For years, engineers have known that if they could build a petrol engine that worked like a diesel engine-in other words, one in which fuel is injected directly into the cylinder and the stratified, rich mixture right near the spark plug is ignited-they would have an engine that achieved both the fuel efficiency of a diesel engine and attained the high output of a conventional petrol engine. However, development of such an engine has been impeded by petrol's poor combustibility. Diesel engines operate on a thermodynamic cycle, meaning that as long as a sufficient temperature is reached, thorough ignition will occur regardless of the air/fuel mixture condition. In order to achieve combustion with petrol, gaseous fuel and air must be mixed to form just the right air/fuel mixture, and precise control of position and timing of the air/fuel mixture is necessary to ensure delivery of this mixture to the very limited space between the spark plug electrodes in the very specific timing of ignition. The GDI engine is able to achieve this through Mitsubishi's technology that enables precise control over the air/fuel mixture. 1. Key Concepts (1) Two Combustion Modes In response to driving conditions, the GDI engine changes the timing of the fuel spray injection, alternating between two distinctive combustion modes- stratified charge (Ultra-Lean combustion), and homogenous charge (Superior Output combustion). Under normal driving conditions, when speed is stable and there is no need for sudden acceleration, the GDI engine operates in Ultra-Lean Mode. A spray of fuel is injected over the piston crown during the latter stages of the compression stroke, resulting in a optimally stratified air/fuel mixture immediately beneath the spark plug. This mode thus facilitates lean combustion and a level of fuel efficiency comparable to that of a diesel engine. The GDI engine switches automatically to Superior Output Mode when the driver accelerates, indicating a need for greater power. Fuel is injected into the cylinder during the piston's intake stroke, where it mixes with air to form a homogenous mixture. The homogenous mixture is similar to that of a conventional MPI engine, but by utilising the unique features of the GDI, an even higher level of power than conventional petrol engines can be achieved.