Study on the waste heat recovery from exhaust gas of the naturally aspirated spark ignition engine

Abstract

The number of motor vehicles continues to grow globally and therefore increases reliance on the petroleum and increases the release of carbon dioxide into atmosphere which contributes to global warming. To overcome this trend, new vehicle technologies are introduced to achieve better fuel economy without increasing harmful emissions. For internal combustion engine (ICE) in most typical gasoline fuelled vehicles, it was estimated that 21% of the fuel energy is wasted through the exhaust at the most common load and speed range. The waste heat from exhaust gases represents a significant amount of heat energy, which has conventionally been used for combined heating and power applications. In this study, the waste heat recovery mechanism (WHRM) is developed for a naturally aspirated spark ignition engine. The performance of a naturally aspirated spark ignition engine equipped with the WHRM is explored, in terms of the engine performance and the generated power from WHRM. The experimental works were conducted by using an experimental vehicle, which implemented the WHRM on two mechanisms: gas turbine and steam turbine mechanisms. First, the experimental vehicle run on-road test without WHRM to explore the engine performance and the amount of heat energy from exhaust waste heat as a reference condition. Then, the experimental vehicle run on-road test with gas turbine mechanism steam turbine mechanism of WHRM. The major contributions of this study includes in conducting the experimental work of novel waste heat recovery mechanism, and implementing on the experimental vehicle (naturally aspirated spark ignition engine) with on-road test, which can reveal the performance of engine and waste heat recovery mechanism on the real condition. Heat energy from exhaust waste was found in range of 500 W up to 23 kW that obviously worthy to recover this heat energy. For WHRM, It is found that the gas turbine mechanism of waste heat recovery can reach up to 110 W, and occurs in short period of time around 1 to 4 second. Meanwhile the steam turbine mechanism can reach up to 29 W, but occurs in longer period of time, for example in 10 s. It also found that the gas turbine mechanism causes the power of engine to slightly drop, while the steam turbine mechanism of waste heat recovery does not affect the performance of engine. A new model for heat energy from exhaust waste heat and power generated from WHRM are proposed here to explain the possible enhancement, by using the engine speed, throttle angle, exhaust temperature, ambient temperature, and air flow rate as the data input in multiple regression method and Artificial Neural Network (ANN). For heat energy and both gas turbine and steam turbine mechanisms, the model of heat energy and generated power are found to be more in good agreement with experimental data using ANN with comparison to multiple regression method.