Comparison of 1-D Modelling Approaches for Wankel Engine Performance Simulation and Initial Study of the Direct Injection Limitations

Paper #:
  • 2018-01-1452

  • 2018-04-03
Recent interest in the possible use of Wankel engines as range extenders for electric vehicles has prompted renewed investigations into the concept. While not presently used in the automotive industry, the type is well established in the unmanned aerial vehicles industry, and several innovative approaches to sealing and cooling have recently been developed which may result in improved performance for ground vehicle applications. One such UAV engine is the 225CS, a 225 cc/chamber single-rotor engine manufactured by Advanced Innovative Engineering (UK) Ltd. This has a water-cooled housing but a novel form of sealed air-cooled rotor which reduces side-seal blowby. To be able to analyse the parameters, opportunities and limitations of this type of engine a model was created in the new dedicated Wankel modelling environment of AVL BOOST. For comparison a second model was created using the established method of modelling Wankel engines by specifying an ‘equivalent’ 3-cylinder 4-stroke reciprocating engine. The output from both of these models was evaluated using engine test data supplied by Advanced Innovative Engineering (UK) Ltd. The model created in the dedicated Wankel environment was found to fit the experimental data more closely. The second part of this investigation was focused on whether the improvements in performance and fuel economy experienced in reciprocating engines as a result of applying direct injection might be applied more simply to a Wankel rotary engine. This potential is because the nozzle can be situated in the cold side of the trochoid housing, taking advantage of both the longer intake phase of the Wankel in turn permitting lower delivery pressures (the intake ‘stroke’ having 270 degrees of eccentric shaft rotation versus 180 degrees for the reciprocating engine), and the fact that the injector can be shielded from combustion pressure and hot burned gases. As it was found to be more accurate, the dedicated Wankel model was used to analyse the interrelationships between injector position, injection pressure and engine speed. Although a number of assumptions were required, and these will affect the accuracy of the model, the results provide a reasonable preliminary assessment of the feasibility of applying direct injection to the 225CS engine. A notable finding was that injection pressures of only 4.5 bar would be sufficient to supply fuel at all engine speeds and that the optimum position for the injector (for maximum fuel injection) was at 597 degrees of eccentric shaft rotation after top dead centre firing.
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