Adaptive control of secondary air injection to the thermal reactor of a turbocharged S1 engine

Jasper, Brian Colin (1980) Adaptive control of secondary air injection to the thermal reactor of a turbocharged S1 engine. University of Southampton, Doctoral Thesis.

Abstract

This thesis examines the feasibility of using an adaptive method of controlling secondary air flow to a thermal reactor mounted in the exhaust stream of a turbocharged SI engine. The original theory behind the thermal reactor concept was to operate an engine at very rich mixtures so that formation of NOx emission, would be limited by the combustion inhibiting nature of the unburnt fuel. The remaining fuel, which is essentially CO, H2 and HC, is then mixed with air at near atmospheric pressure and is burnt off in a reaction vessel mounted In the exhaust stream. The major disadvantages of this method of emissions control is that there is a loss in fuel economy and the location of the reaction vessel in the exhaust causes the engine back pressure to rise, which consequently lowers the volumetric efficiency of the engine. These disadvantages can be minimised if a turbocharger is placed downstream of the reactor so that use can be made of the waste energy that is liberated by the secondary combustion. This is then converted to boost pressure by the compressor and used to improve the air flow through the engine. By suitable selection of the fueling characteristic, the engine can be made to operate nearer stoichiometric air/fuel ratios at higher mass flows, which will limit the amount of secondary combustion and hence constrain maximum combustion temperatures and torque developement to safe levels. A computer model was developed to simulate the steady state combustion process and from this it was possible to gain an understanding of combustion behaviour at different locations In the reactor. It also enabled temperature predictions to be made from a knowledge of input emissions. Using reactor gas temperatures as an Indication of performance, fixed and variable step type controllers were tried which were based on the gradient estimate method. Control of secondary air using these methods was shown to be feasible and a collection of test results is presented, demonstrating the performance of each type of controller.

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