A liquid phase multi-point injection (MPI) fuel system for liquefied petroleum gas (LPG) offers increased volumetric efficiency relative to conventional gaseous phase MPI fuel systems. Because liquid phase systems evaporate the fuel in the inlet port, the air/fuel mixture entering the cylinder is cooler and denser. However, executing a reliable, high-performance liquid phase LPG MPI fuel system presents a number of key challenges. These include: 1. maintaining the LPG in a liquid phase at the fuel rail under all vehicle operating conditions; 2. minimizing heat transfer to the fuel tank to enable fast and repeatable refueling; and 3. achieving acceptable hot start performance with a mono-fuel LPG fuel system. Numerical and statistical methods can be used to help address these challenges. In this paper, an investigation into the thermal behavior of a liquid phase MPI fuel system is presented. The use of statistical response surface modeling, numerical modeling techniques and multi-objective optimization for this purpose is highlighted.
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