Pumppipeinjector systems

Engine designs with bore sizes larger than 300 mm can benefit from the advantages of pump/pipe/injector systems. The primary requirement for installation is to minimize the trapped high pressure fuel volume. This is usually achieved by having a high camshaft and the high pressure connection to the injector as low as possible through the cylinder head. The resulting low trapped fuel volume maximizes hydraulic efficiency and responsiveness.

Pressure wave effects in the high pressure passages will still be sufficient to require a delivery valve to eliminate secondary injection and cavitation erosion. Pressure unloading delivery valves have been used for many years and, with experience, have become reliable. The need to create the fastest possible pressure collapse at the end of injection and a trapped residual pressure, and to ensure durability of the valve components, led to a valve design with a series of tailoring features (Figure 8.15). Valve opening pressures, an unloading feature on the pro flow valve and a control orifice can all be used to tune hydraulic performance.

Pump/pipe/injector systems have hydraulic disadvantages but offer flexibility. Elements and valves can be changed relatively easily during servicing and to offer uprating opportunities. Pump/pipe/injector systems also facilitate water injection and high pressure gas injection which are of increasing interest to engine designers.

The nozzle is the interface between the injection system and the combustion process: good nozzle performance is essential for good combustion. The detailed design of the nozzle seat, sac and spray hole entry is vital in minimizing pressure flow losses and maximizing energy in the spray (Figure 8.16). This ensures minimum droplet size and an

Figure 8.15 Typical pressure unloading delivery valve design (Delphi Bryce)

Figure 8.16 Typical nozzle 'sac end' design; low volume for reduced emissions (Delphi Bryce)

even spray distribution and penetration. Abrasive flow machining techniques are typically exploited to secure rounded edges and polished surfaces to improve discharge coefficients.

Major durability and reliability concerns for injection equipment have been cavitation erosion at high pressure spill and element seizure. Cavitation erosion is being addressed by improved delivery valve designs and pressure decay techniques at the barrel port/fuel gallery. To promote seizure resistance at the increased plunger velocities required to generate higher pressures it is necessary to improve element geometries and control surface textures. The use of surface coatings is also becoming widespread.

Programs are available to design fuel cams and analyse unit injector rocker arrangements. The results can be used to predict injection pressure, period and rate. Accurate system modelling is a considerable aid in reducing application development time and cost; a wide range of variables can be analysed with confidence.

Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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