Direct Injection Engine
What it is: Direct Injection (DI) refers to fuel injected directly into the combustion chamber above the piston. Direct Injection has long been used on large diesel engines. Smaller diesels are increasingly adopting direct injection (vs. indirect injection into a pre-chamber). Direct Injection also can be used in spark ignition (generally gasoline) engines instead of port fuel injection- for improved fuel economy, increased full throttle torque and power and potentially for better fuel economy with lean-burn operation.
Ref-Port Fuel Injection (PFI): By comparison, Port Fuel Injection (used spark-ignition engines) have injectors in the intake port near the valve. During the intake stroke, fuel sprayed into the port enters the combustion chamber along with the air charge.
Direct Injection: With Direct Injection Spark Ignition (DISI) engines, 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.
Customer benefit: Better fuel efficiency, improved driveability and more power.
Ford status: Under development.
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