Internal-combustion engines – Two-cycle – Rear compression
Patent
1987-03-11
1989-02-28
Myhre, Charles J.
Internal-combustion engines
Two-cycle
Rear compression
123500, F02B 3304
Patent
active
048075728
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the timing of the injection-ignition phase of a spark ignited internal combustion engine where the fuel is injected directly into the combustion chamber of the engine.
In order to obtain the more desirable levels of fuel efficiency and exhaust emission control it is desirable to control the position of the atomised fuel cloud in the combustion chamber. It has been observed that the preferred cloud position is not constant, and particularly varies with engine load, and speed. In two stroke cycle engines the control of the fuel cloud is of particular importance to limit the loss of fuel through the exhaust port which may not be fully closed during at least part of the period of injection of the fuel.
It is understood that under light loads, and hence low fuelling rates, the degree of distribution of the fuel in the cylinder should be restricted to reduce the degree of dilution of the fuel by mixing with the gas in the combustion chamber. The dilution of the fuel gives a lean mixture that is more difficult to ignite, and to maintain combustion until the full fuel charge is burnt. However at high load and high fuelling rate the degree of distribution should be increased to ensure the greater quantity of the fuel has access to sufficient air (oxidant) to achieve combustion of all of the fuel.
It is known to be desirable to establish a stratified fuel charge in the combustion chamber particularly at low engine loads and speeds, so that a fuel rich charge is located in the vicinity of the spark plug. However at low engine speeds there is a time interval between fuel injection and ignition which may permit a wide dispersion of the fuel within the combustion chamber. Further, at high loads at relatively high engine speeds, where dispersion of the fuel is desirable, less time is available between fuel injection and ignition to achieve that dispersion. This problem is aggravated by the fact that it has been commonly believed desirable to commence injection of the fuel after, or only shortly before, exhaust port closure. This practice is based on the belief that earlier injection would result in some of the newly injected fuel being carried out through the exhaust port before it is closed. However such practices are not conductive to achieving the required fuel distribution at low and high engine speeds respectively, and thus contribute to potential incomplete combustion of all the fuel and to resultant undesirable exhaust emissions, particularly hydrocarbons (HC).
It is therefore an object of the present invention to provide a method of operating an engine, particularly a two stroke cycle engine, that will contribute to control of the fuel distribution in the engine combustion chamber in a manner to assist reduction in exhaust emissions.
With this object in view there is provided by one aspect of the present invention, a method of operating a spark ignited two cycle internal combustion engine having a combustion chamber, and an exhaust port opened and closed in time relation to the engine cycle to control the exhausting of gases from the combustion chamber, said method comprising, injecting a metered quantity of fuel directly into the combustion chamber so that at low engine loads and speeds at least 80% of the metered quantity of fuel is delivered into the combustion chamber after the exhaust port has closed, and at least at some high engine loads of at least 80% of the metered quantity of fuel is delivered to the combustion chamber before the exhaust port is closed.
The timing of the fuel injection so that the fuel is injected later in the compression stroke, after exhaust port closure, results in a short time being available for the fuel to disperse within the combustion chamber. This is desirable at low engine loads, and particularly at low engine loads and speeds. Also the injection of the fuel after exhaust port closure means that there is somewhat less movement of the gases in the combustion chamber, which also contributes to limiting fuel dispersion. Naturally escape of fuel through
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Myhre Charles J.
Okonsky David A.
Orbital Engine Company Proprietary Limited
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