Combined Effects of Valve Strategies, Compression Ratio, Water Injection and Cooled EGR on the Fuel Consumption of a Small Turbocharged VVA Spark-Ignition Engine

Paper #:
  • 2018-01-0854

  • 2018-04-03
In this work, various techniques are numerically investigated in order to assess and quantify their relative effectiveness in reducing the Brake Specific Fuel Consumption (BSFC) of a downsized turbocharged spark-ignition VVA engine. Analyzed solutions include the variable compression ratio, the port Water Injection (WI), and the external cooled EGR. The numerical analysis is developed in a 1D modeling framework. The examined engine is schematized in GT-Power™ environment, employing refined sub-models for an accurate description of in-cylinder processes, such as turbulence, combustion, knock, and heat transfer. In particular, the utilized combustion and knock models have been extensively validated in previous papers, at different speed/load points and intake valve strategies, including operating conditions with a relevant internal EGR rate, and in presence of water injection. The 1D model is coupled to an automatic optimizer, to explore the potential BSFC benefits arising from the adoption of previously listed solutions. The base engine architecture, only including the VVA device, is preliminary optimized to define reference BSFC levels. Then, various solutions are analyzed one by one or combined, to outline the maximum achievable fuel consumption gains. Operating conditions typical of a WLTP driving cycle are considered. More than proposing an advanced, very complex engine architecture, the aim of the activity is to clearly outline isolated and mutual effects of each technique by varying the operating point. In this way, some guidelines can be offered to engine developers to select the preferred solution, and to have information on the expected improvements. Optimization outcomes show that the WI proves a higher effectiveness at medium-high load, mainly thanks to its knock suppression capability, while cooled EGR is preferable at low load, to reduce the pumping work. If coupled to the WI, adopting a high CR is always beneficial. Combining the above techniques provides BSFC reductions of 6.9%, 5.2% and 9.0% at low, medium and high load, respectively.
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