Characterization of combustion and heat transfer in a direct injection spark ignition engine through measurements of instantaneous combustion chamber surface temperature

An experimental study was conducted to investigate combustion and in-cylinder heat transfer under different injection strategies in a direct injection spark ignition engine. Fast response heat flux probes on the piston and the cylinder head provided instantaneous surface temperature measurements at different locations. The combustion process was characterized based on heat release analysis, performance, and emissions. The experimental surface temperature variation during the engine cycle was used to calculate the heat flux based on Fourier analysis. Spatial variations of instantaneous surface temperature and heat flux were investigated for different injection strategies, engine speeds, and swirl intensities. Local heat fluxes were compared with global heat transfer correlations to better quantify spatial variations and evaluate validity of alternative heat transfer models. A new method for estimating flame arrival based on the time when the second derivative of the heat flux reaches a maximum value was proposed. Fuel impingement on the piston was detected by fast response heat flux probes when fuel was injected early during intake. The amount of fuel film on the piston was estimated by analyzing the heat loss due to fuel impingement and findings were augmented with the results of CFD calculations.; The results indicated much higher spatial variations of heat flux in the stratified mode than in the homogeneous mode. The trends varied with changing operating conditions, depending on air motion, mixing and flame propagation. In the stratified mode, the overall shape and phasing of the global heat flux based on the bulk gas temperature was not well correlated with local measurements, thus indicating deficiencies of classic heat transfer models when applied to these conditions. The heat flux derivative method for estimating flame arrival proved to be more robust and accurate than the other three methods considered. In the stratified operating mode, flame arrives at locations in the piston bowl almost simultaneously, while the surface temperature swings at the periphery are driven more by charge compression than flame effects. Combining experimental measurement of fuel film impingement and the CFD simulation indicated that the fuel film evaporation process was extremely fast when fuel was injected during the intake process.