Combustion and Heat Transfer Studies in a Spark-Ignited Multivalve Optical Engine 900353

The application of sophisticated analytical techniques for the design of spark-ignition engines has brought about the need for detailed information on the heat transfer processes in these engines. This study utilized time-resolved heat-flux measurements, heat-release analysis and high-speed flame photography to investigate experimentally the combustion and heat-transfer characteristics of an optically accessible single-cylinder engine. The engine has a pent-roof shaped combustion chamber with two intake and two exhaust valves. The primary engine variable examined was the intake-flow configuration which was varied by means of shrouded valves. The measured local heat-flux histories on the combustion side of the head were found to have significant cycle-to-cycle and spatial variations, which are believed to be caused primarily by corresponding variations in combustion. The introduction of swirl or tumbling motion to the intake charge accelerated early flame development and increased peak combustion rate. These augmentations consequently caused higher local surface temperatures and increased steady-state as well as local peak heat fluxes.

INCREASING APPLICATIONS of detailed thermostructural and engine-cooling analyses and of detailed engine-cycle analyses during the design of modern spark-ignition (SI) engines have created a strong need for detailed information on the in-cylinder heat-transfer process.

This paper presents the results from the first phase of a continuing comprehensive research program whose objective is to develop analytical heat-transfer models which account properly for the dominant in-cylinder physical processes in SI engines and to evaluate these models experimentally.

The objective of the present study was to investigate experimentally combustion and heat-transfer characteristics of a single-cylinder engine featuring a fast-burn combustion-chamber with optical access. In particular, the effects of intake-flow configuration on combustion and on heat transfer to the combustion-chamber surface were examined by means of heat-release analysis, high-speed flame photography and local time-resolved heat-flux measurements.

Surface heat-flux measurements have been performed by several investigators [1, 2, 3, 4, 5, 6, 7 and 8].* Most of these studies provided experimental data on the effects of engine operational parameters (speed, volumetric efficiency, equivalence ratio, and spark timing) on local surface heat-flux histories. The most comprehensive study of SI engine heat transfer was made by Gilaber and Pinchon [8], who performed surface heat-flux measurements, turbulence and large-scale-velocity measurements, heat-release analysis and multidimensional modeling to study in-cylinder heat-transfer. This study, as well as the previous studies by Alkidas [3,4], were made on engines with pancake-shaped combustion chambers.

In the present study the engine had a fast-burn (pent-roof shaped) combustion-chamber geometry with two intake and two exhaust valves. The principal engine variable examined was intake-flow configuration which was altered by using either one intake valve with-or-without a shroud or both intake valves without any shrouds. The effects of intake-flow configuration on the surface heat transfer have also been studied by Gilaber and Pinchon [8] in a SI engine and by Van Gerpen et al. [9] in a diesel engine.