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450 Lawerence K. Wang et al.

Fig. 1. Porsche combustion chamber inlet.

chamber. This, however, would cause increase overlap and rough operation at low speeds
and idle. To overcome the problem, tapered cams operated by centrifugal governor control
are being developed to provide variable valve timing and lift.
Carburetion has always been a problem in that all cylinders cannot be utilized with
effectiveness by one atomization device per engine. As an alternative to having several
carburetors per engine, systems that will improve atomization are being evaluated.
Ultrasonic atomization is one system under study. Another is a catalytic carburetor,
which cracks the gasoline to produce a more gaseous fuel for combustion instead of
atomized liquid droplets.
One of the newest innovations is the development of a system to permit an eight-
cylinder engine to operate on, for example, four, five, six, seven, or eight cylinders. This
is accomplished by the use of an electronic control to close the valves of cylinders not
being used. For example, during cruising periods, only four cylinders would normally
be used, whereas when acceleration or load requirements increase, more cylinders
would activate to provide the needed extra power.
3.4.2. Diesel Engines
Diesel engines appear to have the ability to meet the HC, CO, and NO standards of
x
the 1980s. Because of their higher compression ratios, these reciprocating compression
ignition engines are more efficient than gasoline engines and they can burn a cheaper
grade of fuel owing to the positive-timed fuel-injection systems. These engines have not
been widely accepted for automotive use because of their poorer performance and noise
problems. It is the dominant engine for all land propulsion systems larger than the
passenger automotive engine and in all ships except small pleasure craft. Diesel engines
also serve a large portion of the emergency power generation systems.