Method of injection of a fuel-gas mixture to an engine

Details Method of injection of a fuel-gas mixture to an engine Method of injection of a fuel-gas mixture to an engine

2000-06-01

2003-05-20

Yuen, Henry C. (Department: 3747)

Internal-combustion engines

Combustion chamber means having fuel injection only

Using multiple injectors or injections

C123S525000, C123S531000

Reexamination Certificate

active

06564770

ABSTRACT:

This invention relates to fuelling of engines by injection of fuel-gas mixtures to combustion chambers of the internal combustion engines typically operating on either the two or four stroke cycle.
The advantages in terms of low emissions in exhaust gases from internal combustion engines having combustion chambers or cylinders directly injected with fuel-gas mixtures are recognised and result from better control over fuel distributions and quantities than are possible in carburetted engines, in addition to other factors.
In this respect, it has been disclosed by the Applicant in, for example, U.S. Pat. No. 4,800,862 that, in efforts to control the harmful components in the exhaust gases from engines, control of the fuel distribution in the combustion chamber(s) of the engine may be beneficial. Accordingly, that patent discloses, in particular regard to a dual fluid fuel injection system wherein a gas under pressure is used to entrain and deliver a separately metered quantity of fuel to an engine, control over the introduction of fuel to the gas to obtain a predetermined fuel distribution in the combustion chamber(s) of the engine at the time of ignition. In particular, it is described as most desirable in a spark ignition engine that the predetermined fuel distribution involve a relatively fuel rich mixture in proximity to the ignition means at the time of ignition.
Typically, the ignition means is located in the cylinder head of the engine and accordingly, at ignition, a fuel rich region is desirably formed in this area of the cylinder. In certain engines, typically those having centrally mounted direct injection systems, this is accompanied by an adjacent increase in the air/fuel ratio of the remaining combustion charge in the axial direction of the cylinder (ie. becomes leaner). Such a combustion charge is said to be of stratified type and has recognised advantages at ignition, particularly under low load conditions. Low load conditions may be generally described as a load less than 25% of the maximum load achievable at a particular engine speed.
Typically, the preferred fuel distribution in the cylinder will vary with the engine load and speed and so, as described in the Applicant's U.S. Pat. No. 4,800,862, the rate of introduction of the determined quantities of fuel to the cylinder(s) of the engine is controlled to achieve the most efficient distribution for particular engine operating conditions. Therefore, at high loads it is often more important to have a substantially uniform air/fuel ratio throughout the cylinder such that the fuel is exposed to sufficient air to combust all of the fuel resident within the cylinder. High load may generally be defined as load greater than 75% of the maximum load achievable at a particular engine speed.
It is an object of the present invention to provide a method of fuelling an internal combustion engine which enables efficient operation of the engine with In acceptably low emissions of NO
x
, hydrocarbons and other pollutants associated with inefficient engine operation.
With this object in view, the present invention provides a method of fuelling an internal combustion engine by injection of a fuel—gas mixture to a combustion chamber of the engine comprising delivering a metered quantity of fuel from a fuel metering means to a delivery injector, the delivery injector being in communication with both the combustion chamber and a supply of pressurised gas for effecting delivery of the metered quantity of fuel to the combustion chamber, wherein at least one of the fuel metering means and the delivery injector are controlled in multiple events and a predetermined fuel distribution is obtained in the combustion chamber at ignition.
The multiple events may occur during a cycle of engine operation to obtain a predetermined fuel distribution in the combustion chamber at ignition during that cycle of engine operation. The fuel metering means may be controlled to effect a single pulse of controlled duration for providing a metered quantity of fuel to the delivery injector. Such a pulse or controlled opening of the fuel metering means may be described as a “fuel metering event”.
The metered quantity of fuel is then delivered entrained in pressurised gas to the combustion chamber by opening of the delivery injector, wherein such a pulse or opening of the delivery injector may be described as a “gas supply event”. The delivery injector may desirably be controlled to effect a plurality of gas supply events which carry fuel directly into the cylinder or combustion chamber of the engine. The delivery injector may be controlled to effect a plurality of pulses of controlled duration during a single cylinder cycle to deliver the metered quantity of fuel to the engine and to, on occasion, enable a desired engine control strategy to be effected. A cylinder cycle may be defined by that period of piston reciprocation between top dead centre and subsequent return to top dead centre. More compendiously, a cylinder cycle may be measured by that period between the piston having any position in the cylinder and subsequent return to that position. Thus, a repeatable sequence of events may occur over a number of cylinder cycles. The sequence of fuel metering and gas supply events is typically contoured over the 360° or 720° period, depending on whether the engine is to operate on the two or four stroke cycle. Thus, where some of the events in a sequence occur after top dead centre they may be considered to occur during the same cylinder cycle as an earlier such metering or gas supply event that occurred before top dead centre.
The fuel metering means is conveniently in the form of a fuel metering injector and supply of pressurised gas to the delivery injector is typically via a duct or passage communicating the supply of pressurised gas, typically an air compressor, with a holding chamber of the delivery injector. The holding chamber may remain pressurised at all times during engine operation and is preferably selectively communicated directly with the combustion chamber during the plurality of gas or air supply events each cylinder cycle.
In this respect, the method of the present invention may be implemented in a number of ways with the timings of opening/closing of the fuel metering and fuel delivery injectors, otherwise described respectively as the fuel metering and gas supply events, being controllably timed relative to ignition timing, and each other, by the control unit for the engine, typically an electronic control unit. The timing and/or duration of the fuel metering and/or gas supply events may be made a function of engine speed or engine load or both. Further, the fuel metering and gas supply events may in certain applications be overlapped.
While any number of gas or air supply events in the cylinder cycle could be arranged in excess of one, a typical number would be two per cycle. The metered quantity of fuel may be delivered to the delivery injector by the fuel metering means in a fuel metering event timed at any time in the cylinder cycle relative to the gas supply events. For example, initiation of a first gas supply event may enable delivery to the combustion chamber of a portion, desirably a major proportion, of a metered fuel requirement for the engine per cylinder cycle under particular engine operating conditions. Some time later, but during the same cylinder cycle, a second gas or air supply event may deliver any remaining portion of the previously metered fuel amount to the combustion chamber. In some situations, this second air supply event may be initiated to scavenge any “hang-up” fuel remaining within the fuel delivery injector. It may be initiated either in association with an ignition event or not as desired. That is, a typical delivery injector has a holding chamber or bore through which fuel passes or is retained. A film of fuel may adhere to the walls of the chamber or bore following the first air event due to surface tension effects and it is this phenomenon that is referred to as fuel “hang-up” or “hang-up” fuel.
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