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Ignition Energy Development for a Spark Initiated Combustion System Capable of High Load, High Efficiency and Near Zero NOx Emissions
Abstract:
Turbulent Jet Ignition is an advanced pre-chamber initiated
combustion system for an otherwise standard spark ignition engine
found in current on-road vehicles. This type of ignition enables
very fast burn rates due to the ignition system producing multiple,
widely distributed ignition sites, which consume the main charge
rapidly. This high-energy ignition system results from the
partially combusted (reacting) pre-chamber products initiating main
chamber combustion. The fast burn rates allow for increased levels
of dilution (lean burn and/or EGR) when compared to conventional
spark ignition combustion, with dilution levels being comparable to
other low-temperature combustion technologies (HCCI) without the
complex control drawbacks.
Previous Turbulent Jet Ignition experimental results have
highlighted peak net indicated thermal efficiency values of 42% in
a standard modern engine platform. Additionally, the pre-chamber
combustion system is capable of tolerating up to 54% mass fraction
diluent at the world-wide mapping point of 1500 rev/min, 3.3 bar
IMEPn (~2.62 bar BMEP), resulting in an 18% improvement in fuel
economy and near-zero engine-out NOx emissions.
This paper focuses on single-cylinder experiments, which reduced
the ignition energy of the spark-initiated pre-chamber combustion
system from 75 to less than 5 mJ. Experimental results highlight
that the pre-chamber combustion system is quite robust and largely
unaffected by ignition energy changes, unlike conventional spark
ignition combustion which typically requires high amounts of energy
(over 50 mJ) under diluted (lean burn/EGR) operation. This occurs
as jet ignition combustion in the heavily diluted main chamber is
driven by the chemical, thermal and turbulent effects of the
propagating jet exiting the pre-chamber and not the flame kernel
growth and subsequent traveling flame front as in spark ignition
combustion. Consequently, results show the potential to
significantly reduce the ignition energy demand and hence ignition
coil and spark plug size for the Turbulent Jet Ignition combustion
system. This has additional benefits in improving component
longevity, reducing ignition system costs and aiding in cylinder
head packaging.