The only fuel used for automobile operation is
specially formulated gasoline, even though diesel fuels are used for many
trucks and buses and a few automobiles. The things in a good fuel for
automobile are proper volatility, sufficient antiknock quality, and freedom
from polluting by-products of combustion.
The volatility is reformulated seasonally by refiners so that sufficient
gasoline vaporizes, even in extreme cold weather, to permit easy engine
starting. Antiknock compounds, principally tetraethyl lead, were added to
most gasolines to prevent knocking, a rapid, uncontrolled burning in the
final stages of combustion that results in a characteristic "knock,"
or pinging noise, and may damage an engine or reduce its performance.
Small lead deposits on such places as engine-valve seats improve valve
life. Antiknock quality is r
ated by the octane number of the gasoline and depends primarily on the
compression ratio of the engine. However it is also affected by
combustion-chamber design and chamber-wall deposits. In the early 1990s
regular gasoline carried an octane rating of 87 and high-test in the
neighborhood of 93.
Lubrication is an essential requirement for all vehicles. In its absence,
friction would increase power consumption and damage the parts. The
lubricant also serves as a coolant, a noise-reducing cushion, and a sealant
between engine piston rings and cylinder walls. The engine lubrication
system includes a gear-type pump that delivers filtered oil under pressure
to a system of drilled passages leading to various bearings. Oil spray also
lubricates the cams and valve lifters.
Fairly stiff grease is required by wheel bearings and universal joints. The
other chasis joints require a soft grease that can be injected by pressure
guns. A special grade of light hydraulic fluid is required by hydraulic
transmissions. Manually shifted transmissions use a heavier gear oil similar
to that for rear axles to resist heavy loads on the gear teeth. Gears and
bearings in lightly loaded components, such as generators and window
regulators, are fabricated from self-lubricating plastic materials.