GB2468872A

GB2468872A - Method of Operating a Compression Ignition Engine by Altering the Fuel Injection Timing Based on Sensed Engine Parameters.

Info

Publication number: GB2468872A
Application number: GB0905049A
Authority: GB
Inventors: Robert Womersley
Original assignee: JC Bamford Excavators Ltd
Current assignee: JC Bamford Excavators Ltd
Priority date: 2009-03-25
Filing date: 2009-03-25
Publication date: 2010-09-29
Anticipated expiration: 2029-03-25
Also published as: EP2236796A2; EP2236796A3; GB2468872B; EP2236796B1; US20100242913A1; GB0905049D0; US8706380B2

Abstract

A method and apparatus of operating a compression ignition or diesel engine 10, the method includes sensing an engine temperature or a temperature associated with the engine with a first sensor S1, and providing an input to a controller 31, the controller operates a fuel injection pump 28 to deliver fuel to the engine according to a first timing regime when the sensed temperature is above a threshold temperature, and according to a second, advanced timing regime when the sensed temperature is below the threshold temperature. The method further includes sensing with a second sensor S2 a combustion chamber pressure and when the controller operates the fuel injection pump according to the second timing regime and the sensed pressure exceeds a threshold which indicates that the combustion chambers are operating above a desired maximum pressure, the fuel injection pump changes from the second, advanced timing regime to the first timing regime. The pressure sensor S2 may sense the actual pressure within the combustion chamber or a parameter which is indicative of the combustion chamber pressure such as exhaust gas pressure or the intake air pressure in the case of a turbocharged engine. The method is particularly aimed at preventing a maximum cylinder pressure being exceeded when the engine is initially started from cold and is particularly suitable for use on a diesel engine driving a generator that operates at a generally constant load.

Description

Title: Method of Operating a Compression Ignition Engine

Description of Invention

This invention relates to a method of operating a compression ignition engine such as a diesel engine, and more particularly to a method of operating a compression ignition engine in which fuel is delivered to the or each combustion chamber of the engine by a mechanically operated fuel injection pump apparatus.

A mechanically operated fuel injection pump apparatus is typically driven by the engine, e.g. by the engine crankshaft, and includes one or more pumping chambers from which fuel is distributed for feeding directly into the or each combustion chamber by a or a respective injector, or indirectly, into a or a respective charge air airway or manifold, by an injector so that the fuel is mixed with the air in the combustion chamber or chambers. Fuel typically is injected into the or each combustion chambers directly or indirectly, prior to the piston in the combustion chamber reaching top dead centre (TDC), and typically the fuel will be ignited prior to the TDC piston position. Fuel may continue to be delivered to the combustion chamber as the piston moves away from TDC.

The fuel injector pump apparatus is operated to deliver to the or each combustion chamber a metered volume of fuel in accordance with demand set by an engine governor, and according to a timing regime i.e. at a selected crank angle before TDC when fuel injection commences and after TDC when fuel injection ceases, which volume of fuel and timing regime is generally arranged to ensure maximum fuel combustion and engine economy, and minimum emissions. * 2

It is known that in normal use of the engine, when the temperature of the engine is raised to a normal operating temperature, a different fuel injection timing regime is desirable compared to when the engine is cold, i.e. on start up. Accordingly it is known to operate the fuel injection pump apparatus according to a different, advanced timing, regime during engine start up, to ensure fuel is provided in the or each combustion chamber earlier in the combustion cycle, i.e. earlier before combustion is initiated in the combustion chamber, which is earlier before the piston reaches TDC that is, at an advanced crank angle than would normally be the case.

In one kind of fuel injector pump apparatus, the timing regime is changed to a cold starting timing regime by operation of a solenoid by an engine controller, which controller responds to a sensed temperature, being the engine temperature or a temperature associated with the engine temperature, when below a threshold temperature.

The solenoid may move a timing component of the fuel injection pump apparatus which advances the onset of fuel injection in each combustion cycle until the sensed temperature reaches the threshold temperature, when the solenoid is de-energised and the timing component of the fuel injection pump apparatus moves back to a normal operating position so that the onset of fuel injection returns to a normal non-advanced regime.

It will be appreciated that when the fuel injection timing regime is advanced in response to the engine controller, when the sensed engine temperature is below the threshold temperature, because fuel will have been provided in the combustion chamber earlier, when combustion commences in each combustion chamber cycle, there will be a surge in pressure in the combustion chamber. * 3

As the torque developed by the engine increases, e.g. engine load increases, the maximum combustion chamber pressure in each operating cycle will commensurately increase.

For a particular engine which may have been designed according to certain engine parameters and/or operated according to design parameters, the design will have a maximum working combustion chamber design pressure which may be greater than any anticipated surge pressure experienced in the or a combustion chamber as a result of operating the engine according to an advanced timing regime.

However, commonly, basic engine designs are modified or their operation is modified, to permit the same basic engine design (i.e. using the same conversion hardware, i.e. engine i.e. the piston(s), rod(s), bearings, head gasket etc.) to be used for alternative applications. For example an engine may be modified or the engine's operation may be modified, in such a way that the maximum combustion chamber pressure is increased, closer towards the maximum design pressure. In such case, any surge in pressure as a result of the fuel injection timing being advanced, could result in maximum pressures in the or a combustion chamber which are not optimal for the engine design.

Moreover, such excess pressure will act on the conversion hardware of the engine (which may not be modified for the modified engine design or operation), and at least as the engine torque develops, the excess pressure could result in damage or at least premature wear to the conversion hardware of the engine.

According to a first aspect of the invention we provide a method of operating a compression ignition engine which includes at least one combustion chamber containing a piston, to which combustion chamber is delivered fuel by a * 4 mechanically operated fuel injection pump apparatus, the method including sensing the engine temperature or a temperature associated with the engine with a first sensor, and providing an input to a controller, the controller operating the fuel injection pump apparatus to deliver fuel to the or each of the combustion chambers according to a first timing regime when the sensed temperature is above a threshold temperature, and according to a second, advanced timing, regime when the sensed temperature is below the threshold temperature, the method further including sensing with a second sensor the pressure in the or at least one of the combustion chambers or a parameter which is indicative of the pressure in the or each of the combustion chambers, and when the controller is operating the fuel injection pump apparatus according to the second timing regime and the sensed pressure or parameter exceeds a threshold which indicates a pressure in the or each of the combustion chambers above a desired pressure, the method including changing operation of the fuel injection pump apparatus from the second to the first timing regime.

Thus by virtue of the invention, the likelihood of a surge in pressure in the or each combustion chamber during start-up of the engine leading to engine damage, e.g. of conversion components is alleviated, as a first, normal, timing regime will be employed when too high a pressure is indicated in the engine, notwithstanding that the engine temperature may be below the threshold temperature.

Engine controllers are known which respond to several different sensors to control combustion to ensure the engine operates normally with maximum efficiency and lowest emissions, including temperature and pressure sensors.

However the present invention ensures that the pressure in the or each combustion chambers is controlled during start-up as the engine warms, to be lower than that which could damage the engine, i.e. a desirable pressure, by * 5 changing from the second, advanced timing, regime to the first, normal, timing regime in anticipation.

Although the pressure actually in the or one of the combustion chambers may be sensed, directly, practically in a production engine this adds unwarranted complexity and cost. Desirably, a pressure is sensed which is indicative of the pressure in the combustion chamber or each of the combustion chambers, e.g. a pressure which is dependent upon the maximum pressure being experienced in a or the or each of the combustion chambers.

In one example, the engine is turbocharged, with the exhaust gases acting on a turbine which drives a compressor to pressurise charge air which is introduced into the or each combustion chamber for combustion. The second sensor may sense the pressure of the exhaust gases, for example in an exhaust gas manifold, or preferably the pressure of the pressurised air. For example, the pressurised charge air may pass through a charge cooler to cool the pressurised charge air prior to the charge air being introduced into the or a combustion chamber, and the second sensor may sense the pressure of the charge air between the compressor and the charge air cooler, which will vary depending upon the pressure in the combustion chamber or chambers.

The fuel injection pump apparatus may include an actuator, such as a solenoid, which responds to a control signal from the controller, to move a timing component of the fuel injection pump apparatus to a position where the onset of fuel injection in each combustion cycle is advanced, usually until the sensed temperature reaches the threshold temperature, or in accordance with the invention, until the threshold pressure or other parameter is sensed by the second, pressure sensor, upon which the solenoid or other actuator is de-energised, or otherwise moves the timing component or permits the timing * 6 component to move back, to a normal position so that the onset of fuel injection returns to a normal non-advanced, first, timing regime.

Because of the inherent layout of mechanical fuel injection pumps apparatus, that is rotary mechanical fuel injection pump apparatus, injection timing may advance naturally with increasing load. Hence whereas there is a high propensity of cold misfire in light load conditions (hence the reason for advancing the timing at low temperatures) this is a substantially reduced risk at higher loads. Thus the timing regime can safely be changed from the second, advanced timing, regime to the first timing regime at higher loads. The method may include changing operation of the fuel injection pump apparatus from the second to the first timing regime when the sensed pressure or other parameter indicates that the pressure in the combustion chamber or chambers is significantly lower than the maximum design pressure of the engine at which damage to the engine may occur.

The invention has particular applicability where the engine is used to drive a generator, when the engine will normally be operated at a generally constant load (speed). Thus the engine may be of the fixed speed-governor kind.

Advancing the timing upon cold starting facilitates start-up as the torque developed by the engine increases towards a design working torque.

According to a second aspect of the invention we provide an apparatus including an electrical generator and an engine to drive the generator, the engine including at least one combustion chamber containing a piston, to which combustion chamber is delivered fuel by a mechanically operated fuel injection pump apparatus, there being a first sensor to sense the engine temperature or a temperature associated with the engine and to provide an input to a controller, the fuel injection pump apparatus being operable by the controller to deliver fuel to the or each of the combustion chambers according * 7 to a first timing regime when the sensed temperature is above a threshold temperature, and according to a second, advanced timing, regime when the sensed temperature is below the threshold temperature, and there being a second sensor to sense the pressure in the or at least one of the combustion chambers or a parameter which is indicative of the pressure in the or each of the combustion chambers, and the controller, when operating the fuel injection pump apparatus according to the second advanced timing, regime, upon the second sensor sensing a threshold pressure or other parameter threshold, which indicates a pressure in the or each of the combustion chambers above a desired pressure, changing operation of the fuel injection pump apparatus from the second to the first timing regime.

Embodiments of the invention will now be described with reference to the accompanying drawings in which:-FIGURE 1 is a diagrammatic view of an engine which is operated by the method the invention; FIGURE 2 is a graph illustrating varying pressure in a combustion chamber as the engine crank turns; FIGURE 3 is a graph plotting increasing engine load (developed torque) against the maximum pressure in the combustion chamber or chambers of the engine of figure 1 at constant engine speed, both where the invention is employed, and if the invention is not employed, as the engine warms up.

Referring to figure 1 a compression ignition engine 10 includes an engine block assembly 11 including a crank case (not shown) which houses a crankshaft C, a plurality of combustion chambers (four in the example -not shown) which each have a piston (not shown) reciprocal therein, the pistons being connected to crankshaft C via connecting rods (not shown). * 8

In use, fuel is injected either directly into each combustion chamber, or indirectly into a respective charge air airstream leading to the or a respective combustion chamber.

The engine 10 in the example is turbocharged, i.e. exhaust gases fed to a manifold 15 act on a turbine 16 to turn the turbine 16, and hence a shaft 17 on which the turbine 16 is provided, before the exhausted gases are exhausted.

Some of the exhaust gases may be fed back to an air intake 19 for introduction back into the combustion chambers with charge air.

Mounted on the shaft 17 is a compressor 20 which is turned as the exhaust gases turn the turbine 16. The compressor 20 compresses ambient air from an air inlet 22 to pressurise the air which is then provided to the air intake 19 for providing as pressurised charge air for combustion in the combustion chambers of the engine 10 together with the fuel.

In the example indicated, the pressurised air from the compressor 20, prior to providing the air to the air intake 19, is cooled in a charge cooler 25.

Fuel for injecting into the combustion chambers of the engine 10 is pressurised by a mechanically driven fuel injection pump apparatus 28 which is shown attached to the engine 10 block assembly 11. The fuel injection pump apparatus 28 is driven from the crankshaft of the engine 10 and in the example is of the rotary kind which delivers a metered volume of fuel (the volume depending upon the setting of an engine 10 governor) towards each of the combustion chambers of the engine 10, and the metered volume of fuel is then injected into the combustion chambers at an appropriate time, for combustion with the charge air. * 9

Referring also to figure 2, as the crankshaft C of the engine 10 rotates, the piston in each combustion chamber will reciprocate. Figure 2 illustrates the changing pressure P in one of the combustion chambers. The TDC position of the piston is indicated. It can be seen that as the piston approaches TDC, in the region indicated at A, in the absence of fuel combustion, the pressure in the combustion chamber will build to a maximum pressure P1, and then as the piston moves away from TDC as the crankshaft continues to rotate, the pressure will ebb. Figure 2 illustrates that in normal use, when the engine 10 is warm and operating for example in a steady state, fuel is injected into the combustion chamber at the position indicated at P2, several degrees of crankshaft rotation before the piston reaches TDC. At this point P2 the temperature of the charge air compressed by the piston in the combustion chamber may already be above the flashpoint of the fuel, so that the fuel immediately commences combustion.

Fuel continues to be injected (and combust) until after the piston passes TDC, prior to the exhaust past valve of the combustion chamber opening.

The area indicated at B indicates the extra pressure (energy) in the combustion chamber due to the combustion of the fuel.

Upon start up of the engine 10 when the engine 10 is cold i.e. below its normal operating temperature, it is desirable to commence injection of the fuel earlier in the combustion cycle, for example at the position indicted at P3. This lessens the possibility of misfiring as the engine 10 warms. The risk of misfiring decreases as engine 10 bad increases as wifl be explained in more detail below.

To commence injection of the fuel to each of the combustion chambers respectively earlier than point P2 in each combustion chamber operating cycle, O 10 a timing component of the fuel injection pump apparatus 28 e.g. a timing ring, is moved by an actuator, which is indicated at 30 in figure 1 and is typically a solenoid 30. The solenoid 30 or other actuator is controlled by an engine controller 31 to move the timing component to advance the timing i.e. to bring forward the point at which is fuel injected to the respective combustion chamber, to point P3, when the engine 10 temperature or temperature associated with the engine temperature, is cold.

In figure 1 a first temperature, sensor is shown illustratively at Si. Typically this will sense the temperature of an engine 10 (liquid) coolant, but may sense lubricating oil temperature, or the temperature of the engine block assembly 11 itself. In each case the first sensor Si provides an input to the controller 31.

When it is determined that the sensed temperature has reached a threshold temperature, being or corresponding to an engine temperature of say, 55°C, the controller 31 controls the solenoid 30 to move the timing component back, or to allow the timing component to move back, to a position in which fuel is injected according to a normal timing regime, i.e. at point P2 for each combustion chamber operating cycle.

For example, the timing component which is moved by the solenoid 30 to advance the timing, may be spring biased to its normal timing regime position.

The controller 31 may signal the solenoid 30 to move the timing component against the spring bias to advance the timing by providing an "on" signal, and the controller 31 may signal the solenoid 30 to allow the timing component to move back to its normal timing regime position by ceasing to provide the "on" signal.

In each case, in normal operation of the fuel injection pump apparatus 28, when the engine 10 temperature is determined to be sufficient, i.e. the sensed temperature is near the threshold temperature, e.g. the normal operating * 11 temperature of the engine 10, the fuel injection pump apparatus 28 operates according to a first, normal timing regime, and when advanced fuel injection is required, at lower engine 10 temperatures, the fuel injection pump apparatus 28 operates according to a second, advanced timing, regime.

Referring again to figure 2, it can be appreciated that when fuel injection timing is advanced, because more fuel is present in the combustion chamber as the piston approaches TDC, there is likely to be a surge of pressure P in the combustion chamber, as suggested at D, as TDC is approached, as the extra fuel ignites, and earlier than normal.

Referring to the graph of figure 3, the maximum pressure PMax in the combustion chamber as the engine 10 load increases, is plotted along the "y" axis for a typical engine 10. The engine 10 load is indicated along the "x" axis in terms of the torque developed by the engine 10, as loads are imposed..

The full line (ii) indicates that PMax increases with increasing engine load, as the engine warms up.

In this example, up to a load of about 400 Nm, PMax will increase steadily.

Where the invention is not employed, it can be seen that where the injection timing is advanced to the second regime, the pressure PMax will surge, as indicated by the dotted line (i). The design pressure rating of the engine 10 may for example, be around 200 bar, and it can be seen that this pressure could be exceeded above loads of about 625 Nm.

This can occur where an existing engine 10 which is able to operate so that the maximum combustion chamber pressure PMax does not exceed the * 12 design maximum even when operated at high load in accordance with an advanced timing regime, is modified, or its operation is modified, e.g. to provide additional power in normal (non-advanced timing, regime) operation.

However by employing the invention, in the example when the PMax is in the order of 130 bar, the timing regime will revert to a normal, non-advanced, timing regime, in which use the PMax will, as engine load continues to increase, follow the full line (ii) and PMax will as a result, not rise above about bar in the example, i.e. PMax will remain well below the 200 bar design maximum pressure.

The problem of the maximum combustion chamber pressure PMax possibly exceeding the design maximum (of 200 bar in the example) is particularly but not exclusively highlighted where the engine 10 is to be used for example for driving an electrical generator 35. An engine 10 used to drive a generator 35 is generally operated at a constant speed condition, and is of the fixed governor kind. The engine 10 speed, upon start up, rapidly increases to the operating speed, say 1500 rpm, and high operating load may ensue. As explained above, if the operating torque of the engine 10 driving the generator 35 is above 400 Nm in this example, with the engine being operated according to an advanced timing regime, there is a real risk that the maximum combustion chamber pressure PMax could exceed the design maximum for the engine 10, and this could lead to damage to the conversion hardware of the engine 10.

In accordance with the invention, there is provided a second, pressure, sensor S2. This second sensor S2 in the example is provided to sense the pressure of the pressurised charge air between the compressor 20 and the charge cooler 25. Because the amount of pressurisation of the charge air is dependent upon the operation of the compressor 20, which in turn is dependent upon the * 13 operation of the turbine 16, which depends on the engine exhaust gas pressure and hence the pressure in the or each combustion chamber, it will be appreciated that the pressure sensed by the second, pressure, sensor S2 is indicative of, i.e. depends on (according to a complex relationship), the maximum pressure PMax attained in the or each of the combustion chambers.

The second, pressure, sensor S2 provides an input to the controller 31.

In the event that the engine 10 is being operated in accordance with an advanced timing regime as explained above, during a start-up period as the engine 10 warms up, if the signal from the second, pressure, sensor S2 indicates that the maximum combustion chamber pressure PMax may be rising above a desired pressure at which damage to the engine could occur, the controller 31 responds by operating the solenoid 30 or other actuator, to change the timing regime to the first, normal, timing regime, i.e. in which fuel injection timing is not advanced. In this way, the engine 10 is protected from excess combustion chamber pressures, as the maximum combustion chamber pressure PMax will then be limited as indicated by line (ii) in figure 3, to well below the maximum design combustion chamber pressure for the engine 10.

It can be seen in figure 3 that the controller 31 does not operate to change to a non-advanced timing regime only when the maximum combustion chamber pressure PMax is already surging, but when the maximum combustion chamber pressure PMax is lower than that, corresponding in the example to an engine 10 load (torque) of about 400 Nm. Above this engine 10 load, although misfires due to the engine 10 being cold can occur, these are less likely than at lighter loads and so it is acceptable to change to a non-advanced timing regime well in advance of a risk of a pressure surge. * 14

Thus, the threshold pressure sensed by the second pressure sensor S2 at which the controller 31 changes the timing regime back to the first, normal, non-advanced regime, is arranged to be a threshold pressure indicative of a PMax significantly below the maximum design pressure.

Various modifications are possible without departing from the scope of the invention.

In the embodiment described, the first, temperature, sensor SI senses the temperature of an engine 10 coolant but could sense another temperature indicative of the engine 10 temperature.

The actuator 30 for changing the timing component to and from an advanced timing regime need not be a solenoid 30, but any other preferably, but not essentially, electrically controlled actuator 30. The controller 31 is desirably incorporated into the engine 10 management system and the controller 31 may be responsive to other inputs in addition to the first, temperature, sensor Si, and then the second, pressure, sensor S2, for the purposes of controlling fuel metering to the engine 10 and otherwise controlling the engine 10 for maximum efficiency/lowest emissions.

The invention has specifically been devised to enable an existing engine 10 design to be modified, or its operation to be modified, and used for driving a generator 38 as part of a genset, but the invention has application for other engine 10 uses, especially but not exclusively where the engine 10 is required to run in constant high load conditions, e.g. static engines, or vehicle engines for series hybrid vehicles for examples. The invention may be employed for engines 10 which drive excavating and loading machines, or tractors or the like working machines and vehicles. * 15

The second, pressure, sensor S2 need not be located where suggested, but could otherwise be located. The second, pressure, sensor S2 could sense directly the (or a) combustion chamber pressure, but sensors able to survive such operating conditions tend to be overly expensive and unreliable. The second, pressure, sensor S2 could sense exhaust gas pressure, e.g. in exhaust manifold 15, or the second sensor S2 could even detect turbine speed as an indicator of combustion chamber pressure or another such parameter which is indicative of the pressure in the or each of the combustion chambers of the engine 10.

Where the second, pressure, sensor S2 senses indirectly the combustion chamber pressure, calibration will be required to set the pressure or other parameter sensed at which the controller 31 changes the timing regime to the first, normal, timing regime, corresponding to a desired pressure in the or a combustion chamber which is if desirable not to exceed, to ensure that the controller 31 changes from the second, advanced timing regime to the first, normal, timing regime before there is real risk of a pressure surge which could increase the maximum combustion chamber pressure PMax to above the design maximum for the engine 10.

Although the invention has been described in relation to a turbocharged compression ignition engine 10, e.g. a diesel engine, the invention may be applied to a non-turbocharged compression ignition engine 10, for example an engine 10 where the air charge is unpressurised, or to a supercharged engine 10. In each of these cases, the second, pressure, sensor S2 would require to be provided at an alternative location to that suggested in the example.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for * 16 attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof. * 17

Claims

CLAIMS1. A method of operating a compression ignition engine which includes at least one combustion chamber containing a piston, to which combustion chamber is delivered fuel by a mechanically operated fuel injection pump apparatus, the method including sensing the engine temperature or a temperature associated with the engine with a first sensor, and providing an input to a controller, the controller operating the fuel injection pump apparatus to deliver fuel to the or each of the combustion chambers according to a first timing regime when the sensed temperature is above a threshold temperature, and according to a second, advanced timing, regime when the sensed temperature is below the threshold temperature, the method further including sensing with a second sensor the pressure in the or at least one of the combustion chambers or a parameter which is indicative of the pressure in the or each of the combustion chambers, and when the controller is operating the fuel injection pump apparatus according to the second timing regime and the sensed pressure or other parameter exceeds a threshold which indicates a pressure in the or each of the combustion chambers above a desired pressure, the method including changing operation of the fuel injection pump apparatus from the second to the first timing regime.
2. A method according to claim 1 wherein the second sensor senses a pressure which is indicative of the maximum pressure being experienced in a or the or each of the combustion chambers.
3. A method according to claim 2 wherein the engine is turbocharged, with the exhaust gases acting on a turbine which drives a compressor to pressurise charge air which is introduced into the or each combustion chamber for combustion, the second sensor sensing one of the pressure of the exhaust gases, and the pressure of the pressurised air. * 18
4. A method according to claim 3 wherein the pressurised charge air is passed through a charge cooler to cool the pressurised charge air prior to the charge air being introduced into the or a combustion chamber, and the second sensor senses the pressure of the charge air between the compressor and the charge air cooler, which will vary depending upon the pressure in the combustion chamber or chambers.
5. A method according to any one of the preceding claims wherein the fuel injection pump apparatus includes an actuator which responds to a control signal from the controller, to move a timing component of the fuel injection pump apparatus to a position where the onset of fuel injection in each combustion cycle is advanced, until either the sensed temperature reaches the threshold temperature, or until the threshold pressure or other parameter is sensed by the second sensor when the actuator moves the timing component or permits the timing component to move back to a normal position so that the onset of fuel injection returns to a normal non-advanced, first, timing regime.
6. A method according to any one of the preceding claims wherein the method includes changing operation of the fuel injection pump apparatus from the second to the first timing regime when the sensed pressure or other parameter indicates that the pressure in the combustion chamber or chambers is significantly lower than the maximum design pressure of the engine.
7. A method according to any one of the preceding claims which includes using the engine to drive a generator, and operating the engine at a generally constant load.
8. A method according to claim 7 wherein the engine is of the fixed speed-governor kind. * 19
9. A method of operating a compression ignition engine substantially as hereinbefore described with reference to the accompanying drawings.
10. An apparatus including an electrical generator and an engine to drive the generator, the engine including at least one combustion chamber containing a piston, to which combustion chamber is delivered fuel by a mechanically operated fuel injection pump apparatus, there being a first sensor to sense the engine temperature or a temperature associated with the engine and to provide an input to a controller, the fuel injection pump apparatus being operable by the controller to deliver fuel to the or each of the combustion chambers according to a first timing regime when the sensed temperature is above a threshold temperature, and according to a second advanced timing regime when the sensed temperature is below the threshold temperature, and there being a second sensor to sense the pressure in the or at least one of the combustion chambers or a parameter which is indicative of the pressure in the or each of the combustion chambers, and the controller, when operating the fuel injection pump apparatus according to the second, advanced, timing regime, upon the second sensor sensing a threshold pressure or other parameter threshold which indicates a pressure in the or each of the combustion chambers above a desired pressure, changing operation of the fuel injection pump apparatus from the second to the first timing regime.
11. An apparatus substantially as hereinbefore described with reference to and/or as shown in the accompanying drawings.