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Author Topic: Fitting LPG - Sizing and Drilling LPG Injectors  (Read 6543 times)

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Kevin Wood

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Fitting LPG - Sizing and Drilling LPG Injectors
« on: 08 April 2010, 10:28:42 »

LPG injectors such as the Valtek type 30 usually supplied with the Stag kits are designed to work with a wide range of engine power outputs and so a way to calibrate the rate of fuel delivery to suit the engine is required.

Fuel flow from an injector is controlled primarily by the time for which the ECU holds it open during the induction stroke of the engine and the pressure of LPG vapour with which it is supplied.

If the injector is delivering fuel too fast for the engine, it becomes impossible to achieve a short enough injection time to accurately control the mixture and the engine will idle poorly and emissions will suffer.

Conversely, an injector what is not able to flow fuel fast enough might end up open 100% of the time as the engine approaches maximum RPM at full throttle, and be unable to supply any more fuel. The engine may have a lean fuel mixture as a result and, at full throttle, this can cause burnt out valves and piston crown damage due to excessive combustion temperatures.

In order to calibrate the injectors to the requirements of the engine a small brass nozzle is fitted at the outlet of each injector valve. These nozzles should not be confused with the nozzles installed in the intake manifold to inject the fuel into the intake. The brass nozzles can be drilled out to various sizes and in so doing the rate of gas flow through the valve is set.

This can be regarded as a coarse adjustment of the fuel flow. Finer adjustments can be made by adjusting the pressure of the vapouriser output, and by adjusting the injector opening time by adjusting the map in the LPG ECU.

The nozzles are normally supplied with very small drillings and it is necessary to drill out the nozzles before installation to achieve sufficient fuel flow on all Omega engines.

The Stag manual contains a table of nozzle diameters against horsepower output per cylinder. In practice, it has been found that a 2.5mm nozzle diameter is a good starting point for a 2.5 or 2.6 V6 engine and, for all others, 2.8 - 3.0 mm works well.

« Last Edit: 12 April 2010, 12:05:29 by Kevin_Wood »
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