Fuel injectors come in various types and can be classified according to various standards such as structure, number of nozzles, and electromagnetic coil resistance. Common classifications also include those based on installation location and control method. Based on installation location, they can be divided into direct injection and external injection. Direct injection injects fuel directly into the combustion chamber at high pressure (up to 500 bar for gasoline engines and 2500 bar for diesel engines), contributing to higher air-fuel mixture efficiency. However, it requires high-quality fuel and is prone to carbon buildup on intake valves. External injection includes multi-point injection in the intake manifold and single-point injection in the intake pipe. It has lower injection pressure (approximately 0.3-0.5 MPa), a relatively simple structure, low maintenance costs, less stringent fuel requirements, and the fuel has a flushing effect on the intake manifold, resulting in a relatively lower risk of carbon buildup.
Based on structure, they can be divided into orifice type, needle type, and plate valve type. Orifice injectors have multiple small-diameter nozzles, high pressure, and good atomization, and are mostly used in direct injection combustion chambers; needle-type injectors have a needle shaft, annular nozzles, strong self-cleaning ability, and resistance to carbon buildup; plate valve injectors have a wide dynamic flow range and strong anti-clogging ability. According to the control method, they can be divided into mechanical control type and electronic control type. Mechanical control type has a reliable structure but lower precision; electronic control type is controlled by ECU, has fast response, and supports multiple injections.