Waste Heat Recovery for Heavy-Duty Diesel Engines: A Review of Mechanical Turbocompounding

Heat rejected with the exhaust gas, EGR, engine coolant and other engine components is a major source of efficiency loss in internal combustion engines. One important technology to recover some of this “wasted” heat is turbocompounding. The US Environmental Protection Agency (EPA) estimates that turbocompounding provides a 1.8% efficiency improvement, is already a commercial technology and a penetration rate of 10% is estimated by 2027. Line haul sleeper cab applications are the most likely to see the highest market penetration rates. This paper presents an overview of mechanical turbocompounding for heavy-duty truck engines. For these applications, series turbocompounding is the most suitable configuration and a number of applications have used it since the early 1990s. Unlike other WHR technologies, turbocompounding interacts significantly with the engine through a higher exhaust backpressure. EGR makes it more challenging to realize an efficiency benefit from turbocompounding. It also makes emission control using aftertreatment technology more challenging due to a lower exhaust temperature.