Engine starting control system and method

Abstract

Various example approaches are described, one of which includes a method for controlling injection of gaseous and liquid fuel to a cylinder during engine starting. Specifically, gaseous fuel is injected during or before an intake stroke of the cycle to form a well-mixed overall lean air-fuel mixture, and then liquid fuel is directly injected to the cylinder at least during one of a compression and expansion stroke of the engine cycle to form a rich air-fuel cloud near the spark plug, where a spark initiates combustion of the injected fuels. In one example, the rich cloud enables additional spark retard, and thus faster catalyst light-off, while maintain acceptable combustion stability of the gaseous fuel.

Description

【Technical Field】 [0001] The invention relates to an engine system and a control method thereof. 【Background technique】 [0002] During engine start, a variety of methods can be used to thoroughly mix air and fuel in the cylinder to provide more complete combustion and thus less emissions of multiple exhaust components. For example, some vehicles may be operated on liquid fuel or gaseous fuel or both. In these systems, existing methods teach that, especially during engine start, compared to liquid fuel, gaseous fuel can be preferably used to improve mixing, especially during engine cold start (not warming up) conditions. For example, refer to US Patent No. 5,566,653. [0003] However, the inventor of the present invention has recognized some problems caused by this method. As an example, when spark retard is used to promote an increase in exhaust gas temperature and thereby catalyst light-off is faster, the magnitude of spark retard may be defined by the fuel characteristics of ...

AI Technical Summary

Problems solved by technology

That is, when the air-fuel ratio of fresh air to gaseous fuel is set slightly lean of stoichiometry (to reduce NOx formation), there are essentially no rich pockets due in part to the well-mixed state of the gaseous fuel (rich pockets can assist ignition), which limits the amount of spark retard

In other words, using gaseous fuels for engine starting presents a paradox that improved mixing of gaseous fuels helps reduce engine emissions due to more complete combustion, however it degrades the engine by increasing exhaust heat (which is used for more rapid the ability to elevate the temperature of the exhaust catalyst used to react with engine emissions)

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