Gustav Nyrenstedt, Ph.D. Candidate, Supervised by Professor Bengt Johansson
Modern engines require low emissions and good fuel economy at a low purchase price. Traditionally, there has been a trade-off between good fuel economy and low emissions for heavy-duty engines. This has been compensated for by adding costly after-treatment systems leading to an increased purchase price.
This dissertation covers how modern engines can mitigate the effects of the emissions-fuel economy trade-off by utilizing higher in-cylinder pressures and waste heat recovery systems. One such modern engine concept is the double compression expansion engine which has previously been reported to deliver high brake efficiencies at a number of load conditions. However, reduced heat losses become increasingly important for modern engine concepts due to the recovery of normally wasted exhaust energy.
This dissertation will prove how the usage of multiple injectors is a well-suited strategy to reduce heat losses. CFD simulations showed how two injectors placed at the rim of a flat bowl reduced the heat losses by 4.2 %-points giving a direct efficiency increase of 1.9 %-points. These results were confirmed in research engine experiments. Furthermore, the dissertation will explain how the standard injection system is not suitable for combustion control through multiple injections. This was proven by studying isobaric combustion strategies in an optical engine where high soot levels were experienced. The dissertation ends by providing a production engine concept equipped with multiple injectors for future studies.
Gustav has been a Ph.D. student in Prof. Bengt Johansson's group at KAUST since August 2016. He started his Ph.D. studies right after receiving his Master's degree from Lund University in June 2016. Gustav has received several awards for his presentations such as the Society of Automotive Engineering Excellence in Oral Presentation award in 2019. Furthermore, Gustav was the Vice President of the KAUST Graduate Student Council in 2018 as well as the founder of the KAUST PSE Student Senate in 2020.