Search Results

Details of air flow in a direct injection diesel engine was investigated with a steady flow test rig. A laser doppler velocimeter was used to characterize the three dimensional air flow generated by two kinds of inlet ports. In order to obtain the distribution of flow velocity in a cylinder section, interpolation was carried out. A stereographic display of the three dimensional velocity vectors in the cylinder space allowed easy comprehension of the flow chracteristics. Angular momentum flux and turbulence kinetic energy in the region closer to the cylinder head as well as those in the lower region of the cylinder space are important for the prediction of air flow in an actual engine cylinder. Transition of the angular momentum flux along the cylinder axis is considered to be influenced by three kinds of angular momentum flux which is induced by an air jet around the inlet valve.

A mathematical model was developed for predicting the concentration of exhaust nitric oxide, soot and other emissions in a direct injection diesel engine. In the model, it was emphasized to describe the phenomena occurring in the combustion chamber from the microscopic point of view. The prediction was based on the knowledges concerning a single droplet as well as the droplet size distribution in a fuel spray and the spatial and temporal distribution histories of fuel in a combustion chamber. The heterogeneous field of temperature and equivalence ratio, and uniform pressure in the cylinder were postulated. The heat release model gives the burning rate of injected fuel and pressure and temperature history in the cylinder. The concentration of nitric oxide and soot in the cylinder was predicted by the emission formation model.

In this paper, the simulation of the multi-objective optimization problem of a diesel engine is performed using the phenomenological model of a diesel engine and the genetic algorithm. The target purpose functions are Specific fuel consumption, NOx, and Soot. The design variable is a shape of injection rate. In this research, we emphasize the following three topics by applying the optimization techniques to an emission problem of a diesel engine. Firstly, the multiple injections control the objectives. Secondly, the multi-objective optimization is very useful in an emission problem. Finally, the phenomenological model has a great advantage for optimization. The developed system is illustrated with the simulation examples.

In this study, a system to perform a parameter search of heavy-duty diesel engines is proposed. Recently, it has become essential to use design methodologies including computer simulations for diesel engines that have small amounts of NOx and SOOT while maintaining reasonable fuel economy. For this purpose, multi-objective optimization techniques should be used. Multi-objective optimization problems have several types of objectives and they should be minimized or maximized at the same time. There is often a trade-off relationship between objects and derivation of the Pareto optimum solutions that express the relationship between the objects is one of the goals in this case. The proposed system consists of a multi-objective genetic algorithm (MOGA) and phenomenological model. MOGA has strong search capability for Pareto optimum solutions. However, MOGA requires a large number of iterations.

In order to obtain a fundamental understanding of how soot forms and burns up during combustion in diesel engines, the relation between exhaust smoke level and combustion duration in direct injection diesel engine was measured. The effect of different injection timings, engine speeds and loads on combustion duration are presented and discussed. Combustion experiments in the less complex environment of a continuous spray open flame were performed from which soot samples were collected at various locations in the flame. By use of a special technique were obtained information on the mechanism of soot formation and oxidation could not be obtained from engine experiments. The similarity of soot formation and oxidation within diesel combustion chamber and continuous spray open flame are discussed. An analysis of these results shows that the exhaust smoke level is mainly determined by the concentration of soot at the time of exhaust valve opening, i.e. combustion duration is very important.

In this paper, a phenomenological simulation model has been developed to predict performance, thermal efficiency, pollutant emissions, and evaporating diesel spray distribution in the combustion chamber of a direct injection diesel engine. The model consists of two major parts, that is, the spray combustion model and the spray_distribution model. In the models, injected fuel spray is divided into many packages. Each package goes through such processes as fuel spray broken, droplet evaporation, air entrainment, flammable limit of mixture, and mixed air-fuel combustion, etc. The spray_combustion model also enabled to calculate subsequent spatial and temporal history of burning rate, local temperature, NO emission and soot. According to this information, distribution of temperature and mass of liquid and vapor fuels, and the wall impinging spray pattern in the combustion chamber were described three dimensionally using a 3-D volume rendering application by the spray distribution model.