As more and more mobile and stationary generator applications shift away from liquid fuels like diesel and heavy fuel oil, there is an increasing demand for other portable or storage-friendly gaseous fuels where pipeline natural gas is generator fueling

  not a logistical 
option. Additionally, for certain generator models, there are dual-fuel capabilities where natural gas and propane are both connected. The growth of gaseous, carbon-based fuels for generators has brought with it several challenges and inconsistencies in descriptions, definitions, and specifications. We’ll explore the topic of LPG in this white paper to provide some clarity around some terms that are commonly used in the industry. So first let’s start with some basic industry-accepted and used definitions:

  ready for usage as a fuel. This can be done via temperature or pressure; however, pressure is the normal process to liquify it, requiring about 175psig of pressure at 100°F to keep it in liquid state.

   This is propane in its vaporous form, once it has been released from the storage tank. Due to its low boiling point, liquid propane will vaporize as soon as it is vented from its storage tank. Oftentimes generators will use additional vaporizers heated by engine jacket water to ensure that propane (and any other heavy hydrocarbons with it) will be in vapor form prior to entering the carburetor. This is common in oil and gas applications with high Btu wellhead gases.

  This acronym is used to describe liquid petroleum gas, which has no specific or controlled global definition regarding constituents and tolerances. The definition is representative of the source of these gases as a common byproduct of natural gas processing and petroleum refining. LPG gases are most heavily comprised of propane and butane, both iso-butane and normal-butane. These two gases can vary in LPG from nearly 0% to 100% composition and still be referred to as LPG. 

Some examples of LPG would be:

50% propane, 25% iso-butane, 25% n-butane

90% propane, 5% butane, 5% other

80% butanes and 20% propane.

The exact composition (HD-5) of LPL or LPV also fit within this broad definition. More on this later.

  This has been used to describe both LPL and LPV, but usually it is meant to represent LPV. If a document or specification lists only LP, it is always helpful to ask for clarification.

From a gas engine perspective, it is critical that it is provided with a consistent quality of supply, and it is also well understood that different hydrocarbons burn at different rates within the combustion chamber. That is why almost all gas engine manufacturers and therefore generator providers work with the well-defined and widely accepted HD-5 propane definition per ASTM D1835 and GPA 2140. In its simplest form the HD-5 
standard allows for:

Minimum of 90% propane content, 

Maximum of 5% propylene, (this is limited to minimize sticking in fuel system components)

Maximum of 2.5% butane and heavier, and

The remainder is fulfilled by other gases like inerts, methane, etc.

​All Generac SG and MG stationary gas generators that are approved for use on propane would be allowed only under the HD-5 specification, which is also documented in Generac specification A0000641396, latest edition. The MGG series of prime stationary and mobile gas generators are also built with a secondary fuel system that would require HD-5 propane.

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