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A Normally Aspirated Spark Initiated Combustion System Capable of High Load, High Efficiency and Near Zero NOx Emissions in a Modern Vehicle Powertrain
Journal Article
2010-01-2196
ISSN: 1946-3936, e-ISSN: 1946-3944
Sector:
Topic:
Citation:
Attard, W. and Parsons, P., "A Normally Aspirated Spark Initiated Combustion System Capable of High Load, High Efficiency and Near Zero NOx Emissions in a Modern Vehicle Powertrain," SAE Int. J. Engines 3(2):269-287, 2010, https://doi.org/10.4271/2010-01-2196.
Language:
English
Abstract:
Turbulent Jet Ignition is an advanced spark-initiated
pre-chamber combustion system for an otherwise standard spark
ignition engine found in current on-road vehicles. This
next-generation pre-chamber design simply replaces the spark plug
in a conventional spark ignition engine. Turbulent Jet 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) prechamber 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 light-load results at the
worldwide mapping point (1500 rev/min, 3.3 bar IMEPn) have
demonstrated an 18% improvement in fuel economy, with single digit
ppm engine-out NOx emissions. This paper focuses on performance,
efficiency, emissions and combustion effects of a Turbulent Jet
Ignition system operated at unthrottled conditions with load
variation achieved by altering the dilution level (excess air
and/or EGR).
Turbulent Jet Ignition single-cylinder experimental results at
1500 rev/min highlight a matched load operating range when compared
to conventional spark ignition combustion, with identical peak BMEP
and the ability to operate in an unthrottled mode down to 3.9 bar
IMEPn with increasing dilution levels.
The high diluent fraction and resultant low temperature
combustion has resulted in a peak indicated net thermal efficiency
of 42% to be recorded together with near zero engine-out NOx
emissions. This was achieved utilizing the engine's standard
PFI fuel delivery system and a relatively low compression ratio of
10.4. Efficiency gains are attributed to a combination of
combustion improvements, reduced heat losses and the near
elimination of dissociation associated with low combustion
temperatures. Peak efficiency improvements equate to an 11%
relative improvement when compared to conventional stoichiometric
spark ignition combustion. Results also indicate that jet ignition
combustion has the potential to exceed 45% indicated net thermal
efficiency (19% relative improvement) with a CR increase to ~14.
The CR increase is made possible by the burn rate improvement
associated with the distributed ignition system and the addition of
side, wall-guided DI. This would exceed the HCCI peak thermal
efficiency of 43% in the same engine platform as there is no
requirement to switch back to conventional spark ignition
combustion at high load operation, which limits HCCI maximum CR for
knock avoidance.