A Comparison of the Effects of Additives on Spark Ignited Combustion in a Laminar Flow System and in an Engine Under Cold-Start Conditions

Experiments have been conducted in a laminar flow system and in a research engine to investigate the effect of additives on the combustion of gasoline-like fuels. The purpose of the laminar system is to enable rapid screening of additives to determine which, if any, have an enhancing effect on the early stages of combustion, especially under conditions of poor fuel vaporization which exist during cold-start in a spark ignited engine and which make flame propagation difficult to start and sustain. The base fuel used in the laminar and engine systems was a 9 component mixture formulated to simulate those components of gasoline expected to be present in the vapor phase in the intake system of an engine under cold-start conditions. In the laminar system, the pre-mixed, pre-vaporized fuel-air mixture is ignited and a time history of the combustion generated, hydroxyl radical chemiluminescence is recorded. Data were collected and analyzed for at least 30 ignition events for three fuel mixtures in a semi-automated process. In experiments with the base fuel, the laminar apparatus was shown to be capable of resolving equivalence ratio differences of 0.01 as a result of the chemiluminescence emission variation with equivalence ratio. In experiments with the base fuel and base fuel-additive mixtures, enhanced chemiluminescence from a mixture containing an additive is considered a predictor of enhanced cold-start performance in the engine. To test this prediction, tests were then made in a DaimlerChrysler V-6 engine modified for single cylinder operation. In each engine test, instrumentation allows measurement and recording of various temperatures, cylinder pressure, crank angle position, and exhaust unburned hydrocarbons for the first 200 cycles of operation. Ten such tests for each fuel were performed. By comparing performance results from tests with and without the additive in the fuel, its effects on the combustion process and on cyclic variability are determined.