Impact of low NOx strategies on holistic emission reduction from a CI engine over transient conditions

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.