From the view of suppressing the global warming and
environmental pollution, responding to the regulation of fuel
consumption and exhaust gases along with lengthening the
maintenance interval, are becoming more demanded. The development
of a high-performance, long-life spark plug has become essential in
response to these demands. While improved performance (high
ignitability and low required voltage), the discharge part of the
spark plug needs to be reduced in size. But, in the past this has
been difficult because of the limitations of platinum alloys in
terms of wear. Therefore, it has been quite difficult to achieve
both smaller discharge parts and longer life.
To dramatically improve wear resistance, we researched materials
that are both resistant to oxidation and have a high melting point.
This research resulted in our development of a new iridium alloy
(Iridium-10wt%Rhodium).
Through this development we have been able to produce an iridium
spark plug that surpasses the conventional platinum technology. We
set the following two types of spark plugs that could be mass
produced for first time in the world. 1) Ultra-high ignitability
spark plugs (electrode \gF 0.4 mm and same service life as platinum
spark plugs) 2) High ignitability spark plugs (electrode \gF 0.7 mm
and twice the service life of platinum spark plugs)
This paper particularly presents concrete engine evaluation
results for the ultra-high ignitability spark plugs with the
electrode \gF 0.4 mm and proposes examples of improving combustion
by using these spark plugs. For example, improved ignitability
makes possible reduced idling revolutions, larger EGR, leaner
air-fuel mixtures, and emissions.