With multiport fuel injection, fuel atomizes as it’s sprayed into the intake port and then is pulled into the combustion chamber. LSPI is an abnormal combustion event caused by higher cylinder pressures common in turbocharged GDI engines running in low-speed, high-torque conditions.
A fuel-pressure regulator maintains a controlled fuel pressure at each injector, or a controlled differential pressure across the injector.Direct-injected engines also are afflicted by a condition called low-speed pre-ignition (LSPI). The gasoline fuel injector is an electromagnetic (solenoid-operated) or mechanical device used to direct delivery of or to meter pressurized fuel, or both. In the typical gasoline fuel-injection system, an electric fuel pump provides a specified fuel flow at the required system pressure to one or more fuel-injection valves, or fuel injectors. When the feedback signal from an exhaust-gas oxygen sensor is included, these systems allow the engine air-fuel ratio to be maintained near the stoichiometric ratio (14.7:1) during normal operating conditions. Many of the systems are of the speed-density type, in which the mass airflow rate is calculated based on cylinder displacement and the measured intake-manifold absolute pressure (engine load), engine speed, intake-manifold air temperature, and theoretical volumetric efficiency. On automotive spark-ignition engines, the carburetor has largely been replaced by a gasoline fuel-injection system with either mechanical or electronic control of fuel metering. See Diesel engine, Internal combustion engine, Mean effective pressure To prevent an unloaded diesel engine from increasing in speed until it destroys itself, a governor is required to limit maximum engine speed. The mean effective pressure developed by combustion is controlled by the volumetric capacity of the injection pump. The intake air is not throttled in a diesel engine, with load and speed control accomplished solely by controlling the quantity of fuel injected. A timing device in the injection pump automatically advances the start of fuel delivery as engine speed increases to optimize the start of combustion. Extremely accurate fuel metering is necessary, with the start of injection occurring within a precision of up to 1° of engine crankshaft angle. The high pressure is necessary to deliver fuel against the highly compressed air in the engine cylinders at the end of the compression stroke, and to break up the fuel oil which has low volatility and is often viscous.
2 (100 MPa) or higher for direct-injection engines. 2 (10–35 megapascals) for indirect-injection engines, and up to 15,000 lb/in.
The diesel engine must be supplied with fuel from the injection nozzle at a pressure of 1500–5000 lb/in. In the spark-ignition engine, the fuel is injected into the air before it enters the combustion chamber by spraying the fuel into the airstream passing through the throttle body (throttle-body injection) or into the air flowing through the port to the intake valve (port injection).
In a diesel engine, the fuel is injected directly into the combustion chamber (direct injection) or into a smaller connected auxiliary chamber (indirect injection). Metering of the fuel charge may be performed mechanically or electronically. The pressurized delivery of a metered amount of fuel into the intake airflow or combustion chambers of an internal combustion engine. McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
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