Abstract
The article compares the accuracy of different exhaust gas recirculation (EGR) correction factor models under engine conditions. The effect of EGR on the laminar burning velocity of a EURO VI E10 specification gasoline (10% Ethanol content by volume) has been back calculated from engine pressure trace data, using the Leeds University Spark Ignition Engine Data Analysis (LUSIEDA) reverse thermodynamic code. The engine pressure data ranges from 5% to 25% EGR (by mass) with the running conditions, such as spark advance and pressure at intake valve closure, changed to maintain a constant engine load of 0.79 MPa gross mean effective pressure (GMEP). Based on the experimental data, a correlation is suggested on how the laminar burning velocity reduces with increasing EGR mass fraction. This correlation, together with existing models, was then implemented into the quasi-dimensional Leeds University Spark Ignition Engine (LUSIE) predictive engine code and resulting predictions are compared against measurements. It was found that the new correlation is in good agreement with experimental data for a diluent range of 5%-25%, providing the best fit for both engine loads investigated, whereas existing models tend to overpredict the reduction of burning velocity due to EGR.
Highlights
Government legislation on controlling emissions from combustion engine powered vehicles is becoming ever more stringent
We show that while all models provide reasonably good agreement with experimental data at low levels of exhaust gas recirculation (EGR) (5%-10%), only the new found correction factor can match the measured pressure traces and mass fraction burned at higher levels of EGR (20%25%) as existing models overestimate the reduction in laminar burning velocity due to the effects of EGR to varying degree
The correction factor should account for the impact of EGR on steady-state flame development, whereas the impact on early flame development is modelled by the time taken to form the flame kernel
Summary
Government legislation on controlling emissions from combustion engine powered vehicles is becoming ever more stringent. Car manufacturers have to keep improving their engines to minimise fuel consumption and emissions. An effective strategy to reduce NOx emissions is to use Exhaust Gas Recirculation (EGR), that is, to recirculate cooled exhaust gas into the cylinder. High levels of EGR have been found to reduce NOx emissions but carbon monoxide (CO), particulate mass (PM) and particulate number (PN) [1, 2, 3]. EGR has been found to reduce the chances of auto-ignition due to lower end gas temperatures [4, 5, 6, 7, 8]. The reduction in end gas temperature allows the compression ratio to be increased, leading to improved engine efficiency [9]
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