This design study consisted of 108 datasets in total, consisting of a combination of 12 piston shapes, 3 applied spray injection timings, and 3 applied swirl ratios. The 3 spray injections (referred here as SOI (start of injection)) consisted of -10.2, -8.5, and -6.2 degrees before top dead center of the power stroke. The swirl ratio is a dimensionless quantity defined as the ratio of angular speed of the fluid relative to the engine speed, and is used to quantify the rotation motion of the flow inside of the cylinder. The geometric variations consisted of 12 variation of the bowl shape. There is a variation in the piston bowl shape which affects the fuel spray - bowl interaction and hence the air-fuel mixing (or equivalence ratio distribution) inside the cylinder. We can use the different dimensions of the piston bowl (Dmin, Dmax, Hmin, Hmax, R, Dcrown, Hcrown) to understand the pattern of geometry change. Improvement in air-fuel mixing and equivalence ratio distribution results in to improvement in power output.