The fuel system on a diesel engine is a highly specialized set of components which…
As mentioned earlier in the Basic Fuel System description, Cat diesel engine fuel delivery systems are designed to deliver more fuel to the engine than is required for combustion, with the excess being returned to the fuel tanks. This
excess fuel, on many engines, is used for cooling and lubricating of the pumps and injection systems and in doing so picks up engine heat and can raise the temperature of the fuel in the tanks.
As previously specified, engine power will be reduced if the fuel temperature exceeds the maximum limit because of the expansion of the fuel (low viscosity). With very low viscosity, the oil loses the capability to lubricate and damage to the injection components will occur.
Proper considerations regarding fuel tank location and size will help temperature control. If the tank is properly located and sized so the accumulated heat will not be objectionable when temperature stabilizes, then nothing more needs to be done. If the stabilized fuel tank temperature is high, the returning fuel should be cooled.
The following factors affect the need for fuel cooling equipment.
- Length of periods of continuous operation; If the operating periods are short, the amount of heat returned to the fuel tanks will be relatively small. Fuel coolers are not generally required for engines used in applications requiring intermittent operation.
- Length of time between periods of operation; if the time between periods of operation is long, the heat will
have an opportunity to dissipate.
- Volume of the fuel tank; If the volume of the fuel tank is large (larger than 11 000 L [3,000 gal]), it will accept a
great deal of heat before the temperature of the fuel leaving the tank increases significantly.
Note: Day tank sizing is critical to maintain the desired fuel supply temperature. Fuel coolers may be required. For a more detailed discussion of required fuel tank volume, see the Day Tank Sizing (When Serving as a Heat Sink) section in Appendix 1.
- Ability of the fuel tanks to dissipate heat. In marine applications for instance, fuel in contact with the shell plating, where at least 10% of the inside surface area of the tank is shell plating, the heat will be easily dissipated and the stored fuel temperature will remain within a few degrees of the ambient water temperature.
A plate type heat exchanger may be used with titanium plates for seawater cooling or stainless steel plates for fresh water cooling.
Refer to Sea Water Systems in the Cooling Systems Application and Installation Guide for proper installation and maintenance procedures of fuel cooler in sea water applications.