Analysis on the heat exchanger to reduce the exhaust gas tempertaure in a spark-ignition engine

Abstract

To meet stringent emissions standards, a considerable amount of development is necessary to ensure the suitable efficiency and durability of catalyst systems in SI engines. The main challenge is to reduce the engine cold-start emissions. Closed-coupled catalyst (CCC) provides fast light-off time by utilizing the energy in the exhaust gas. The close-coupled catalyst performance should satisfy ULEV emission levels after aging at 1050℃ for 24 hours. However, if some malfunctions occurred at engine operation and the catalyst temperature exceeds the 1050℃, the catalytic converter is deactivated and shows the poor conversion efficiency. In that situation, excess fuel is injected intentionally to lower the exhaust temperature. Hence, it resulted in worse fuel economy. In this work, the exhaust cooling system was proposed to lower the exhaust temperature in an SI engine. The heat exchanger was installed between exhaust manifold and the inlet of close-coupled catalytic converter (CCC) to avoid the thermal aging. The exhaust heat exchanger successfully decreased the exhaust gas temperature, which eliminated the requirement of fuel enrichment under high load conditions. However, cooling of exhaust gas through the heat exchanger may cause the deterioration of exhaust emissions at cold start due to the increment of catalyst light-off time. The light-off time was found to increase by 18 seconds in EC mode test. Hydrocarbon emission was also increased by 0.021g/km through it still meets the Euro-IV regulation. The fuel economy was improved by 7.64% at high speed condition owing to no fuel enrichment. The cooling systems in exhaust manifold were developed and cooling efficiencies were compared. The heat flux from the exhaust gas into the coolant in the heat exchanger was calculated using the measured coolant temperatures. Exhaust gas temperatures were calculated analytically as a function of engine speed and load. Surface temperature distribution in exhaust manifold was also c...