Factorial Analysis of Otto Cycle Engine Operating Parameters on the Exhaust Gases Temperature

Internal combustion engines are thermal machines that produce work by burning fuel and have a high power-to-weight ratio. A large part of the energy released in the combustion is lost with the exhaust gases and therefore is not converted to useful work. Thus, the understanding of the effects of engine operating factors such as rotation, type of fuel and type of coolant fluid on exhaust gases temperature, which is related to their specific enthalpy, allows optimizing engine performance. In this work, the operating parameters effect on the exhaust temperature were evaluated by means of a 2k factorial design of test runs performed on a Renault CLIO 1.6 Total Flex engine installed in a test bench. The factorial effects were evaluated using the ANOVA method with a significance level of 5%. The investigated factors levels were: rotation (1500 rpm and 3000 rpm), fuel (alcohol and gasoline), coolant (water without additive and water with additive). The results showed that an increase in rotation and the substitution of alcohol by gasoline increase the exhaust gases temperature, which increases the specific energy of the flow leaving the engine by convection. In addition, the interaction effect of these parameters is also significant, which reduces the use of available energy in the fuel. The coolant factor did not have a significant effect; however, the effect of the interaction between coolant type and fuel type had a significant influence on the exhaust temperature, indicating that the type of fluid ideal for an engine may depend on the type of fuel used.