Due to global warming and depletion of fossil fuels, technologies reducing CO2 emission and increasing fuel efficiency simultaneously are required. Exhaust heat recovery system converting exhaust heat energy into an electrical energy or mechanical energy can significantly reduce fuel consumption. But those devices reduce the exhaust pipe opening area and increase the exhaust gas pressure. The pressure increase disturbs a gas flow out and makes a bad effect on the engine performance.
To understand the effects, an engine performance is measured with various opening ratios. The result shows that the fuel consumption rate is reduced in case of little amount of the pressure increase, and NOX is reduced with the pressure increase, while the concentration of the toxic exhaust gases are increased in the case of high back-pressure.
Three types of heat exchangers installed on a exhaust pipe are tested. In the case of plate type heat exchanger, back pressure became highest and maximum cylinder pressure reduced in low speed and 100% load. And back pressure increased over twice and fuel consumption also increased up to 2%, which was the highest increasing rate. In the case of fin tube, the amounts of exhaust emissions and fuel consumption rate were less than the other two cases. The effect of shell and tube was in the middle. Making a decision by the effect on engine performance, a fin tube type is the best for exhaust heat recovery systems.
Exhaust gas heat input and recovery by a heat exchanger are finally studied. Shell-and-tube type heat exchanger has a high heat recovery at low speed, and plate type has the effect of high recovery at high speed. However, fuel consumption of the engine increased rapidly. In the case of fin-tube type, high efficiency of the heat exchanger at the high-speed and middle-speed is shown, and averaged power increases by 26.9% and averaged fuel efficiency improved up to 8.9%. Fin-tube type heat exchanger is expected as the best among the three types for the exhaust gas heat recovery system.