Abstract
This article analyzes the influence of the ignition retardation on the fuel consumption, the cumulative tailpipe hydrocarbon emissions, and the temperature inside the three-way catalytic converter in a gasoline direct injection engine operated under idling conditions. A dedicated cylinder-individual, model-based, multivariable controller was used in experiments in order to isolate the effect of the ignition retardation on the hydrocarbon emissions as much as possible. An optimal control problem for a gasoline engine at a cold-start is formulated, which is used to interpret the experimental data obtained. The corresponding goal is to minimize the fuel consumption during an initial idling phase of a fixed duration while guaranteeing that the three-way catalytic converter reaches a sufficiently high final temperature and at the same time making sure that the cumulative hydrocarbon emissions stay below a given limit. The experimental data indicates that the engine should be operated with maximum ignition retardation in order to reach any temperature inside the three-way catalytic converter as quickly as possible concurrently with minimum tailpipe emissions and with the minimum possible fuel consumption.
Highlights
Gasoline engines can be used with a three-way catalytic converter (TWC) as the sole exhaust gas aftertreatment system when operated at a stoichiometric air-to-fuel ratio
A model-based multivariable reference-tracking controller has been designed that allows reproducible measurements to be taken at varying degrees of ignition retardation while the engine is idling, which represents the initial idling phase of an emission test procedure
The experimental data is used to illustrate the correlation between fuel consumption, cumulative tailpipe hydrocarbon emissions, and the time required until the TWC has reached a certain temperature
Summary
Gasoline engines can be used with a three-way catalytic converter (TWC) as the sole exhaust gas aftertreatment system when operated at a stoichiometric air-to-fuel ratio. TWCs have proven to successfully cope with the ever more stringent emission limits, being able to convert more than 95%. Of the relevant raw engine-out emissions under nominal operating conditions [1]. A large portion of the raw engine-out emissions are emitted into the atmosphere untreated. These unfavorable conditions occur during the first 40 to 100 s after the cold-start of an engine, that is, during the phase in which the temperature of the TWC is below light-off. Studies show that among all relevant emissions, namely carbon monoxide, nitric oxides and hydrocarbons, the total hydrocarbon emissions during a complete test procedure are affected most by this first phase of an engine start. The hydrocarbon emissions during this first phase make up 60–80%
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