Design of a heat exchanger to reduce the exhaust temperature in a spark-ignition engine

A design of experiments (DOE) technique was used to design an exhaust heat exchanger to reduce the exhaust gas temperature under high load conditions in a spark-ignition engine. Through a limited number of experiments, the DOE evaluated the influence and the interaction of eight selected design parameters of the heat exchanger that affect the cooling performance of the exhaust gas. The heat exchanger was installed between the exhaust manifold and the inlet of the close-coupled catalytic converter (CCC) to avoid thermal aging. To maximize the heat transfer between the exhaust gas and coolant, fins were implemented at the inner surface of the heat exchanger. The design parameters consisted of the fin geometry (i.e., length, thickness, arrangement, and number of fins), coolant direction, exchanger wall thickness, and the length of the heat exchanger. The DOE results were analyzed and the acceptable range of each design parameter is discussed.