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Towards an Innovative Combination of Natural Gas and Liquid Fuel Injection in Spark Ignition Engines
Abstract:
In order to address the CO₂ emissions issue and to diversify the
energy for transportation, CNG (Compressed Natural Gas) is
considered as one of the most promising alternative fuels given its
high octane number. However, gaseous injection decreases volumetric
efficiency, impacting directly the maximal torque through a
reduction of the cylinder fill-up.
To overcome this drawback, both independent natural gas and
gasoline indirect injection systems with dedicated engine control
were fitted on a RENAULT 2.0L turbocharged SI (Spark Ignition)
engine and were adapted for simultaneous operation. The main
objective of this innovative combination of gas and liquid fuel
injections is to increase the volumetric efficiency without losing
the high knocking resistance of methane.
This paper describes how the CIGAL™ (Concomitant Injection of
Gas And Liquid fuels) concept can generate a synergy effect between
both fuels, which allows combustion efficiency to be increased
significantly on turbocharged SI engines. Indeed, the gas and
gasoline resultant mixture can be injected in stoichiometric
conditions even at full load with spark timing set close to MBT
(Maximum Brake Torque), thus leading to excellent performances,
compliance with stringent regulations, good specific consumptions
and reduced CO₂ emissions.
This injection strategy can also be extended to other liquid
fuels, such as ethanol, and gaseous fuels like LPG (Liquid
Petroleum Gas): the purpose remains having the best distribution
between gas and liquid injections in order to maximize their
advantages. Like for methane and gasoline, a strong synergy was
observed with LPG and gasoline concomitant injection, leading to
lower specific consumptions compared to those obtained in single
fuel injection.
This study demonstrates that the concept of concomitant
injection offers direct benefits on the autonomy management of gas-
and gasoline-powered vehicles. It also opens very interesting
perspectives for meeting future emission regulations using only a
3-way catalyst since stoichiometry is maintained over the whole
engine operating range.