An important goal in diesel engine research is the development of a means to reduce the emissions of nitrogen oxides (NOx). The use of a cooled exhaust gas recirculation (EGR) system is one of the most effective techniques currently available for reducing nitrogen oxides. Since PM (Particulate Matter) fouling reduces the efficiency of an EGR cooler, a tradeoff exists between the amount of NOx and PM emissions, especially at high engine loads. In the present study, we performed engine dynamometer experiments and numerical analyses to investigate how the internal shape of an EGR cooler affects the heat exchanger efficiency. Heat exchanger efficiencies were examined for plain and spiral EGR coolers. The temperature and pressure distributions inside these EGR coolers were obtained in three dimensions using the numerical package program FLUENT.

We have developed a highly efficient boiler system using the 930 cc diesel engine. In this system, the co-generation concept is utilized in that the electric power is produced by the generator connected to the diesel engine, and waste heat is recovered from both the exhaust gases and the engine itself by the finned tube and shell & tube heat exchangers. A specially designed secondary combustor is installed at the engine outlet in order to completely reignite the unburned fuel from the diesel engine, thereby improving a system’s efficiency as well as reducing air pollution due to exhaust gases. It is found that the total efficiency (thermal efficiency plus electric power generation efficiency) of this system reaches maximum 94.4% which is about 20% higher than the typical diesel engine boiler system currently being used worldwide.