Cogeneration (also combined heat and power, CHP) systems have
become widely used in recent years for reasons such as efficient
use of energy resources and CO₂ emissions reduction. As a power
source in cogeneration, gas engines are widely used. Large gas
engines have a different ignition system from those in medium-sized
and small ones. To burn the fuel mixture to the cylinder wall, many
large gas engines (2MW or more outputs) with wide cylinder-bore
have a pre-chamber. Flame jets from the pre-chamber enable rapid
combustion of super lean mixtures throughout the cylinder walls,
achieving improved heat efficiency. In contrast, many medium-sized
to small gas engines (less than 2 MW outputs) have a general and
simple open-chamber, in which a flame kernel produced by the
electric spark of a spark plug ignites the mixture in the
combustion chamber. Accordingly, open-chamber gas engines are
inferior to pre-chamber gas engines, specifically in rapid and lean
combustion conditions that are intended for thermal efficiency
improvements.
This paper is a report on a pre-chamber spark plug (hereinafter
"PC plug") developed for open-chamber engines. With a
pre-chamber added to a spark plug, the PC plug achieves rapid and
lean combustion as in a pre-chamber engine. Meanwhile, combustion
characteristics and other features have not yet been determined
regarding the use of the PC plugs. In the present study, we
therefore empirically assessed combustion characteristics dependent
on the PC spark plug. This includes plug design and its benefits,
as well as effects of PC plug design factors on combustion. The
result is successful development of a PC plug with remarkably
improved performance relative to standard plugs.