Understanding Diesel Fuel Storage Requirements

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Understanding Diesel Fuel Storage Requirements

Diesel Generator Sets

A basic diesel-fueled genset includes a diesel engine and an electric generator. The mechanical energy provided by the diesel engine turns the generator rotor to produce power in the generator stator windings. The diesel engine itself is an internal combustion engine with various subsystems such as the cooling system, starting system, speed control system, lubrication system, and the fuel system.

The genset typically has a control panel, which is fitted with switches and gauges to operate the generator, such as the start-shutdown controls. In addition, it provides a set of displays for various parameters such as voltage, current, and frequency. The control panel can also include functions to monitor engine parameters such as temperature, speed, oil pressure, and more. The microprocessor within the control panel can be programmed to sense the engine parameters and take corrective action, including engine shutdown.

Diesel Fuel System

In many diesel gensets, an engine-driven fuel pump provides fuel to the fuel injectors via a fuel filter for combustion in the cylinder. The fuel injector is a precision component and has the capability of pumping, metering, and injecting the correct amount of fuel in the combustion chamber. Fuel continually flows in the supply line to the injectors and the excess fuel is returned to the fuel tank through a pressure regulator. The pressure regulator ensures that correct fuel pressure is maintained at the inlet to the injectors.

Another fuel system design utilizes a slightly different arrangement, with the fuel injection pressure being created external to the unit injectors by means of a high-pressure fuel pump. In this arrangement, fuel is not continually circulated through the supply line. Instead, a small amount of fuel is bypassed during fuel injection and this bypassed fuel is returned to the fuel tank. Due to high pressure in the fuel supply, the fuel temperature increases, and the bypassed amount is therefore passed through a cooler before it is returned to the fuel tank.

Diesel fuel temperature must be controlled to a maximum of 66C (150.8F) to ensure that injectors do not plug due to coking and to maintain the fuel viscosity within prescribed limits. Similarly, for cold-weather applications, fuel heaters are required to maintain fuel viscosity and prevent injector plugging due to wax formation.

Diesel Fuel Storage and Supply

According to NFPA 30, storage requirements are based on whether the liquid fuel is “combustible” or “flammable” as assessed by the fuel flash point. The fuel flash point is the lowest temperature at which the fuel will ignite in the presence of an ignition source. NFPA 30 defines combustible liquids as having a flash point equal to or greater than 100F (37.8C) and flammable liquids as having a flash point less than 100F (37.8C).

The flash point of conventional diesel fuel typically ranges between 126F and 204F (52.2C and 95.5C). Therefore, diesel fuel is considered a combustible liquid. It is further classified as Class II if the flash point is less than 140F or Class III if flash point is greater than 140F, depending on the specific fuel.

However, it is important to note that when diesel fuel is blended with ethanol (E-diesel) to reduce emissions, the blended diesel fuel has a low flash point of about 68F (20C). The blended fuel is therefore considered a flammable liquid, requiring management of associated fire and explosion hazards. For simplicity, this article considers only conventional diesel fuel.

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