Yi Cui

Miller-Cycle Regulatable, Two-Stage Turbocharging System Design for Marine Diesel Engines

The increasingly stringent NOx emission regulations of the International Marine Organization (IMO) have demanded new design concepts and architectures for diesel engines. The Miller cycle, which reduces the in-cylinder combustion temperature by reducing the effective compression ratio, is the principal measure used for reducing NOx specific emissions; however, this is at the cost of volumetric efficiency and engine power. Therefore, it is essential to combine the Miller cycle with a highly boosted turbocharging system, two-stage turbocharging for example, to recover the power. While much work has been done in the development of Miller-cycle regulatable two stage turbocharging system for marine diesel engines, there are nonetheless few, if any, thorough discussions on system optimization and performance comparison. This study presents a theoretical optimization design process for a Miller-cycle regulatable, two-stage turbocharging system for marine diesel engines. First, the different scenarios and regulation methods of two-stage turbocharging systems are compared according to the system efficiency and equivalent turbine flow characteristics. Then, a multizone combustion model based on a one-dimensional cycle simulation model is established and used for the optimization of valve timings according to the IMO NOx emission limits and fuel efficiencies. The high- and low-stage turbochargers are selected by an iterative matching method. Then, the control strategies for the boost air and high-stage turbine bypass valves are also studied. As an example, a Miller-cycle regulatable, two-stage turbocharging system is designed for a highly boosted high-speed marine diesel engine. The results show that NOx emissions can be reduced by 30% and brake specific fuel consumption (BSFC) can also be improved by a moderate Miller cycle combined with regulatable two-stage turbocharging.

Steady-state and transient control strategies for a two-stage turbocharged diesel engine

Two-stage turbocharging technology is widely used to achieve higher engine power density and lower exhaust emissions. To solve a series of contradictions in matching, a regulated two-stage (RTS) turbocharging system is applied to reasonably control boost pressure. This paper investigated steady-state and transient control strategies for an RTS turbocharging system to achieve optimum fuel economy in steady-state conditions and better performance in transient conditions. The economic control strategies for steady-state operational conditions were based on an economic regulation law, which was established by a steady-state test of an engine with an RTS turbocharging system under all operating conditions. To optimize the transient performance, open-loop and closed-loop control systems (the latter with dynamic judgement) for the RTS system were designed and validated with experiments on a heavy-duty diesel engine. The experimental results demonstrated that the open-loop control strategy and the closed-loop strategy with dynamic judgement could improve the transient response performance. The optimum transient response performance was achieved by the closed-loop control system with dynamic judgement. Additionally, the combination of steady-state and transient control strategies could achieve the best fuel economy in steady-state conditions and good transient response performances.

Miller Cycle-Regulatable Two Stage Turbocharging System Design of Marine Diesel Engines

Satisfying the coming International Marine Organization (IMO) NOx emissions requirements and regulations is the main focus of attention in marine engine design. Miller cycle, which reduces in-cylinder combustion temperature by reducing effective compression ratio, is the main measure to reduce NOx specific emissions on the cost of volumetric efficiency and engine power. Therefore, it is essential to combine Miller cycle with highly boosted turbocharging system, for example, two stage turbocharing, to recover the power. In this paper, different two stage turbocharging system scenarios are introduced and compared. The system design and matching process is presented. A multi-zone combustion model based one dimensional cycle simulation model is established. The intake valve closure timing and the intake exhaust valves overlap duration are optimized according to the IMO NOx emission limits by the simulation model. The high and low stage turbochargers are selected by an iterative matching method. Then the control strategies of the boost air and the high stage turbine bypass valves are also studied. As an example, a Miller cycle-regulatable two stage turbocharging system is designed for a type of highly boosted high speed marine diesel engine. The results show that the NOx emissions can be reduced 30% and break specific fuel consumption can also be improved by means of moderate Miller cycle combined with regulatable two stage turbocharing.Copyright