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Effects of Exhaust Gas Recirculation on Performance of a 49 cc Spark Ignited Engine

  • Author(s): KIM, SOUNG UK
  • Advisor(s): Dunn-Rankin, Derek
  • et al.

Exhaust gas recirculation (EGR) is a proven and effective strategy for reducing the nitrogen oxides (NOx) emission of automotive-scale internal combustion engines. NOx formation is highly correlated with conditions when the flame temperature in the combustion chamber of the engine exceeds 1900K. The EGR method recirculates some of the exhaust gas back into the intake manifold where it mixes with the fresh intake air. The exhaust gases dilute the oxygen but provide some sensible heat, thereby reducing peak flame temperatures but helping to maintain combustion stability. This work is novel in its application of a customized EGR system to a 49 cc engine, where the single cylinder and small scale make its performance particularly susceptible to combustion upsets. The reduction of combustion and exhaust gas temperatures resulted in a 642ppm reduction of NOx (77.3%) at 6000 RPM with an EGR rate of 11.7%. Thus EGR was very effective for reduced NOx emission, but it resulted in typical penalties of EGR including a slight increase in fuel consumption at all RPM conditions (8.6mg/s (8.7%) at 2100 RPM to 2.6mg/s (9.8%) at 6000 RPM) and a slight decrease in engine torque and power at high RPM conditions (0.14N·m at 4000 RPM to 0.59N·m at 6000 RPM and 0.06 HP at 4000 RPM to 0.37 HP at 6000 RPM). Hence, there was the trade-off between gas emission and the pollutant emissions and performance penalties.

There is an optimal and applicable range of EGR rate, 7.5% - 12%, at these speeds when considering the ratio of exhaust gas temperature and engine coolant temperature (E/C Temperature Ratio) appropriate for extending the life of the engine with EGR. In addition, an EGR rate was found at the high RPM that maximized the advantages of the reduction of NOx, CO, and HC and minimized the disadvantages of decreasing the engine torque, power, and fuel consumption. An experimental investigation on pollutant emissions and performance of a small (49 cc) single cylinder, four stroke, port fuel injection, spark ignited engine was conducted to observe and analyze the effects of EGR. EGR in such a small engine experimental testbed configuration has not been studied before, and through the research a customized EGR concept consisting of an EGR copper pipe system (Hot EGR system), which is necessary for effective small engine use of EGR, was developed.

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