fuel injection

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fuel injection

fuel injection, system in an internal-combustion engine that delivers fuel or a fuel-air mixture to the cylinders by means of pressure from a pump. It was originally used in diesel engines because of diesel fuel's greater viscosity and the need to overcome the high pressure of the compressed air in the cylinders. A diesel fuel injector sprays an intermittent, timed, metered quantity of fuel into a cylinder, distributing the fuel throughout the air within. Fuel injection is also now used in gasoline engines in place of a carburetor. In gasoline engines the fuel usually is injected into the intake manifold and mixed with air, and the resulting mixture is delivered to the cylinder. Modern fuel injection systems use computers to regulate the process. Fuel injection results in more efficient fuel combustion, improving fuel economy and engine performance and reducing polluting exhaust emissions.
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fuel injection

[′fyül in‚jek·shən]
(mechanical engineering)
The delivery of fuel to an internal combustion engine cylinder by pressure from a mechanical pump.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

Fuel injection

The pressurized delivery of a metered amount of fuel into the intake airflow or combustion chambers of an internal combustion engine. Metering of the fuel charge may be performed mechanically or electronically. In a diesel engine, the fuel is injected directly into the combustion chamber (direct injection) or into a smaller connected auxiliary chamber (indirect injection). 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). See Combustion chamber

The diesel engine must be supplied with fuel from the injection nozzle at a pressure of 1500–5000 lb/in.2 (10–35 megapascals) for indirect-injection engines, and up to 15,000 lb/in.2 (100 MPa) or higher for direct-injection engines. 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. Extremely accurate fuel metering is necessary, with the start of injection occurring within a precision of up to 1° of engine crankshaft angle. A timing device in the injection pump automatically advances the start of fuel delivery as engine speed increases to optimize the start of combustion.

The intake air is not throttled in a diesel engine, with load and speed control accomplished solely by controlling the quantity of fuel injected. The mean effective pressure developed by combustion is controlled by the volumetric capacity of the injection pump. To prevent an unloaded diesel engine from increasing in speed until it destroys itself, a governor is required to limit maximum engine speed. See Diesel engine, Internal combustion engine, Mean effective pressure

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. 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. 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. This minimizes exhaust emissions. See Carburetor

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. The gasoline fuel injector is an electromagnetic (solenoid-operated) or mechanical device used to direct delivery of or to meter pressurized fuel, or both. A fuel-pressure regulator maintains a controlled fuel pressure at each injector, or a controlled differential pressure across the injector. See Fuel pump, Fuel system

McGraw-Hill Concise Encyclopedia of Engineering. © 2002 by The McGraw-Hill Companies, Inc.

fuel injection

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A form of a fuel-metering system for a reciprocating engine that injects fuel directly into the cylinder rather than mixing it with air before it is taken in through the intake valve. The two types of fuel injection systems are the direct injection system (for diesel engines) and the continuous-flow fuel injection system (for horizontally opposed engines).
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved
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