111 Introduction

Often called 'the heart of the engine', the fuel injection system is without any doubt one of the most important systems. It meters the fuel delivery according to engine requirements, it generates the high injection pressure required for fuel atomization, for air-fuel mixing and for combustion and it contributes to the fuel distribution in the combustion system-hence it significantly affects engine performance emissions and noise.

The components of the fuel injection system require accurate design standards, proper selection of materials and high precision manufacturing processes. They lend themselves to mass production techniques and they become complex and costly.

As the applications of diesel engines diversified so did the fuel injection systems. Along with the conventional pump-line-nozzle systems new concepts evolved such as distributor pumps, common-rail systems, accumulator systems, unit pumps, unit injectors, etc. In addition, the 'intelligence' of electronics enhanced the capability of the 'muscle power' of hydraulics making the combustion system much more flexible and responsive to new parameters: pressure, temperature, engine speed, etc. Combustion can be thus optimized for best performance, emissions, smooth operation etc., according to the needs of the application. Through electronics, the fuel injection system can interface with other systems; automatic transmissions, cruise control, turbocharger operation, traction control, exhaust aftertreatment, etc. in an integrated system approach.

The net result of this integration is an advanced diesel engine with high power density, very low emissions, low noise and superior drivability. Probably the most dynamic application of advances in fuel injection and electronic management is in the area of light-duty vehicles (passenger cars, light trucks, sport utilities) where constraints of high performance, low emissions, low noise, low cost, etc., render optimization very challenging.

The research and development in fuel injection systems continues at a very sustained pace. The following sections illustrate several examples of state-of-the-art and near term prospects in fuel injection-from the perspective of major manufacturers.

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