Effects of Aerodynamics on Fuel Consumption of a Multivalve S-I Engine. Investigation of the Instantaneous Local Heat Transfer at Part Loads and Distinct Equivalence Ratios

The purpose of this study is to outline the effects of aerodynamics on the heat losses of a S.I. multivalve engine and to link these results with the energetic efficiency of the engine. For that aim, we measured the local and instantaneous heat transfer in a 1.6 1 spark-ignited engine with several heat flux probes inserted in the cylinder head and in the liner of the combustion chamber. Two different cylinder heads were instrumented. They allowed to create distinct air motion configurations (baseline without structured flow, swirl and two levels of tumble). Furthermore, the pressure history was determined in the same cylinder than the heat transfer measurements. For all these configurations, we used a large range of operating conditions including several part loads, distinct equivalence ratios and two different engine speeds.

Local heat transfer measurements on firing conditions showed clearly that the cycle by cycle and spatial variations, are directly linked to the flame propagation and that local heat losses increase with swirl and tumble. Moreover, the fuel consumption of the S.I. engine increases with air motion at low loads and under lean-burn conditions. The tendency is more significant for a tumble configuration.