Abstract
Research and /or Engineering Questions/Objective: The use of light alcohols in spark-ignition engines is an interesting option to secure domestic energy supply and decarbonize transport. The impact of these fuels on engine control strategies can be explored at low cost using engine cycle simulations. Existing models, however, insufficiently account for the specific effects of alcohols on engine operation. The goal of the current work is thus to develop an engine cycle code that can accurately predict performance, efficiency, pollutant emission and knock onset in state-of-the-art neat alcohol engines.
Methodology – Quasi-dimensional engine modeling is put forward as a useful tool for cheap and fast optimization of engines. This model class derives the mass burning rate of fuel from turbulent combustion models. Previous work by the authors focused on obtaining reliable data for the laminar burning velocity of methanol and ethanol. This is a fundamental building block of any turbulent combustion model and groups the chemical effects of pressure, temperature, equivalence ratio and residual gas on combustion. Now, this data is implemented in an engine code and used to reproduce the experimental cylinder pressure traces obtained on three different flex-fuel engines. Additionally, these traces are used to compare various turbulent combustion models.
Results – Comparison of experimental and simulated cylinder pressure traces confirmed the predictive power of the developed engine cycle model. A wide variety of engine operating points on both methanol and ethanol were accurately reproduced thanks to the new laminar burning velocity data. Turbulent combustion models accounting for thermo-diffusive properties were shown to hold a slight edge over simpler formulations.
Limitations of this study – An important limitation of the current study is the absence of accurate estimations for the in-cylinder bulk flow and turbulence. Also, the current model is only validated for port-fuel injected engines. Further work will focus on the effects of direct injection and look at pollutant formation.
What does the paper offer that is new in the field in comparison to other works of the author – Compared to previous work the effects of in-cylinder pressure, temperature and mixture composition on the combustion are more accurately predicted thanks to the inclusion of new and widely validated laminar burning velocity data. In contrast to other studies, the current experimental database also includes measurements for a wide range of equivalence ratios and elevated amounts of exhaust gas recirculation.
Conclusion – The current work focused on adapting the various submodels of quasi-dimensional engine codes to the properties of light alcohols. The developed simulation tools can be used with confidence to optimize current and future engines running on neat methanol and ethanol.
KEYWORDS – Methanol, Ethanol, Spark Ignition Engine, Thermodynamic, Modeling