DISI: Direct Injection Spark Ignition - fuel is injected in one of two ways, depending on operating conditions. With lean burn operation (at low to mid loads), the engine is run unthrottled (similar to diesel) with fuel injected after the air has entered, causing a higher fuel concentration near the spark plug for easy ignition. This is known as the stratified charge mode. The overall air/fuel ratio is lean for better fuel consumption. At mid to high engine loads, fuel is injected during the air intake stroke to promote good mixing. This process is known as the homogenous mode of operation. Fuel injected and evaporating directly in the combustion chamber cools the air slightly for higher volumetric efficiency and power. It also allows a slightly higher compression ratio for improved fuel efficiency. Since all fuel being injected goes directly into the cylinder, it can be metered more precisely, promoting improved transient control for reduced engine-out emissions.