Fuel Selection

There are several factors to consider when selecting the fuel for use with engine generator sets.  Use the comparison chart and information below for a rough guide.

Fuel Comparison Chart

Gaseous Fuels

Gasoline Fuel

Diesel Fuel

Fuel Energy Content & Conversions

Fuel Comparison Chart

 

Gaseous Fuels

Gaseous fuels such as natural gas, vapor propane and liquid propane are the most common choice for small automatic standby generators.  This is because the engines are economical to build, these fuels provide good starting reliability and they are in common use and available everywhere.  When purchasing a gaseous fueled genset you must remember the following:

• Specify which kind of fuel you will be using when placing the order.
  If there is a mistake it may NOT be possible to convert a genset in
  the field between natural gas/vapor propane and liquid propane.
  It usually IS possible to convert between natural gas and vapor
  propane however.

• If you order a genset for vapor propane it is usually set up at the
  factory for natural gas and MUST be converted in the field to vapor
  propane.  The installation manual will describe the steps for this
  simple conversion which usually involves connecting a fuel line to
  another port or changing an orifice and a mixture setting.  If you
  fail to make this conversion the genset will not run properly and
  may not start at all.

• A vapor propane system draws the fuel from the TOP of the tank
  usually through a pressure regulator at the tank.  The liquid in the
  lower part of the tank must be able to absorb sufficient heat from
  the tank surroundings for vaporization to take place.  Therefore, it
  is important that the tank has enough exposed surface area for this
  heat transfer.  There can be a problem of insufficient fuel flow in
  very cold weather or if the tank is less than half full or is too small.
  In practice this only is an issue in the far northern areas of the USA.

• A liquid withdrawal propane system draws the liquid from the BOTTOM
  of the tank and small high pressure tubing is used to carry it to the
  genset.  The genset is then equipped with a special device to vaporize
  the fuel before combustion.  This eliminates the low temperature
  vaporization concerns at the tank in cold climates.  However it may
  complicate using propane for other appliances since it is being supplied
  in liquid form to the point of use.

 

Gasoline

The gum deposits that gasoline forms when it is stored can cause problems in fuel filters and carburetors, especially in cold weather and when the engine is not operated often enough.  There are gasoline additives that can reduce this problem, such as Stabil.

 

Diesel

Diesel fuel has traditionally been used in many automatic standby generator applications.  As long as the engine is kept warm when it is not running, starting reliability can be excellent.  However, there are now emissions limitations in some areas that make it difficult for a diesel permit to be approved.  There are also costs associated with fuel spill prevention and containment.

 

Fuel Energy Content & Conversions

Here are some approximate energy conversion factors.  The exact values will vary depending on the quality of the fuel and in some cases the pressure.  SCF and SCFH are abbreviations for standard cubic feet and standard cubic feet per hour.

Propane

1 gallon = 91,500 BTU
1 cubic foot = 2,500 BTU
1 pound = 21,500 BTU
4.24 lbs = 1 gallon
36.39 cubic feet = 1 gallon

Natural Gas

1 cubic foot = 1,050 BTU

Gasoline

1 pound = 19,000 BTU
1 gallon = 125,000 BTU
1 gallon = 6.1 lbs

Oils

1 gallon kerosene = 135,000 BTU
1 gallon #2 oil = 138,500 BTU
1 gallon diesel = 139,200 BTU
1 gallon #6 oil = 153,200 BTU

Other Fuels (dry)

1 lb hydrogen = 51,892 BTU with steam as product
1 lb coal (anthracite) = 12,700 BTU
1 lb coal (subbituminous) = 8,800 BTU
1 lb coal (bituminous) = 11,500 BTU
1 lb pine wood bark = 9,200 BTU
1 lb hardwood bark = 8,400 BTU
1 lb wood = 7,870 BTU
1 lb dung = 7,500 BTU
1 lb waste paper = 6,500 BTU
1 lb sawdust/shavings = 3,850 BTU
1 kWH electricity = 3,413 BTU
1 therm any fuel = 100,000 BTU

 

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