Shuji Kimura

AN EXPERIMENTAL ANALYSIS OF LOW-TEMPERATURE AND PREMIXED COMBUSTION FOR SIMULTANEOUS REDUCTION OF NOX AND PARTICULATE EMISSIONS IN DIRECT INJECTION DIESEL ENGINES

Abstract A new combustion concept, named MK (modulated kinetics) combustion, has been developed, which reduces NOx and smoke simultaneously through high exhaust gas recirculation (EGR) and retarded injection timing. High-speed photography was employed to investigate the physical and chemical processes of MK combustion, and the results revealed that the combustion features premixed combustion and the low-temperature flames were accompanied by transparent appearances. Heat flux measurements and KIVA calculations were also made to investigate the effects of swirl, which serves to improve thermal efficiency in MK combustion. It was apparent that the swirl effectively governs the fuel distribution in the combustion chamber, suppressing HC formation and improving thermal efficiency by preventing the flames from contacting the cavity walls. Throughout these experiments, ignition delay and fuel injection duration were found to be the two key parameters that control MK combustion. Accordingly, ignition delay was prolonged by cooled EGR and fuel injection duration was shortened by high injection pressure to allow the MK combustion operation in a high load range.

Combination of Combustion Concept and Fuel Property for Ultra-Clean DI Diesel

Experimental investigations were previously conducted with a direct-injection diesel engine with the aim of reducing exhaust emissions, especially nitrogen oxides (NOx) and particulate matter (PM). As a result of that work, a combustion concept, called Modulated Kinetics (MK) combustion, was developed that reduces NOx and smoke simultaneously through low-temperature combustion and premixed combustion to achieve a cleaner diesel engine. In subsequent work, it was found that applying a low compression ratio was effective in expanding the MK combustion region on the high-load side. The MK concept was then combined with an exhaust after-treatment system and applied to a test vehicle. The results indicated the attainment of ULEV emission levels, albeit in laboratory evaluations. In the present work, the combination of the MK combustion concept and certain fuel properties has been experimentally investigated with the aim of reducing exhaust emissions further. The results indicated that the use of a high cetane number gas-to-liquid (GTL) fuel with a lower compression ratio provides a sufficiently long ignition delay to accomplish MK combustion. The effect on a simultaneous reduction of NOx and smoke was confirmed. The results also indicated that the use of GTL fuel can reduce the total hydrocarbon level substantially under a cold condition because of its good ignition characteristics, with a high cetane number and high levels of paraffin compounds. As a result, one possible approach to the attainment of SULEV emission levels was found.

Heat loss to the combustion chamber wall with deposit in D.I. diesel engine: variation of instantaneous heat flux on piston surface with deposit

Abstract Adhesion of deposit on the combustion chamber walls affects the state of the heat loss into combustion chamber wall surfaces in the internal combustion engine. In this study, as the first step, the instantaneous surface temperature and the instantaneous heat flux were measured by thin film thermocouples on piston surfaces in the D.I. diesel engine with the adhesion of deposit in order to clarify the effects of deposit. As a result, it is found that the instantaneous surface temperature and heat flux strongly depend on the amount of deposit adhered to the combustion chamber wall surfaces.

Internal flow analysis of nozzles for DI diesel engines using a cavitation model

Abstract A three-dimensional viscous flow analysis method using a cavitation model was applied to run internal flow calculations for the fuel injector nozzles of direct-injection diesel engines. It is especially notable that this method made it possible to examine and clarify the mechanism producing an asymmetrical spray from the valve covered orifice type nozzle under a small lift condition with an eccentric needle position. The calculated results for cavitation were compared with experimental data obtained by using a transparent model scaled up fivefold, and good qualitative agreement was seen between the two sets of data.

Development of noise reduction technologies for a small direct-injection diesel engine

Abstract The DI diesel engine has an advantage in terms of fuel economy, but disadvantages with respect to exhaust emissions and large combustion noise. To overcome these drawbacks, we have previously proposed the Modulated Kinetics (MK) concept [1] , [2] of low-temperature, premixed combustion. This paper presents the results of an investigation into the potential of a new combustion system to reduce combustion noise and improve emission performance simultaneously. As a result of applying heavy EGR and retarding the injection timing, combustion excitation forces are reduced without any increase in exhaust emissions, and with reduction of fuel injection system noise.

Three-dimensional computation of in-cylinder flow and combustion characteristics in diesel engines — Effect of wall impingement models of fuel droplet behavior on combustion characteristics

Abstract A computer code called TurboKIVA was used to perform three-dimensional computations to investigate the effects of fuel spray formation on the combustion and emission characteristics of direct and indirect injection diesel engines. As the first step, the code was modified to facilitate quantitative prediction of soot emissions and to improve prediction accuracy. An investigation was then made of the effects of fuel droplet wall impingement models on combustion characteristics. The results showed that combustion performance was influenced by the models, making it important to select a suitable wall impingement model in predicting NO x and soot emissions based on the operating conditions of IDI diesel engines.

Heat transfer coefficient on the combustion chamber wall surfaces in a naturally aspirated direct-injection diesel engine

Thin-film thermocouples were used to measure the instantaneous temperature at 100 points on all the combustion chamber wall surfaces in a naturally aspirated direct-injection diesel engine. Instantaneous heat flux at each measured point was also obtained through heat transfer analysis with the measured instantaneous wall surface temperature applied as a boundary condition. In addition, the instantaneous mass-averaged gas temperature in the combustion chamber was calculated through the equation of state of an ideal gas. As a result, the local and overall heat transfer coefficients were evaluated using the corresponding wall surface temperatures and heat fluxes. The overall heat transfer coefficients thus obtained were compared with those calculated with Eichelberg’s and Woschni’s empirical equations for five ignition timings and three engine speeds. As a result, it was revealed that an overall average heat transfer coefficient obtained through the authors’ experiments has characteristics different from those of the heat transfer coefficients calculated from the empirical equations proposed by Eichelberg and Woschni.

Development of new 4-valve/cylinder small DI diesel engine

Abstract Nitrous oxide (NO x ) and the particulate matter contained in the exhaust given off by diesel powered vehicles have been identified as elements responsible for polluting the atmosphere. As such, these emissions have been the targets of increasingly strict emission control regulations. Plans are underway to introduce regulations that are even stricter some time early in the next century. The advanced thermal efficiency offered by diesel engines is a feature clearly desired for its potential contribution toward energy conservation and the reduction of global warming. Research and development on the highly thermal-efficient direct-injection diesel engine are progressing at a rapid pace in Europe where introduction of a carbon dioxide tax is under consideration.

Knocking Prediction by Using Zero-Dimensional Engine Cycle Simulation with Chemical Kinetic Model

A zero-dimensional engine cycle simulation has been developed by implementing chemical kinetics as the auto-ignition model into the two-zone combustion chamber model. A mixed chemical reaction mechanism of the primary reference fuels is used. Experimental data have been carefully investigated to obtain correlation between calculated auto-ignition of the end-gas and actual knock intensity. The result shows that a combination of time of auto-ignition occurrence and heat release by auto-ignition can explain knock intensity. This correlation has been applied to the simulation so that it can predict knock occurrence including knock intensity. A number of calculations have been done under various engine parameters including compression ratio, intake temperature, octane rating and equivalence ratio. The results show that fair levels of agreements are obtained between calculated trace knock spark advance sensitivity and experimental trends.

Development of thin-film thermocouple measuring for instantaneous heat flux flowing into the ceramic combustion chamber wall

In order to evaluate the validity of a low heat rejection engine proposed for the reduction of heat loss, a thin film thermocouple was developed for accurate measurement of the instantaneous heat flux flowing into the ceramic combustion chamber wall. The thin film thermocouple is the pair-wire type construction without effects of the material of the thermocouple and the instantaneous heat flux, which was confirmed by finite element analysis. This paper also shows examples of measurements conducted on the instantaneous heat flux flowing into the ceramic combustion chamber, using the pairwire type thin film thermocouple made of ceramic base material.