Experiments on the influence of intake conditions on local instantaneous heat flux in reciprocating internal combustion engines

The present study tries to be a contribution for the development of more precise theoretical models for predicting the dissipation of heat through the combustion chamber walls of reciprocating (internal combustion) IC engines. A fast response thermocouple was embedded in the combustion chamber of a single cylinder engine to measure instantaneous wall temperatures. The heat flux was obtained by solving the one-dimensional transient energy equation with transient boundary conditions using the Fast Fourier Transform. The engine was tested under different operating conditions to evaluate the sensitivity of the measurement procedure to variations of three relevant combustion parameters: injection pressure, air temperature and oxygen concentration at the intake. The local heat flux obtained was compared with other relevant parameters that characterize the thermal behaviour of engines, showing, in most of the cases, correlation among them. The results showed that the instantaneous heat flux through the walls and hence the local wall temperatures are strongly affected by the ignition delay and the start of combustion.

Research highlights
► The consideration of the chamber wall as a semi-infinite body and one-dimensional heat transfer is a suitable approach to measure the instantaneous heat flux in (internal combustion) IC engines.
► The instantaneous heat flux through the walls and the local wall temperatures are strongly affected by the ignition delay.
► EGR (exhaust gas recirculation) rate has a strong influence on instantaneous heat flux.
► The effect of EGR rate on the indicated efficiency and local heat flux is reduced as the intake temperature increases.