Terutoshi Tomoda

Improvement of diesel engine performance by variable valve train system

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.

Development of instrument for measurement of fuel-air ratio in vicinity of spark plug : application to DI gasoline engine

Abstract 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.

Prediction of Mean Droplet Size of Sprays Issued from Wall Impingement Injector

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.

Modeling of Wall Impinging Behavior with a Fan Shaped Spray

The experiment-based droplet impinging breakup model was applied to a fan shaped spray and the impinging behavior was analyzed quantitatively. Evaluation of the quantitative results with validation tests verified the following. The model enables prediction of fan shaped spray thickness after Impingement caused by the breakup of fuel droplets, which could not be represented with the Wall-Jet model, widely used at present. Fuel film movement on a wall is negligible when the injection pressure of the fan shaped spray is high and the spray travelling length is not too short. The proposed heat transfer coefficient between fuel film and the wall is too small to represent the vaporizing rate of the fuel film.

A control strategy of low-pressure loop exhaust gas recirculation and NOx storage catalyst for diesel engines

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.

Development of Instrument for Measurement of Fuel-Air Ratio in the Vicinity of Spark Plug. Application to DI Gasoline Engines.

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.