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designs now have reached the point where further increase in
pressure will produce pre-ignition and detonation.
To overcome this and get higher cylinder pressures and
horsepowers, engine manufacturers now are chilling
combustion air between the supercharger and the cylinder. This
work was first started on the diesel cycle. Excellent results are
being reported.
Engine cooling is also undergoing radical changes. A few
years ago, low cooling water volumes and temperatures were
general. Temperature rises across the engine of 20°F to 30° F were
not uncommon. Today higher water volumes and temperatures
are a must. A temperature rise across the engine of more than
10°F is generally considered prohibitive.
Fuels. The Otto cycle or 4-cycle gas engine is probably the
most versatile drilling engine today. By ordering an engine fitted
with a natural gas carburetor one is able to use natural gas. If
this fuel is not available either butane or propane can be used.
Natural gas, butane and propane are all efficient under the
same compression ratios. This means that the same cylinder
heads would be used for all these fuels. If one wished to use
gasoline in an engine it would be necessary to change to cylinder
heads designed especially for gasoline to get maximum engine
efficiency.
Temperatures. The combustion engine being a heat
machine, temperatures are with a doubt one of the most, if not
the most important feature governing its life, reliability and cost
of operation.
A range of water temperatures leaving the engine is
rather narrow. As temperature increases, the thermal
efficiency of the engine increases up to about 200°F plus. When
the boiling point is exceeded, an entirely new concept of cooling is
put into operation. Boiling heat transfer then cools the engine.
Power output increases again to a point greater than obtainable
with direct liquid phase cooling. As it is impossible to keep a

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