Performance Characteristics Analysis of Variable Expansion Ratio Expander Based on Organic Rankine Cycle for Automobile Waste Heat Recovery

摘要

A reciprocating piston expander model based on organic Rankine cycle (ORC) is built for engine waste heat recovery. The expander characterizes by variable expansion ratio through adjusting working fluid injection timing. This paper investigates the effect of working fluid evaporating pressure, expansion ratio and clearance volume on the expander performance which mainly includes output power, equivalent recovery efficiency, total output power, expander efficiency, and the weighted efficiency of the expander, weighted heat recovery efficiency of the expander. The results demonstrate that the total output power and the equivalent heat recovery efficiency increase with working fluid evaporating pressure under overall operating conditions, while the increment is negligible. The expander reaches maximum total output power up to 83.4kW under c100 engine condition and 1.1MPa working fluid evaporating pressure within the research operating conditions. The peak values of total output power and equivalent recovery efficiency are 19.9kW and 31.2% respectively when the expansion ratio reaches six. The above two indicators reduce with further increasing or decreasing expansion ratio for over expansion or under-expansion respectively. The expander performance deteriorates as clearance volume increase due to the reduction of effective expansion ratio. Generally, the variable expansion ratio expander has an excellent performance in waste heat recovery for the automobile.