Mixture Preparation and HC Emissions of a 4-Valve Engine with Port Fuel Injection During Cold Starting and Warm-up

Takeda, Keiso; Yaegashi, Takehisa; Sekiquchi, Kiyonori; Saito, Kimitaka; Imatake, Nobuo

doi:10.4271/950074

Cited by 97 publications

(22 citation statements)

References 7 publications

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“…Another mechanism by which mixture preparation may influence HC emissions is the storage and subsequent vaporization of liquid fuel on the walls and in the piston ring crevices. [17] have shown that liquid fuel droplets of 30 p.m or larger which flow into the cylinder will impinge on the walls of the combustion chamber, cylinder liner, and piston crown and cause wall wetting. At normal operating conditions most of the liquid fuel in the cylinder was found to vaporize and mix with the cylinder charge during intake and compression.…”

Section: Poor Mixture Preparationmentioning

confidence: 99%

Contribution of Oil Layer Mechanism to the Hydrocarbon Emissions from Spark-Ignition Engines

Linna

Målberg

Bennett³

et al. 1997

SAE Technical Paper Series

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One mechanism by which some fuel may escape the main combustion process in spark-ignition engines and be exhausted as unburned hydrocarbons is by absorption in the lubricating oil on the cylinder liner. The importance of this mechanism is, however, uncertain. Modeling studies suggest that the process can take place within an engine cycle, and that the amount of fuel absorbed in the oil layer is significant. Investigations in combustion bombs, and engines operated without lubricant indicate that this contribution is substantial. However, several researchers have reported no significant effect, when using combinations of fuels and oils with very different solubility characteristics.This study comprise the results from several experiments and modeling efforts. A ten component synthetic fuel, and different lubricants formulated to study the effect of base stock and viscosity were tested. The predicted variation in oil layer thickness caused by viscosity differences, were of the order of 20-40%. Steady state engine tests were carried out at three different coolant temperatures using a single cylinder engine with the combustion chamber of a production engine. A piston with reduced ring-pack crevices, and a cylinder head gasket designed to line up flush with the liner, were used to minimize the combustion chamber crevice volumes, and thus focus on HC derived from the oil layer mechanism. In addition to total HC, speciated engine-out emissions were recorded for the cold operating condition.Critical unknown physical parameters for the fuel components and lubricants were experimentally determined. Head space gas chromatography was used to measure solubilities, and Nuclear Magnetic Resonance was used to establish diffusion rates. Numerical modeling was employed to estimate the oil layer thickness, and the absorption rates for the individual fuel components. The estimated differences in absorption rate or "source strength" for the different lubricants, as caused primarily by different oil layer thickness, and fuel-oil solubility were of the order of 20%. The speciated emissions showed some sensitivity to oil layer thickness at low load and speed, with thicker oil layers producing more of the heavy, i.e. more soluble, fuel components. At higher loads and speeds speciated emissions showed very little to none sensitivity to oil layer thickness. For total engine-out HC, i.e. fuel and non-fuel HC, no significant effect of oil layer thickness, or calculated source strength, was observed at any of the operating conditions, contrary to what would be expected if fuel-oil absorption was contributing significantly to engine-out HC. Thus these results do not support oil layer mechanism as a significant source of unburnt hydrocarbons in the tested engine.

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Section: Poor Mixture Preparationmentioning

confidence: 99%

Contribution of Oil Layer Mechanism to the Hydrocarbon Emissions from Spark-Ignition Engines

Linna

Målberg

Bennett³

et al. 1997

SAE Technical Paper Series

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“…Since only a small portion of injected fuel vaporizes and contributes to the combustible mixture in a cold engine [2,3], the cold start-up process of port fuel injected SI engines generally involves significant over-fueling in the intake port. A substantial amount of fuel is injected to overcome unexpected transients as well as poor mixture preparation.…”

Section: List Of Tablesmentioning

confidence: 99%

Effects of Secondary Air Injection During Cold Start of SI Engines

Lee

Heywood

2010

SAE Int. J. Engines

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The paucity of exhaust oxygen during cold start of automobile SI engines limits the extent of exothermic chemical reactions in the exhaust port, manifold, and catalyst. The injection of air into the exhaust system therefore could be an effective way to utilize additional thermal and chemical energy available in the exhaust gas. This study investigates the thermal and chemical processes associated with secondary air injection (SAI) inside the exhaust system in order to fully exploit the simultaneous benefits of reducing converter-in emissions and improving catalyst lightoff performance during cold start.An experimental study was performed to develop a more fundamental understanding of the effects of SAI on exhaust gas emissions and catalyst light-off characteristics during cold start of a modern SI engine. The effects of several design and operating parameters such as spark retardation, fuel enrichment, secondary air flow rate and air injection location were investigated to understand the mixing, heat loss, and thermal and catalytic oxidation processes associated with SAI. Timeresolved HC, CO and CO 2 concentrations were tracked from the cylinder exit to the catalytic converter outlet and converted to mass flow rates by applying an instantaneous exhaust mass flow rate model. A phenomenological model of exhaust heat transfer combined with the gas composition analysis was also developed to define the thermal and chemical energy state of the exhaust gas with SAI.The study found that significant emissions reduction can be achieved with SAI by the thermal oxidation process prior to the catalyst, which results in enhancing the chemical process inside the catalyst by faster catalyst light-off. The engine operation, with a relative air/fuel ratio 20% rich of stoichiometric and 100% secondary air, yielded the fastest catalyst light-off (4.2 sec). The SAI system reduced HC emissions by 46% to 88% and CO emissions by 37% to 93% compared with the normal operating conditions. The analysis showed that the post-catalyst HC emissions levels were optimized with secondary air flow rates corresponding to an overall exhaust lambda of 1.3.

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“…Since only a small portion of injected fuel vaporizes and contributes to the combustible mixture in a cold engine [3,4], the cold start-up process of port fuel injected SI engines generally involves significant over-fueling in the intake manifold. A substantial amount of fuel is injected to overcome unexpected transients as well as poor mixture preparation.…”

Section: Background and Motivationmentioning

confidence: 99%

“…• The fast-response FID was calibrated before and after each experiment using 1500ppmC 3 propane gas (span) and nitrogen gas (zero).…”

Section: Fast-response Emissions Analyzersmentioning

confidence: 99%

Effects of Charge Motion Control During Cold Start of SI Engines

Lee¹,

Heywood²

2006

SAE Technical Paper Series

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Mixture Preparation and HC Emissions of a 4-Valve Engine with Port Fuel Injection During Cold Starting and Warm-up

Cited by 97 publications

References 7 publications

Contribution of Oil Layer Mechanism to the Hydrocarbon Emissions from Spark-Ignition Engines

Contribution of Oil Layer Mechanism to the Hydrocarbon Emissions from Spark-Ignition Engines

Effects of Secondary Air Injection During Cold Start of SI Engines

Effects of Charge Motion Control During Cold Start of SI Engines

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