Effect of Exhaust Gas Temperature Limits on the Peak Power Performance of a Turbocharged Gasoline Engine

Peak power of an engine is typically constrained by the maximum obtainable airflow. This constraint could arise directly from the airflow limitation imposed by the throttle restriction (typical for a naturally aspirated engine), or indirectly from other factors, such as various temperature limits for component protection. In this work, we evaluate the airflow limit for a turbocharged gasoline engine as dictated by the constraints on the turbine inlet temperature. Increasing the limit on the turbine inlet temperature requires the exhaust manifolds and turbine to be made out of more expensive materials that withstand higher temperatures. This expense is justifiable if operating with higher turbine inlet temperature allows noticeably higher power output, and not merely increases the allowable airflow. Experimental data show that under some conditions the increase in airflow does not increase the peak power. The effects of increasing airflow on the peak power and turbine inlet temperatures are systematically analyzed through individual accounting for the different losses affecting the engine torque. The breakdown analysis presented in this work indicates combustion phasing as a major contributing factor to whether increasing the flange temperature limit would increase the peak power.