GB2337558A

GB2337558A - Compression ignition engine particulate reduction

Info

Publication number: GB2337558A
Application number: GB9910856A
Authority: GB
Inventors: John Heath Greenhough
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-05-16
Filing date: 1999-05-10
Publication date: 1999-11-24
Also published as: GB9810475D0; GB9910856D0

Abstract

Over a lower part of the power range up to a transition temperature engine power is varied by varying the quantity of the main injection and thereafter the main injection of fuel is supplemented by a secondary introduction of Butane gas which is introduced early in the induction stroke when the cylinder temperature has been elevated to 950‹C by the throttling of the exhaust gas. This is the transition point that will propagate Butane flame when ignited simultaneously with the main injection of fuel.

Description

0 1 - compression Ignition Encrine 2337558 This invention relates to the

delivery of fuel to the.compression Ignition engine.

The health hazard of air-borne carbon particles in exhaust fumes may be responsible for many deaths In towns and cities.

These small particles hhat come mostly from the exhaust pipes of diesel taxis, lorries and buses are called PM 10 because each particle Is less than hen micrometres across.

The health hazard of carbon particles has led to the drafting of stringent regulations for the reduction of particles in new diesel engines, but this requirement does hot apply to the thousands of older vehicles that are responsible for 90% of the present problem.

Although 1 have disclosed in my previous patents GB 2169960 and GB 2277776 a method for the reduction of pollution for old and new diesel engines this method requires additional engineering work to be undertaken tor the vaporization and Introduction of a measured amount of a diesel fuel Into Ehe air-intake of the engine.

Because of the additional cosh and there Is no requirement In law, this has deterred many fleet owhers and taxi managers from carrying out the necessary modif Icablon ho reduce pollution.

It is the object of the present invention to remove 80% of particulate matter from exhaust gases of old vehicles without the cost of engine modification.

The use of gas ds a fuel In the Internal combustion engine is well known. The common gases used are methane, compressed natural gas, liquid petroleum gas (LPG).and propane. All these gases have high octane numbers.

Methane has an octane number of 120 and propane has an octane number of 112. This gives them a high resistance to chemical reaction and heat release under compression. This makes these gases Ideal fuels for the premixed spark ignited engine cycle because of their resistance to compression ignition at high compression ratios.

1.

These gases can also be used as a pre-mixed engine fuel with a high compression ratio.A small amount of diesel fuel can be injected at the end of the compression stroke to ignite the pre-mixed charge instead of spark ignition.

Although Butane gas can be used as a pre-mixed spark ignited fuel it is not recommended because It has an octane number of approximately 20% lower than that of propane and will spontaneously ignite at a temperature 1000c lower than propane when subjected to high compression In the engine cycle.

3 The problem in the diesel engine is created by the method of combustion. This is because the time available for mixing the liquid fuel and air is so short that complete combustion is difficult to achievL,. This causes the release of minute particles of unburned carbon (PM10s) into the atmosphere.

The amount of particulate matter released increases in proportion to the speed and load. The speed of mixing and burning is controlled by the fuel's ability to penetrate the combustion gas residue left behind by the combustion that has already taken place.

This becomes more difficult as the rate of injection increases. The problem of high-load fuel penetration is substantially reduced by introducing part of the fuel as a pre-mixed charge.

Particulate matter can also be increased when the temperature of the cylinder is reduced. The temperature of the combustion chamber is in proportion to the amount of fuel burnt.

This means that as soon as the amount of fuel is reduced the temperature drops. This applies at tick-over and low load operation. At tick-over the quantity of fuel injected into the cylinder is so small that combustion will only take place in the area around the injector nozzle. This causes a big reduction in the overall cylinder temperature.

At idle the combustion can take place at very low temperature owing to the chilling of the combustion flame on cool cylinder surfaces. This will cause an increase in particulates and a pungent odour from the exhaust.

4 - Although re-circulated exhaust gas (EGR) can be used to improve emissions the exhaust gas temperature is too low to increase cylinder temperature sufficiently to overcome low temperature pollution.

To overcome this problem a throttle valve can be incorporated in the exhaust pipe to increase engine back pressure. This retains a high proportion of the hot combustion gases in the cylinder and also reduces the amount of cool air entering the cylinder during the induction stroke.

When the engine is accelerated from tick-over to maximum load the quantity of fuel injected will reduce the cylinder temperature by about 1000C.

This will have a considerable affect on combustion. This is because more heat is absorbed to achieve flammable combustion. The lowering of the speed of combustion causes the last part of the fuel injected to burn too late in the engine cycle for combustion to be completed.

This causes the smoke problem that is associated with the diesel engine when the accelerator is fully opened.

When Butane gas is mixed with air thermo chemical reaction takes place when subjected to heat and pressure. This reaction may be small or high depending on the amount of gas in the cylinder and the pressure applied.

When Butane gas is added as a secondary charge of fuel into the cylinder of the engine during the induction stroke it is too lean to cause premature ignition.

During the compression stroke of the engine there is a high rate of thermo chemical heating (pre flame reaction). This release of extra heat during compression speeds up spontaneous ignition of the main charge thereby compensating for the increased delay caused by the reduced temperature associated with acceleration from low load.

It is the object of the present invention to use an exhaust throttle valve and Butane gas to substantially reduce carbon particulates from the exhaust gas of the diesel engine.

A bottle of Butane gas is located at an appropriate position on the vehicle connected with a pipe to supply gas to the air intake of the engine. A valve is located in the pipeline to switch the gas on when the engine is accelerated and off when the accelerator is released.

In my previous patent I have disclosed a threshold temperature that must be achieved in the diesel engine cylinder before any pre-mixed fuel added to the engine will propogate flame. This temperature referred to as the transition point is governed by the amount of fuel directly injected into the cylinder.

The on and off position of the gas valve can be adjusted to coincide with the activation of the accelerator so that gas will not enter the"cylinder until the transition point is reached.

Under the standard diesel engine operation a minimum of 30 - 35% of the main fuel charge will be required to be injected directly into the cylinder before the transition temperature is reached.

6 To overcome this problem a throttle valve is placed in the exhaust pipe to restrict cool air intake and retain hot gases in the cylinder.

The on/off position of the exhaust throttle valve and gas supply valve can be adjusted to coincide with the activation of the accelerator so that the throttle valve will restrict the exhaust gas flow until the temperature in the cylinder is high enough to propogate Butane gas flame.

At this point the gas valve is activated and the secondary charge of Butane gas is introduced into the air supply of the engine and at the same time the exhaust gas throttle valve is progressively opened.

When the gas valve is activated the amount of gas entering the cylinder can be varied from 0% to 30% of the total fuel added.

The invention provides a method of operating a compression ignition internal combustion engine which is provided with means for injecting fuel into the cylinder during a compression stroke, wherein over a lower part of the power range from tick-over up to a transition point, engine power is varied by varying the quantity of the main injection late in the compression stroke from a minimum.at tick-over up to a higher value at the transition point, and wherein over a higher part of the power range from the transition point up to full power, the main injection of fuel is supplemented by a secondary introduction of Butane gas which is initiated earlier in the induction stroke.

7 When the cylinder temperature has been elevated by the throttling of the exhaust gas to a temperature that will propogate flame when ignited simultaneously with the main injection of fuel.

The invention will be described further by way of example with reference to the accompanying drawings.

Figure 1 is a set of diagrams illustrating operation of a conventional compression ignition engine.

Figure 2 is a similar set of a first preferred engine of the invention.

Figure 3 is a similar set for a second preferred engine of the Invention.

Figure 4 is a similar set of drawings as illustrated In Fig. 2 and 3 but with the addition of an exhaust throttle valve.

In each of the sets of diagrams Illustrated In Fig. l, 2 and 3 T.D.C. indicates top dead centre in the cylinder of a reciprocating piston engine, other angles being given in relation to T.D.C.

A main injection of fuel is indicated by narrow cross hatching and in figures 2 and 3 the introduction of Butane gas is indicated by wider cross hatching. S.T.O. is used as an abbreviation for stoichiornetric. In each set of diagrams the left hand diagram 'A' illustrates low power (tick-over) and the right hand diagram 'Cl indicates full power. In each case diagra'm 'B' indicates a transition point.

8 In the conventional compression ignition engine using diesel fuel illustrated in figure 1 there is a single main injection of fuel which usually commences at or about 20 degrees before T.D.C.

At this point the cylinder is hot enough to initiate ignition of the injected fuel and the combustion starts shortly after injection commences and finishes shortly after injection ceases. At full power injection may continue up to or beyond T.D.C. 70% S.T.O. tends to be a maximum value, higher values causing a smoky exhaust. The diagrams are drawn to illustrate progressively longer periods of injection from low to high power consistent with an injector construction and size wherein the rate of injection is varying the period of operation of the injector. This is in accordance with conventional practice.

The engine whose characteristics are shown in Figure 2 operates in an identical manner to the Figure 1 engine over a lower part of its power range from 'A' to 'B' The transition point 'B' is chosen to occur at that position wherein after combustion of the main fuel portion the temperature within the cylinder is everywhere greater than 950 degrees.

In the conventional engine cycle as illustrated in Fig. 1 35% of the main fuel charge is required before the transition temperature 950c is reached. This will have a detrimental affect on particulate emissions.

9 In the engine of the invention a throttle valve is placed in the exhaust pipe to increase engine back pressure. This retains hot gases in the cylinder and restricts the cool air intake. This retains the heat in the cylinder at tick-over and low load.

By this method of operation the transition temperature can be achieved when the main injection of fuel reaches 20 - 25%. This is illustrated at point 'B' in Fig. 2.

Above the transition point 'B, in Fig.2 up to a maximum power (diagram C) the quantity of the main fuel injected is progressively increased. This corresponds with a fuel injection rate of 60% S.T.O.

This increase is less than would occur with the conventional engine (Fig. 1). From the point 'B' upwards in the power range Butane gas is added to the inlet air this takes place before the main injection and with air in the cylinder forms a mixture which is ignited upon ignition of the main injected fuel.

The quantity of Butane gas in Fig.2 is held at about 10% S.T.O. Because the secondary charge is pre-mixed it is possible to achieve full power that consists of 60% S.T.O. main and 10% S.T.O. secondary fuel to achieve a 70% S.T.O. fuel injection as in Figure 1.

The secondary injection of Butane gas in the figure 2 engine is timed to coincide with the commencement of the induction stroke when more time is available for mixing with the air entering the cylinder.

- 10 Although the Butane gas is too lean to cause premature ignition during the compression stroke there will be thermo-chemical heating (pre-flame reaction).

This release of extra heat makes up for the reduction in temperature caused by the main injected fuel under maximum acceleration.

In the engine illustrated in figure 3 the same procedure applies as in figure 2.

Diagram W illustrates tick-over, diagram 'B' the transition point, diagram C, injection of 40% S.T.O. main fuel and 30% S.T.O. Butane gas.

Because the secondary charge is pre-mixed it is possible to achieve full power that consists of 40% S.T.O. main fuel and 30% S.T.O. Butane gas to achieve a 70% fuel charge as in figure 1, without releasing excessive carbon particles into the atmosphere.

Figure 4 is a similar set of drawings as in Fig. 3 but with the addition of an exhaust gas throttle valve.

The diagrams are drawn to illustrate progressively longer periods of injection from low to high power. This represents the opening of the accelerator. Diagrams W and 'All represent tick-over. Diagrams 'B' and 1B11 represent the transition point where Butane gas is added. Diagrams 'C, and 'Cl' represent maximum power.

11 In the diagrams 'All, 1B11 and 'Cl' T is a throttle plate in the exhaust pipe which is opened and closed by the activation of Lever L when the engine is accelerated and closed when the accelerator is released.

At tick-over or low load the throttle plate T in diagram All is held at a position that will only allow sufficient exhaust gas to be released to maintain tick-over.

Under acceleration the throttle plate is progressively opened until it reaches its maximum diagram 'Cl, Although the method described substantially reduces carbon particles from the exhaust of the diesel engine it also reduces NOX.

It will be understood that the conditions described are by way of example only and can be varied depending on the compression ratio or the addition of turbocharging so that the quantity of secondary fuel added can be infinitely variable and need to be selected for different engine operating conditions.

The invention can be applied to a four stroke engine, a two stroke engine or a rotary engine.

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Claims

Claims

A method of operating a compression ignition internal combustion engine which includes a cylinder whose volume varied cyclically and which is provided with means for injecting a hydrocarbon fuel into the cylinder, wherein over a lower part of the power range thereof from tick-over up to a transition point, engine power is varied by varying the quantity of the main injection late in the compression stroke from a minimum at tick-over up to a higher value at the transition point, and wherein over a higher part of the power range from the transition point up to full power. The main injection of fuel is supplemented by a secondary introduction of Butane gas which is initiated earlier in the engine cycle and which mixes with air in the cylinder to form a combustible mixture which is ignited simultaneously with the main injection of fuel when the cylinder temperature has been elevated to 9500C by the throttling of the exhaust gases.

Y
2. A method as claimed in Claim 1 wherein the exhaust throttle valve is activated by the accelerator.
3. A method as claimed in Claim 2 wherein the exhaust throttle valve is controlled by a thermostat.
1 13 A method as claimed in Claim 3 wherein the exhaust throttle valve is activated electronically.
5.

A method as claimed in Claim 4 wherein the exhaust throttle valve is progressively opened when the cylinder temperature exceeds 9500C.
A method as claimed in any preceding claim wherein Butane gas is introduced into the cylinder when the temperature is at or above 9500C.
A method as claimed in Claim 1 wherein over the higher part of the power range the quantity of the main fuel charge remains constant, the quantity of Butane gas being progressively increased.
8. A method as claimed in Claim 7 wherein over the higher part of the power range the quantity of fuel introduced by the main injection increases progressively.
9.

An internal combustion engine including a cylinder whose volume varies cyclically and which has means for injecting a hydrocarbon fuel into the cylinder during a compresion stroke, control means being provided and connected between a power control of the engine, said means for injecting and a secondary fuel introduction means, said control means being operative to control the engine in accordance with the method of any preceding claim.
10. An internal combustion engine substantially as hereinbefore described with reference to and as illustrated in Fig. 2, 3 or 4 of the accompanying drawings.