Abstract
The use of biofuels to replace fossil fuels as well as more stringent emission regulations for internal combustion engines cause a challenge for the engine manufacturers to build engines that can cope with a wide range of fuels, but still offer low exhaust emissions with no detriment to performance. In this work a test bed with a compression ignition engine has been used to measure emissions when using a ternary fuel blend between diesel, biodiesel and ethanol together with exhuast gas recirculation (EGR) and different fuel delivery techniques. EGR with biofuels have the potential to significantly reduce NOx over conventional diesel combustion. The fuel used, B2E9 achieves a 10% renewable content as set out in the UK government’s Renewable Energy Directive. Most studies reported in the literature evaluates emissions reduction technologies by only changing one factor-at-a-time at steady state conditions. This paper addresses these issues and presents a methodology utilising a Central Composite Design (CCD) analysis to optimise four engine parameters which include EGR percentage, main injection SOI, pilot injection SOI and pilot injection open duration over a transient drive cycle (WLTP) which makes the results more applicable to real world driving conditions. The optimisation of the CCD showed that NOx emissions decreases by 25% when the maximum exhaust gas recirculation is set to 45%, the main injection is retarded by 2 CADs, the pilot injection dwell time is set to 21 CADs and 24% of the fuel is delivered through the pilot injection. CO emissions increase by approximately 47% as a result of the decrease in NOx emissions.
Highlights
The European Union (EU) has implemented emission standards to reduce the environmental impact of road transport
Engine emissions were investigated over the World Harmonised Light vehicle Test Procedure (WLTP) drive cycle
The principal model analysis was based on the analysis of variance (ANOVA) which provided statistical information including the p-values of the different model terms. p-values of less than 0.02 are deemed as highly significant, which means that the probability of this phenomena is due to chance, is less than 2%
Summary
The European Union (EU) has implemented emission standards to reduce the environmental impact of road transport. These measures include the Euro 6 legislation, which enforces limitations on harmful gasses in vehicle exhaust. The exhaust gas increases the heat capacity of the combustion mixture, reducing the combustion temperature.[3,4] The application of EGR (usually \50%) reduces the volumetric efficiency of the engine due to the rise in inlet charge temperature with less dense, hot exhaust gas replacing cool inlet air. The local flame temperature during combustion is reduced, which reduces the formation of NOx gasses.[3,5] Unburned hydrocarbons (UHC) and CO emissions increase with increasing use of University of the West of England, Bristol, UK
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