The Impact of Fuel Composition on the Combustion and Emissions of a Prototype Lean-Boosted PFI Engine 2010-01-2094
Toyota and BP have performed a collaborative study to understand the impact of fuel composition on the combustion and emissions of a prototype 1.8L lean boosted engine.
The fuel matrix was designed to understand better the impact of a range of fuel properties on fundamental combustion characteristics including thermal efficiency, combustion duration, exhaust emissions and extension of lean limit. Most of the fuels in the test matrix were in the RON range of 96 - 102, although ethanol and other high octane components were used in some fuels to increase RON to the range 104 - 108. The oxygen content ranged from 2 - 28%, and constituents included biocomponents, combustion improving additives and novel blend components.
Performance and emissions tests were conducted over a range of engine operating conditions. Thermal efficiency was mapped at stoichiometric and lean conditions, and the limit of lean combustion was established for different fuels.
Peak thermal efficiency, which was largely governed by resistance to auto-ignition, was found to be primarily described by fuel RON.
The presence of fuel borne nitrogen was shown to increase NOx emission dramatically, this was particularly apparent when operating under lean conditions, where low combustion temperatures would otherwise result in very low NOx emissions.
Although the ignition improving additives demonstrated limited impact on the combustion characteristics of the engine, bulk changes in fuel chemistry were shown to significantly decrease the combustion duration and in so doing significantly extended lean-limit of operation.
This paper details the engine, test fuels and experimental methods, explores the findings of this research and provides a hypothesis to explain each effect.