An LPG engine for heavy duty vehicles has been developed using liquid phase LPG injection (hereafter LPLI) system, which has regarded as as one of next generation LPG fuel supply systems.
In this work the optimized piston cavities were investigated and chosen for an LPLI engine system. While the mass production of piston cavities is considered, three piston cavities were tested: Dog-dish type, bathtub type and top-land-cut bathtub type. From the experiments the bathtub type showed the extension of lean limit while achieving the stable combustion, compared to the dog-dish type at the same injection timing.
Throughout CFD analysis, it was revealed that the extension of lean limit was due to an increase of turbulence intensity by the enlarged crevice area, and the enlargement of flame front surface owing to the shape of the bathtub piston cavity compared to that of the dog-dish type.
For the top-land-cut piston cavity, the tendency for knocking to occur was reduced due to the enlarged clearance height. However, with the bathtub cavity thermal efficiency decreased compared with the dog-dish type, due to an increase of the surface to volume ratio.