Investigation into the Application of Turbo-compounding for Downsized Gasoline engines

  • Pengfei Lu

Student thesis: Doctoral ThesisPhD


This thesis sets out to evaluate six novel arrangements of internal combustion engine air path designed to improve the degree of exhaust energy recovery from a practical passenger car engine system. The study was conducted using 1D engine simulation based on two experimentally validated models of modern turbocharged spark ignition engines. Improvements of up to 5% in fuel efficiency are presented, along with reductions of up to 30% in the torque rise time are presented. For at least 7 decades, efforts have been made to recover waste energy from the internal combustion engine. Heat engines, governed by the second law of thermodynamics, inevitably reject a significant proportion of the fuel energy as heat to the environment. Technologies, such as turbo-compounding, (organic) Rankine cycle and thermoelectric generators have been proven effective for waste energy recovery in high load applications. Inverted Brayton cycle is also under investigation currently due to the high exergy availability in exhaust stream and the potential to enhance the overall performance of vehicle engines. However, none of these technologies has been given extensive application in the field of automobiles, especially passenger cars, despite their effectiveness in reducing fuel consumption and CO2 emission. This thesis reviews current and previous studies to summarise the advantages and disadvantages of these technologies as well as the factors that constrain them from wide application. Transient performance, which is rarely considered in the literature, is considered here to allow a more realistic assessment of the technologies merits. Among these approaches, turbo-compounding has the advantage of compact volume, lower complexity and application cost, and is now employed to recover waste heat in heavy duty vehicles, such as mining equipment and road haulage. This thesis reviews the most recent research on turbo-compounding to identify the variables that make the greatest difference to the engine performance. The potential for the augmentation of the fuel economy and power output by a novel implementation of turbo-compounding in light duty vehicles has been demonstrated. The concept of a variable ratio supercharger drive has been studied as part of a novel boosting system to improve the low-speed torque output by up to 55% and overall fuel economy by 3%. After a careful optimisation of the specifications of the variable ratio unit, it is combined with a turbo-compounding system to fully overcome the inherent drawbacks of turboii compounding, namely the tendency to reduce the power output and engine efficiency at low speed. Finally, the concept of divided exhaust period has been introduced in a novel turbocompounded arrangement to regulate the exhaust flow for a better gas exchange process and improve fuel consumption by up to 5% while improving transient response times by 30%.
Date of Award1 Jun 2017
Original languageEnglish
Awarding Institution
  • University of Bath
SupervisorChris Brace (Supervisor) & Sam Akehurst (Supervisor)

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