swirl because of the small fuel quantity, and the increased effective compression ratio achieved by the early intake valve closing becomes effective at reducing hydrocarbon emissions. It is confirmed that the variable valve timing and lift system introduced in this research can flexibly change the engine parameters that govern engine combustion at various engine operating conditions. As a result, a 40 per cent reduction of engine-out NO x emissions and 4 per cent improvement of fuel consumption in the New European Driving Cycle (NEDC) are achieved. Furthermore, low-end torque could be increased by 40 per cent, utilizing exhaust pressure pulsation by matching of exhaust valve opening timing, and the overlap of intake and exhaust valve opening around top dead centre in the intake stroke. To enhance these benefits a new piston chamber with deep valve pockets is developed and its effect is investigated.

The purpose of this study is to make a numerical model that predicts the spray characteristics of a wall impingement injector. The film flow on the wall was analyzed theoretically using the laminar boundary-layer model. The biquadratic velocity profile was employed for the laminar boundary layer. The thickness of the liquid film on the wall was measured by an automatic thickness measurement system, which was newly developed for the present study and is based on the contact needle method. From the measurements, the film thickness decreased first toward the periphery, and then increased along the line that was perpendicular to the liquid injection direction. The theoretical analysis of the film thickness on the wall agreed well with the measurements. The sizes of the droplets from the newly developed wall impingement injector were predicted by using the proposed theoretical analysis of a film flow and the existing liquid-film breakup model. From the measurements from the phase Doppler particle analyzer, the mean droplet size decreased once toward the spray periphery and then increased. This trend of the droplet size was coincident to that of the liquid-film thickness at the edge of the wall. The mean droplet size decreased as the liquid injection pressure increased. The predictions of the droplet size agreed well with the measurements.

The influences of fuel vaporization on the stratified mixture preparation of a direct injection gasoline engine were investigated by means of altering fuel property. Iso pentane was selected for the evaluation. The mixture preparation in the both case of gasoline and iso pentane were numerically simulated with 3-D CFD. The experimental examinations, such as engine performance tests, the incylinder visualization and the cylinder pressure analysis, were also given. It was confirmed that the iso-pentane vaporized much quicker than gasoline, whereas there were not many differences in the fuel distribution at the ignition timing. Therefore, the effect of the injection timing on the indicated mean effective pressure, exhaust NOx and HC emissions and the heat release rate was almost same between the two fuels.

A direct injection gasoline engine employing a new stratified combustion system has been developed. A fan-shaped fuel spray and a shell-shaped piston cavity achieved the combustion strategy. The process of stratified mixture formation and consequent stratified combustion is affected by the fuel spray characteristics, therefore numerical analysis (CFD) was applied to understand the phenomena of mixture formation process. From the results of CFD, it was clarified that the vaporization characteristic is important in realizing a suitable stratified mixture formation, in addition to the spray liquid characteristics, and CFD enables prediction and analysis of actual phenomena.

A three-dimensional simulation technique for the stratified combustion process in direct injection gasoline engines is developed. The effects of a widely distributed mixture equivalence ratio and a large amount of EGR on laminar flame speed are briefly modeled taking into account only the temperature of the unburned mixture and the flame temperature. The suggested laminar flame speed model is incorporated into a CFD code in combination with the coherent flame model. In burned gas, chemical equilibrium depending on the local equivalence ratio is assumed so that the post flame reaction upon mixing rich burned gas and lean burned gas or fresh air can be simply modeled as a change of the equilibrium. The calculated flame propagation process, heat release rate and exhaust emissions are confirmed by the results of measurements including the LIF technique. The good agreements obtained under various conditions indicate the applicability of this method.

An instrument to measure time-resolved fuel–air ratio in the vicinity of a spark plug was developed. Properties of absorption and scattering at the wavelengths of visible and infrared rays were utilized to determine the fuel–air ratio in the mixture including liquid and vaporized fuel. The measurement error of the instrument was within 10% as a result of comparison between the overall and the measured fuel–air ratio at the vicinity of the spark plug under the inlet port injection, which forms a relatively homogeneous mixture. The instrument was applied to a direct injection gasoline engine and the mixture formation process was clarified.

An instrument to measure time-resolved fuel-air ratios in the vicinity of a spark plug was developed. Absorption and scattering at the wavelengths of visible and infrared rays were utilized to determine the fuel-air ratios in the mixture including liquid and vaporized fuel. The measurement error of the instrument was estimated within 10% from comparison between the overall and the measured fuel-air ratios at the vicinity of the spark plug with inlet port injection which froms homogeneous mixture. The instrument was applied to direct injection gasoline engines and the mixture formation process was discussed.