Fuel consumption and pollutant emissions of spark ignition engines during cold-started drive cycles
This thesis details the development and evaluation of a procedure to predict the fuel consumption and pollutant emissions of spark ignition engines during cold-started drive cycles. Such predictions are of use in the early development and optimisation of an engine and vehicle combination with regard to legislated limits on vehicle performance over defined drive cycles. Although levels of pollutant emissions are the main focus of legislation, reducing fuel consumption is also of interest and drive cycle fuel consumption figures provide a useful benchmark of vehicle performance appraisals. The procedure makes use of a combination of engine friction models and experimentally defined correction functions to enable the application of fully-warm engine test bed data to cold-start conditions. This accounts for the effects of engine temperature on friction levels, mixture preparation and start-up transient behaviour. Experimental data to support the models and assumptions used are presented and discussed. Although not an essential part of the procedure, neural networks have been used to characterise the fully-warm engine mapping data. These are shown to provide an effective way of interpolating between engine mapping points. To facilitate the prediction of tail-pipe emissions, a simple catalyst efficiency model has been included and the complete procedure incorporated into a single software package enabling second-by-second fuel and emissions flow rates to be predicted for a given engine and vehicle combination over a defined drive cycle. This package is called CECSP or the Cold Emissions Cycle Simulation Program. The program has been designed to run on PC machines. The procedure has been validated by application to a typical 1.8 litre medium sized vehicle driven over the ECE+EUDC drive cycle and the predictions found to be within the target accuracy of +/-5% for fuel consumption and +/-10% for engine-out emissions. Envisaged applications of the procedure to rank the sources of increased fuel consumption and emissions due to cold-starting and engine and vehicle details are outlined.