Constant Gas/Fuel Ratio with Heterogeneous EGR Reduces Peak Rate of Pressure Rise: Charging exhaust gas into the cylinder using exhaust gas blowdown pressure has been demonstrated to operate a gasoline engine on PCI combustion in the past. The system is called “blowdown supercharging.” Exhaust manifolds are modified to trap high exhaust blowdown pressure. By use of a variable exhaust valve feature, exhaust gas at high pressure is recharged into the cylinder during the early compression stroke to boost cylinder gas pressure. Thus, recharging exhaust gas into the cylinder not only raises the cylinder pressure during the early compression stroke, but also supplies a large amount of EGR gas to the cylinder. Researchers at Chiba University, Hatamura Engine Research, CD Adapco, and Honda R&D, continue their investigation into the combustion system to expand the engine operating range of PCI combustion toward higher torque. Their approach is to refine combustion for a reduced rate of pressure rise so that engine operation is not limited by excessively high cylinder pressure rise.