Engine Tests Demonstrate Increased Power Output with Higher Compression Ratio: Engineers at Yanmar and researchers at Shiga Prefecture University modified a 3.3-liter four-cylinder natural gas engine to operate on premix compression ignition (PCI) combustion in a multi-cylinder engine and investigated engine performance and variability of combustion among the cylinders. To expand the range of engine operation on PCI combustion, researchers increased the effective compression ratio and controlled intake charge temperature so that the engine could produce high indicated thermal efficiency and low NOx emissions. With a higher compression ratio, it is possible to operate the engine at a higher excess ratio and the cylinder-to-cylinder variability becomes low. At the same level of variability, a higher compression ratio increases engine power output.