GB2183727A - Variable volume pre-chamber diesel engine - Google Patents

Abstract

A diesel engine which has its pre-chamber 1 closed at one end by a piston 4 operated by a cam 11 or an eccentric (12, Figure 8) to reduce its volume after injection of fuel. The pre-chamber lies to one side of the normal diesel engine cylinder and communicates with it by a small passage. Above the pre-chamber and entering into it is the injector. The piston 4 can be stroked to cycle at half crankshaft speed with velocities and events determined by the cam profile. <IMAGE>

Description

SPECIFICATION Variable volume prechamber diesel engine This invention relates to a variable volume prechamber diesel engine.

Background Most diesel engines are divided chambertypes commonly known as indirect injection. A divided combustion chamber is one in which the combustion space is divided into two destinct compartments interconnected with eachother. Between them are restrictions orthroats small enough so that consider- able pressure difference will occurto causeturbulence during combustion process in the main cylinder.

When burning starts, separated from the piston by a throat, proportionate burning takes place from one side to the other. To initiate burning, fuel is sprayed into the prechamberto ignite fuel droplets under high pressure and turbulence but its projection or advancement into the main stream ofthe cylinder relies soley on its inherent expansion.

This is a major difference when compared with direct injection which has its available oxigen in the main cylinderfeeding the flame front produced by spraying directly into the cylinder.

Whilst it is a reliablewayofflamepropagation when comparing indirect with direct injection, but it does sufferfrom heat loss from one chambertothe other and possibly in some cases increases burn time as it relies heavily on flame projection into the main cylinder.

When one considers the combustion volume available over the period of injection time sufficientto produce maximum possible cylinder pressure then the maintenance ofthis pressure is very dependant on piston motion in the cylinderforgood air density to ignitethefuel droplets if complete burn isto be accomplished over effective crankshaft angles. Unfortunately the piston will not wait for complete burn because volume is increasing over the spray crank shaft angle and will inevitably result in reducing air density.

Therefore this investigation reduces volume in crease change overspraycrankshaftangle in order to maintain air density under spray injection. Thus we are not only conserving air density at injection period but also other advantages are realised like im proved exhaust expulsion, for late exhaust valve op ening and the admission of more airfor a given stroke thus improving torque output by careful late exhaust valve opening event.

Therefore the invention that we describe here is typical of what can be achieved by this configuration by the way of an example we show with reference to the accompanying drawing in which; Figure 1 shows end section through engine with details of plunger piston prechamber and its cam ac tion. Note; Piston is shown at T. D. C. whilstthe conrod is at 45 degrees out of position.

Figure2illustratesthe complete cycle stages of combustion cycle.

Figure3shows graphicallythevolume change at injection with volume conservation at complete burn.

Figure 4shows planview of prechamber in relation to cylinder.

Figure 5shows details of prechamber plunger piston with its cam action.

Figure 6 illustrates the cyclic motion of prechamber plunger piston in relation to the main piston with exhaust & inlet valve events.

Figure 7illustrates a conventional engine prechamber.

Figure 8shows an alternative prechamber piston drive action by eccentric.

Variable volume prechamber diesel engine The invention that we describe here in this specification relates two important improvements to an indirect injection diesel engine as used for load carrying vehicles, passenger cars and marine engines.

The improvements described in this specification contain major improvements over existing designs in that its function reduces hydrocarbon exhaust emissions and smoke and in addition improvesthe overal efficiency for improved economy of opperation. This is mainly due to important improvements in the prechamberdesign Figure 1 controlling airde- nsity at spray injection. High air density under spray conditions is essential if good ignition and burn are to be achieved and this invention Figure 1 controls thevolume changeto ensure airdensity is main tained over longer crankshaft anglesthan the normal case.

Essentially these improvements to which we refer consistofthe incorporation of an additional cylinder (1) lying to one side and communicating with the main cylinder (2) but of a smallersize and which is driven by the crankshaft (3). It has a special relation shiptothe crankshaft (3) motion Figure 6 orspeed in each cycle, the small prechamber plunger piston (4) being driven (5) at halfthe speed or motion ofthe main crankshaft (3) driven piston (7) therefore traverses or strokes at half the stroking speed of the main piston (7).

The main piston (7) takes the normal expansion of gasses as with any internal combustion engine but the small prechamber plunger (4) accomplishes a better air pressure or density before and during spray injection and burn.

This ensures better ignition of spray droplets because of volume reduction of the prechamber (1 ) maintaining air density whilst the main cylinder (2) volume is increasing, this also ensures a transfer of burning fuel from the prechamber(1)tothe main cylinder (2) for good air mixing. In the normal case the projection of flame front from the prechamber (9) to the main cylinder (2) relies soley on its inherent expansion in the prechamber (9). This will cause a slight heat loss between the prechamber (9) and the main cylinder (2), in the case of the invention Figure 1 this heat loss is reduced and at the sametimeturbulence is added to the flame projection mechanically into the main cylinder (2).

The action ofthe plunger piston (4) is made by a cam (11) or alternatively an eccentric driven connect ing rod (12) Figure8The cam (11) can be profiled to give different events in opening and closing the prechambervolume (1), thereforethis variable volume prechamber (1) can be cycled for positive effects in addition to that which has been stated. It can also add to displacement volume without increasing crankshaft (3) stroking therefore more air is drawn in improving volumetric efficiency. Also exhaust gas residuals are expulsed by the plunger piston (4) ensuring more air availability on the following induction stroke for improved burn efficiency and less hydrocarbon emission.

Through the effects ofthe plunger piston (4) closing on the exhaust stroke it has a larger displacement volume closing to expulse exhaust gases more rapidly then the conventional case thus permiting thevalvetimingtoclosesoonerforbefteradmission trapping and to close later four exhaust timing to provide cylinder pressure conservancy on the power stroke for more engine torque. All this will give better volumetric and thermal performance by the admission of more air through the displacement of the prechamber piston (4). Thus effectively increasing and decreasing the displacement volume that normally exists in the conventional engine Figure 7.

Claims (9)

1. Adiesel engine which has indirect injection by means of a variable volume prechamber cylinder (1).

The means for varying the prechambervolume (1 ) is by stroking a piston (4) closing one end ofthe prechamber which communicates by a small passage to the main combustion cylinder. The stroking piston is cycled at half the main piston speed but can have various velocities according to the acting cam or eccentric design.

2. A diesel engine as in claim (1 )where its growth of combustion is assisted buy a plunger piston incor porated inthe prechambercylinder pushing flame frontintothe main cylinder.

3. A diesel engine as in claim (1) & (2) wherein the closure ofthe prechambervolume bythe plunger piston maintains air density during the injection spraycrankangle.

4. Adiesel engine as in claim (1) & (2) wherein the closure ofthe prechambervolume by the plunger assists in the flame travel & burn turbulence into the main cylinder.

5. Adiesel engine as in claim (1) & (2) wherein the closure ofthe prechambervolume by the plunger piston expulses exhaust gasses by reducing overal dead volume atthe exhaust stroke.

6. A diesel engine as in claim (5) wherein bythe expulsion of exhaust gasses by the plunger piston allows late exhaust valve event, therefore conserving more cylinder pressure for more torque.

7. A diesel engine as in claim (1) wherein the stroking ofthe plunger piston in the prechamber volume induces more airto be taken in the induction stroke.

8. A diesel engine as in (6) wherein the closure of the prechambervolume by the plunger piston expulses exhaust gas and ensures purer air without exhaust gas residuales to be drawn in for the compression stroke.

9. A diesel engine substantially as described herein with reference to figures 1 to 8 of the accompanying drawings.