Analysis of the Hardware Requirements for a Heavily Downsized Gasoline Engine Capable of Whole Map Lambda 1 Operation

Paper #:
  • 2018-01-0975

  • 2018-04-03
Gasoline engine downsizing is already established as a technology for reducing vehicle CO2 emissions. Further benefits are possible through more aggressive downsizing, however, the trade-off between the CO2 reduction achieved and vehicle drivability limits the level of engine downsizing currently. There have also been long standing legislative limits on the tailpipe hydrocarbon, NOX and particulate emissions. However, until recently these emissions were only measured over prescribed legislative test cycles. With the introduction of real driving emissions (RDE) testing the engine operating region under scrutiny during compliance testing has significantly increased. Furthermore, manufacturers may be required to disclose their engine base emissions strategy (BES) and any auxiliary emissions strategy (AES), which may preclude the use of fuel enrichment for component protection in future engines. MAHLE and Aeristech recently developed a heavily downsized demonstrator engine and vehicle to explore the limits, and potential benefits, offered through engine downsizing. The 1.2 litre, 3-cylinder, MAHLE downsizing engine was re-configured, in conjunction with an Aeristech 48 V electric supercharger (eSupercharger), to enable it to achieve a BMEP level of 35 bar and a specific power output in excess of 160 kW/litre. The eSupercharger enables high specific power output, good low speed torque and excellent transient response. However, at specific power levels much above output levels of 90 kW/litre the engine operates with excess fuel in order to protect the turbine from excessive exhaust gas temperatures. In this analytical study the boosting system requirements to maintain lambda 1 fuelling across the entire engine operating map are investigated. Exhaust gas recirculation (EGR) will be utilised, via a mixed-pressure EGR circuit (pre-turbine supply to mid-pressure on the intake). The paper will focus on defining the boosting and EGR system hardware requirements to achieve the required EGR flow rates whilst maintaining a very high specific power output.
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