SHAFT-AXLE 7D7707 - Caterpillar

Dry Natural Gas
Dry natural gas, also known as commercial pipeline natural gas, is a mixture of methane, ethane, propane and butane. The contents of propane and butane are less than 5 percent and 1 percent respectively.
The reference to "dry" is made because the gas has no liquid propane or liquid butane.
The heat content of dry natural gas may change from source to source. Caterpillar-built gas engines are adjusted at the factory with dry natural gas that has a low heat value of 33.72 kJ/I (905 Btu/ft3).
Field Gas
Field gas, also known as wellhead gas, is the gas available at the wellhead in a gas field.
The contents of wellhead gases change from location to location. As a result, the gas from one field may be acceptable for a Caterpillar-built engine while the gas from a different field may not. For this reason, a gas analysis is necessary to find if the fuel should be used.
Wellhead gases which have a minimum of 90 percent methane and ethane and have a remainder no heavier than butane can be used in low compression engines. However, many wellhead gases have some heavier hydrocarbons such as pentane, isobutane and other "gasolines". These heavier hydrocarbons cause knock and other mixture problems, and they can have negative effects on an engine's performance and service life.
Sour Gas
Sour gas is gas that contains sulfur compounds such as hydrogen sulfide (H2S). Gases that have no sulfur compounds are known as sweet gases.
The use of gases that have hydrogen sulfide can damage the engine. Water vapor and sulfur oxides, which are products of combustion, chemically unite to make sulfurous and sulfuric acids. These acids destroy internal engine components such as oil coolers, valve guides, piston pin bushings, piston rings and cylinder liners. History has shown that oil coolers often are the first components affected by the acids.
Before sour gas is used to fuel an engine, the gas should be analyzed. If it has more than 0.1 percent by volume of hydrogen sulfide, the gas should be cleaned (scrubbed) to decrease the hydrogen sulfide content to below 0.1 percent.
When sour gas is used, steps should be taken to decrease the effects of sulfur compounds. Caterpillar's recommendations are: 1. Keep the engine outlet coolant temperature between 88° and 93°C (190° to 200°F). A temperature increase of 8.3°C (15°F) across the engine is acceptable, but an increase of 5.6°C (10°F) is best. Lower jacket water temperatures permit water vapor and hydrogen sulfide to condense on the cylinder liners and make acids. Higher temperatures will decrease this condensation.
Generally, engines equipped with inlet-controlled cooling systems will keep the coolant in the correct temperature range. Engines equipped with outlet-controlled cooling systems may need added external controls to keep the coolant temperature within the acceptable range.
A set of thermostatically-controlled shutters on the engine coolant radiator or heat exchanger is the most effective device for controlling the engine temperature. Shutters should be considered for installations designed to operate on sour gas. Some field gathering units which are subjected to