Investigations into Steady-State and Stop-Start Emissions in a Wankel Rotary Engine with a Novel Rotor Cooling Arrangement

Abstract

The present work investigates a means of controlling engine hydrocarbon startup and shutdown emissions in a Wankel engine which uses a novel rotor cooling method. Mechanically the engine employs a self-pressurizing air-cooled rotor system (SPARCS) configured to provide improved cooling versus a simple air-cooled rotor arrangement. The novelty of the SPARCS system is that it uses the fact that blowby past the sealing grid is inevitable in a Wankel engine as a means of increasing the density of the medium used for cooling the rotor. Unfortunately, the design also means that when the engine is shutdown, due to the overpressure within the engine core and the fact that fuel vapour and lubricating oil are to be found within it, unburned hydrocarbons can leak into the combustion chambers, and thence to the atmosphere via either or both of the intake and exhaust ports. As well as shutdown it also affects the startup process, where higher hydrocarbon emissions are caused due to the forced transfer of the unburned gases to the intake and exhaust ducts as the core depressurizes across the sealing grid when it is stationary. These emissions then sit in those volumes, possibly then escaping to the outside world; clearly this is also very important with respect to the SHED testing of any vehicle the engine might be fitted to.The SPARCS concept is discussed with respect to how it functions versus a conventional wet sump arrangement (as employed by oil cooled rotor Wankel engines). Measurements are taken and steadystate emissions and fuel consumption results with and without pressurization of the core are presented; such a comparison has not been made before. In general, power output, brake specific fuel consumption, hydrocarbon emissions, and combustion efficiency are all better with a depressurized core, with only small improvements in cooling (defined by rotor air inlet temperature) being apparent when it is pressurized. A hypothesis for why this should be so is developed, the knowledge of which can help to guide further development.The reasons for the engine on/off hydrocarbon issue are apparent. Using a solenoid valve as a means of venting the rotor core pressure directly to the engine intake just before shutdown is proposed as a means of alleviating this problem. This approach would feed the hydrocarbon-rich gases from the core through the combustion process and out through the catalytic converter just before the engine is switched off. In automotive applications this engine is to be used as a range extender and hence there is a great degree of control regarding all modes of its operation, including startup and shutdown, which is the approach investigated for mitigation here.The results show that depressurizing the core in this manner results in a maximum reduction in total hydrocarbon emissions during warm shutdown and restart of 80% and 60%, respectively. However, it must be remembered that with the pressure relieved in the core, the cooling capability there is slightly reduced, and so the approach has to be calibrated c...

Testing of a Modern Wankel Rotary Engine - Part III: Firing Condition Analysis

“…In a manner different from what was expected, the pressure did not present fluctuations related to the pressure cycles evolving in the main chambers. The only tangible mechanical effect (neglecting here the effects on the emissions that are covered in [20]) of the firing conditions was increased core pressure with respect to the values recorded in the previous work [2]. Those pressure values are summarised in Table 7 where they are shown to be dependent only on load rather than the engine rotational speed.…”

“…Within the project, much effort was spent on innovative fuel control strategies to reduce the rotary's well-known appetite for fuel [17,18]. In addition, the several theoretical investigations supported by numerical activities proved that is possible to improve the emissions of Wankel rotary engines and successfully employ them as range extenders [19,20]. Furthermore, the Wankel configuration demonstrated the capability to be coupled with a rotary expander of the same geometric family and so improve the overall system efficiency and fuel consumption while further reducing its emissions [21].…”

Testing of a Modern Wankel Rotary Engine - Part II: Motoring Analysis

“…The Institute for Advanced Automotive Propulsion Systems (IAAPS) at the University of Bath carried out the testing and performance development of the AIE 225CS rotary engine by means of experimental and numerical activities, with the primary objective of making the thermal machine Euro 6 compliant. In that respect, many development aspects have been analysed and tested within a prolific partnership between the academic research team and AIE UK, ending up in interesting works on fuel control strategies specifically designed for rotary engines [4] [5] and theoretical and numerical investigations aimed at improving the emissions by means of novel mechanical configurations [6] [7]. Furthermore, AIE UK designed a specific rotary expander to be employed in series with the conventional Wankel engine in order to improve the overall efficiency of the system.…”

Testing of a Modern Wankel Rotary Engine - Part IV: Overall Mechanical and Thermal Balance

“…The University of Bath and the IAAPS research group, as the academic partner of the ADAPT-IPT project, tested the AIE 225CS 10/19/2016 engine at their laboratories. The experimental testing was carried out mainly at steady-state conditions with some additional investigations on the emissions during the engine start and stop, as also reported in [11,12,16].…”

“…The engine was tested in steady-state motoring and firing conditions [11][12] using a bespoke experimental plan, data acquisition system and combustion analyser [13]. Subsequently, given the flexibility of the GEMS electronic control unit employed, specific engine control strategies were developed and implemented to reduce both the fuel consumption and emissions of the engine [14,15] assessing those parameters at steady-state operating conditions and during the start and stop of the engine [16]. Finally, unusual porting configurations for emissions reduction and the application of a rotary expander connected as an energy recovery system were evaluated by means of numerical and experimental activities, respectively [17,18].…”