Abstract
The effects of an electric supercharger (eS) and a dual-loop exhaust gas recirculation (EGR) system on a passenger car’s diesel engine’s emissions and fuel efficiency under various worldwide harmonized light-duty vehicles test procedure (WLTP) reference operation points were investigated using a one-dimensional engine cycle simulation, called GT-Power. After heavy EGR application, the in-cylinder pressure and temperature declined due to a dilution effect. As eS power and rpm increased, the brake-specific fuel consumption (BSFC) decreased because the effects of the air flow rate increased. However, it was unavoidable that nitrogen oxide (NOx) emissions also increased due to the higher in-cylinder pressure and temperature. To induce more EGR to the intake system, a dual-loop EGR system was applied with eS at different low-pressure EGR (LP-EGR) fractions (0, 0.25, 0.5, 0.75, and 1.0). Under these conditions, a design of experiment (DoE) procedure was carried out and response surface plots of the BSFC and brake-specific NOx (BSNOx) were prepared. A multi-objective Pareto optimization method was used to improve the trade-off in results between the BSFC and BSNOx. Through optimization, optimal Pareto fronts were obtained, which suggested design parameters for eS power and rpm to control the engine under various LP fraction conditions.
Highlights
As regulations for passenger cars are being strengthened nowadays, conventional passenger cars with gasoline and diesel engines should be improved to provide better fuel efficiency and reduced emissions
Diesel engines have the advantage of better fuel efficiency to meet such CO2 emission regulations; given their compression ignition (CI) combustion characteristics, emissions of dangerous materials, such as nitrogen oxide (NOx ) and particulate matter (PM), are inevitable
exhaust gas recirculation (EGR) rate, maximum in-cylinder pressure (Pmax), brake-specific fuel consumption (BSFC), brakemean mean effective pressure (BMEP), and brake-specific NOx (BSNOx) were compared against experimental results
Summary
As regulations for passenger cars are being strengthened nowadays, conventional passenger cars with gasoline and diesel engines should be improved to provide better fuel efficiency and reduced emissions. Regulations for passenger cars are being strengthened to meet ‘worldwide harmonized light-duty vehicles test procedures’ (WLTP) or ‘real driving emission cycle’ (RDE), which can describe real driving conditions during the test mode [1]. As these regulations are becoming increasingly harsh, further advanced technologies, such as heavy exhaust gas recirculation (EGR), dual-loop EGR, and two-stage turbocharging with. To reduce the major emissions of CI engines, such as NOx and PM, many after-treatment systems have been applied to passenger car diesel engines Such after-treatment systems are expensive, so reducing emissions by other mechanisms, such as with low-temperature combustion (LTC), should be investigated. A well-controlled LTC engine can improve fuel efficiency and reduce NOx and PM emissions without an after-treatment system
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