Reduction of cold-start emissions and catalyst warm-up time with direct fuel injection

Abstract

An internal combustion engine employs fuel injectors positioned to inject fuel directly into combustion chambers of the engine, and an electronic engine controller (EEC) to control operation of the engine. The EEC implements a cold start routine which controls the amount of fuel injected, the time at which the fuel is injected and spark timing to achieve a rapid increase in temperature of the engine and the exhaust system components, thereby decreasing tailpipe hydrocarbon emissions during cold start.

Description

FIELD OF THE INVENTIONThis invention relates to the field of electronic engine control and more particularly to the field of reducing hydrocarbon emissions during cold start in a spark ignited internal combustion engine which employs direct fuel injection.BACKGROUND OF THE INVENTIONA disproportionately large amount of the hydrocarbons produced by a vehicle are emitted during cold starting of the vehicle engine. The temperature of the intake passages and the combustion chambers of the engine during the early stages of a cold start inhibit the proper vaporization of fuel. As a result, during cold start, a stoichiometric air / fuel ratio is difficult to achieve with intake port fuel injection. In addition, unburned fuel vapor is delivered to the catalytic converter together with the normal by-product of combustion. During the early stages of a cold start, the catalyst material in the catalytic converter has not reached a sufficient temperature in order to sufficiently process the unwante...

AI Technical Summary

Benefits of technology

It is an object of the present invention to reduce hydrocarbons produced during cold start of a spark ignited internal combustion engine by

employing direct fuel injection to achieve rapid combustion and reduce catalyst warm-up time.

In accordance with the primary object of the invention, in a preferred embodiment, hydrocarbon emissions during cold start are reduced by employing an internal combustion engine which includes fuel injectors positioned to inject fuel directly into combustion chambers of the engine, a high pressure fuel supply pump for pumping fuel to the fuel injectors, and an engine controller for controlling operation of the engine. At engine start, upon initiation of electrical power to the engine, the electronic engine controller allows a predetermined period of time to elapse to allow the high pressure fuel supply pump to reach a predetermined operating pressure. Upon the first engine cycle, for each cylinder of the engine, the quantity of fuel injected into each cylinder and the ignition timing is controlled to achieve combustion in the first engine cycle by injecting a quantity of fuel to compensate for combustion chamber wall wetting effects and to achieve a substantially stoichiometric air / fuel ratio in each combustion chamber, and controlling spark timing according to an empirically determined value which provides the greatest probability for ignition. For a first predetermined number of subsequent engine cycles, the quantity of fuel injected into each cylinder and the spark timing is controlled to rapidly increase the temperature of surfaces of the combustion chambers by injecting a quantity of fuel into each combustion chamber to achieve an air / fuel ratio substantially equal to or marginally leaner than a stoichiometric air / fuel ratio and advancing spark timing in each cylinder by a predetermined number of degrees of crankshaft rotation from a predetermined optimal ignition timing point. For a subsequent, second predetermined number of engine cycles, the quantity of fuel injected into each cylinder and the spark timing is controlled to rapidly increase the temperature of the surfaces of the exhaust system components of the engine, by injecting a first quantity of fuel for each engine cycle during the intake stroke of the engine cycle and injecting a second quantity of fuel later in the same engine cycle during the combustion stroke of the engine cycle, and retarding spark timing for each cylinder from the predetermined optimal ignition timing point.

An advantage of certain preferred embodiments is that combustion is achieved on the first engine cycle, thus reducing the emission of unburned gasoline vapors. Moreover, by controlling the quantity of fuel delivered and the spark timing in a manner to rapidly warm-up the surfaces of the combustion chamber, combustion stability and efficiency is further enhanced, resulting in further reductions of tailpipe emissions of hydrocarbons. Finally, by then controlling the quantity of fuel delivered and the spark timing in a manner to rapidly warm-up the catalytic converter, even further reductions in tailpipe hydrocarbon emissions are achieved without the cost and complexity imposed by additional hardware components such as an electrically heated catalyst.

Problems solved by technology

The temperature of the intake passages and the combustion chambers of the engine during the early stages of a cold start inhibit the proper vaporization of fuel.

As a result, during cold start, a stoichiometric air / fuel ratio is difficult to achieve with intake port fuel injection.

During the early stages of a cold start, the catalyst material in the catalytic converter has not reached a sufficient temperature in order to sufficiently process the unwanted, and uncombusted, by-products of combustion.

Unfortunately, use of the EHC adds additional cost, extra complexity, and requires a delay prior to engine starting to allow the EHC to preheat the catalyst.

However, Sasaki et al. do not contemplate reduction of hydrocarbon emissions by achieving immediate combustion as quickly as possible upon cold start.

Thus, the approach contemplated by Sasaki et al. has limited use in cold start of an engine.

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