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Reducing the emissions and fuel consumption of a spark ignition engine by utilizing heat exchangers in the exhaust gas stream

In this study, an analytical technique has been used to design four types of heat exchanger in a spark ignition engine in an attempt to reduce both the warm-up period and the exhaust gas temperature under high-load conditions. The heat exchangers are installed in two different positions. One is installed after the outlet of the close-coupled catalytic converter to reduce the warm-up period, using the exhaust gas energy, and the other is installed between the exhaust manifold and the inlet of the close-coupled catalytic converter to avoid thermal ageing. To increase the heat transfer between the exhaust gas and the engine coolant, internally finned tubes have been selected. The first and second laws of thermodynamics are applied to optimize the number of fins and their geometry (i.e. the height and the thickness). Finally, the impact of heat exchangers on the warm-up period and the catalyst inlet temperature at high loads are presented. The results indicate that both the warm-up period and the exhaust gas temperature are decreased when the heat exchangers are installed along the exhaust gas stream. The results also show that a heat exchanger in the exhaust gas stream has the potential to reduce the requirement for high-load component-protection fuelling which, in turn, results in reduced fuel consumption and emissions.