A Packard diesel advertisement which appeared in _Aero Digest_ for June
1930 stated that this engine had three major advantages over its
gasoline rivals: Greater reliability because of extreme simplicity of
design; greater economy because of lower fuel cost plus lower fuel
consumption, permitting greater payloads with longer range of flight;
and greater safety because of removal of the fire hazard through the use
of fire-safe fuel and absence of electrical ignition equipment.
These were the engine's principal advantages. Others are analyzed here
by the author in order of their importance. At low altitudes the diesel
uses an excess of air to eliminate a smoking exhaust; consequently at
high altitudes, where the air is less dense, the diesel is still able to
maintain much of its power. In contrast, the carburetored gasoline
engine is sensitive to the fuel-air ratio and thus has no surplus air
available at higher altitudes. A malfunctioning carburetor could cause a
gasoline engine to cease operating, but an inoperative fuel injector
would cause the Packard diesel to lose one ninth of its power, since
each cylinder had its own independently operating injector. In practice,
however, because of the excessive vibration, the engine was generally
shut off immediately after a cylinder cut out.[27] Shielding was
unnecessary because the diesel had no electrical ignition system.
Carburetor icing was an impossibility because there was no carburetor.
Any excess lubricating oil in a diesel engine's cylinder is consumed
cleanly to produce power. By contrast, such oil in a gasoline engine's
cylinder is only partly burned. As a result carbon deposits form that
eventually cause malfunctioning of the spark plugs, valves, and
combustion chambers. This advantage accrued to the diesel because it
utilized an excess of air, and in addition its cylinder walls were
hotter. The engine was very clean-running from the standpoint of oil
leakage. This was a safety factor since it eliminated the possibility of
a fire starting on the outside surfaces of the engine, and in addition
it saved the time and money that was normally spent cleaning
engines.[28] Since the diesel utilized its heat of combustion more
efficiently than the gasoline engine, its cooling fin area could be
reduced by 35 percent. This permitted better streamlining. Having less
cooling fin area, it warmed up more rapidly than a gasoline engine.
[Illustration: The PACKARD-DIESEL AIRCRAFT ENGINE