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Research of Fuel Components to Expand Lean-Limit in Super Lean Burn Condition (Part II)
ISSN: 0148-7191, e-ISSN: 2688-3627
To be published on September 15, 2020 by SAE International in United States
There is an urgent need to reduce CO2 emissions from the transportation sector. Equipped with an internal combustion engine (ICE) with dramatically improved thermal efficiency, a hybrid electric vehicle would generate roughly the same lifecycle CO2 emissions as a battery electric vehicle. Hence, boosting the thermal efficiency of ICEs could do much to reduce CO2. The right combination of engine technology and fuel technology could greatly improve thermal efficiency and unlock the full potential of the ICE. Thermal efficiency can be improved with a super lean burn. In a super lean burn engine, combustion takes place at lower temperatures. Energy losses are reduced, resulting in major gains in thermal efficiency. As the air-fuel mixture gets leaner, however, a limit is reached at which combustion becomes unstable and misfiring occurs (the "lean limit"). Progress has been made in extending the lean limit via engine technology that enhances ignition and in-cylinder flow. Researchers are also working on new fuels that help extend the lean limit. In Part I (presented at PF&L 2019), we studied the effects of various fuels on the lean limit in super lean burn conditions. We found that the lean limit could be greatly extended and thermal efficiency improved by using the right combination of engine technology and fuel technology. Moreover, we found that the lean limit correlates closely with the duration from start-of-spark to CA10, and that substances which shorten this duration extend the lean limit. In this study, we evaluated the effects of hydrocarbons closer in composition to today's gasoline on the lean limit. The results show that with careful blending, the lean limit can be extended much further than is possible with gasoline. In addition, we looked at autoignition and minimum ignition energy (MIE) to study the lean limit extension mechanism.