This content is not included in your SAE MOBILUS subscription, or you are not logged in.
A New Methodology for Comparing Knock Mitigation Strategies and Their Stability Margin
ISSN: 0148-7191, e-ISSN: 2688-3627
Published April 11, 2023 by SAE International in United States
Annotation ability available
The automotive sector is rapidly transitioning to decarbonized, electric vehicles solutions. However, due to challenges with such rapid adoption, Internal combustion engines (ICE) are expected to be used for decades to come. In this transition period it is important to continue to improve ICE efficiency. A key design parameter to increase ICE efficiency is the compression ratio. For gasoline engines, the compression ratio is limited so as to avoid knock. Engine designers can employ several strategies to mitigate knock and enable higher compression ratios. In this study, a new methodology has been developed to compare various knock mitigation strategies. By comparing the knock limited load at a given combustion phasing the expected compression ratio increase can be inferred. Knock mitigation techniques examined in the paper include coolant temperature, manifold temperature, start of injection, split fuel injection, exhaust gas recirculation (EGR), and water injection, both port and direct. Critically, a knock mitigation technology should not excessively compromise the combustion stability. This methodology includes a test for the combustion phasing at a 5% coefficient of variation (CoV) of the net indicated mean effective pressure (nIMEP). The difference between the CA50 at the knock limited load and the stability limited is noted as the stability margin. It is critical for designers and engineers to insure that an engine operates within both the knock and stability boundaries. Different strategies for knock mitigation affect knock and stability differently. The proposed methodology provides an efficient yet accurate way to quantify the impact of technologies. For example, EGR provides a significant increase in knock limited load but also decreases the stability margin by increasing ignition requirements. Water injection, on a per volume basis, provided a smaller increase in knock limited load but has a smaller impact on combustion stability.
CitationMitchell, R., Conway, G., and Wang, Y., "A New Methodology for Comparing Knock Mitigation Strategies and Their Stability Margin," SAE Technical Paper 2023-01-0248, 2023, https://doi.org/10.4271/2023-01-0248.
- Anderson , W. , Yang , J. , Brehob , D.D. , Vallance , J.K. et al. Understanding the Thermodynamics of direct injection spark ignition (DISI) combustion systems: An analytical and experimental investigaton SAE Technical Paper 962018 1996 https://doi.org/10.4271/962018
- Stein , R.A. , Polovina , D. , Roth , K. , Foster , M. et al. Effect of Heat of Vaporization, Chemical Octane, and Sensitivity on Knock Limit for Ethanol - Gasoline Blends SAE Int. J. Fuels Lubr. 5 2 2012 823 843 https://doi.org/10.4271/2012-01-1277
- Imaoka , Y. A study of a Multistage Injection Mechanism for Improving the Combustion of Direct-Injection Gasoline Engines SAE Int. J. Engines 8 3 2015 1080 1087 https://doi.org/10.4271/2015-01-0883
- Cordier , M. , Lecompte , M. , Malbec , L.-M. , Reveille , B. et al. Water Injection to Improve Direct Injection Spark Ignition Engine Efficiency SAE Technical Paper 2019-01-1139 2019 https://doi.org/10.4271/2019-01-1139
- Hoppe , F. , Thewes , M. , Seibel , J. , Balazs , A. et al. Evaluation of the Potential of Water Injection for Gasoline Engines SAE Int. J. Engines 10 5 2017 2500 2512 https://doi.org/10.4271/2017-24-0149
- Breda , S. , Berni , F. , d'Adama , A. , Testa , F. et al. Effects of Knock Intensity and Specific Fuel Consumption of Port Water/Methanol Injection in a Turbocharged GDI Engine: Comparaitive Analysis Energy Procedia 82 2015 96 102
- Potteau , S. , Lutz , P. , Leroux , S. , Moroz , S. et al. Cooled EGR for a Turbo SI Engine to Reduce Knocking and Fuel Consumption SAE Technical Paper 2007-01-3978 2007 https://doi.org/10.4271/2007-01-3978
- Alger , T. Synergies between High EGR Operation and GDI SYSTEMS SAE Int. J. Engines 1 1 2009 101 114 https://doi.org/10.4271/2008-01-0134
- Cairns , A. , Blaxill , H. , and Irlam , G. Exhaust Gas Recirculation for Improved Part and Full Load Fuel Economy in a Turbocharged Gasoline Engine SAE Technical Paper 2006-01-0047 2006 https://doi. org/10.4271/2006-01-0047
- Fabio , B. , Vincenzo , D.B. , and Luigi , T. EGR Systems Employment to Reduce the Fuel Consumption of a Downsized Turbocharged Engine at High-Load Operations Energy Procedia 81 2015 866 873 10.1016/j.egypro.2015.12.134
- Potteau , S. , Lutz , P. , and Leroux , S. Cooled EGR for a Turbo SI Engine to Reduce Knocking and Fuel Consumption SAE Technical Paper 2007-01-3978 2007 https://doi. org/10.4271/2007-01-3978
- Clerk , S.D. Cylinder Actions in Gas and Gasoline Engines Gas-Engine Cylinder Actions Semi-Annual Meeting Paper , 210043 33 92 1921