GB1595060A - Air heater system - Google Patents

Description

(54) AIR HEATER SYSTEM (71) We, LUCAS INDUSTRIES LI MITED, a British Company of Great King Street, Birmingham B19 2XF England, do hereby declare the invention for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to an air heater system for a compression ignition engine of the kind which is described and claimed in our co-pending application 25823/76, Serial No. 1548937.

In order to facilitate the starting of a compression ignition engine it is necessary to supply heat to the engine and the most convenient way of doing this is to burn fuel in a combustion chamber which is disposed in, or forms part of an air inlet to the engine.

The supply of fuel to the combustion chamber must be carefully controlled in order that the correct amount of heat is supplied.

Moreover, in the case of a supercharged compression ignition engine it is often necessary to maintain the supply of heat during running of the engine in order to ensure that proper combustion of fuel injected into the combustion space or spaces of the engine, takes place. Whilst the engine is running the amount of heat supplied must also be carefully controlled.

The object of the present invention is to provide an air heater system for a compression ignition engine in a simple and convenient form.

According to the invention an air heater system for a super-charged compression ignition engine comprises a combustion chamber including a burner through which fuel is suppied to the combustion chamber, a two stage fuel pump for suppying fuel to the burner, the output of the second stage being connected to the burner and the input of the second stage being connected to the output of the first stage the input of which is, in use, connected to a source of fuel under pressure, the rate of fuel delivery of said pump being dependent upon the speed at which the pump is driven, first motor means for driving said pump, valve means operable in use to ensure that there is substantially no pressure drop across the second stage of the pump, control means for controlling the speed of operation of the first motor means and thereby the rate of fuel supplied to the burner, first means for providing an engine speed signal or signals to said control means and second means for providing a signal representative of the load on the engine to said control means, said control means being responsive to said signals and acting to cause fuel to be supplied to the burner when the engine speed is below a predetermined value and the load on the engine is below a predetermined value.

An example of an air heating system in accordance with the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a diagrammatic layout of the system as applied to a compression ignition engine and Figure 2 is a block diagram of a portion of the system of Figure 1.

Referring to Figure 1 of the drawings, there is shown a compression ignition engine 10 of Vee type and having air inlet manifolds 11, 12. The inlet ends of the air inlet manifolds communicate by way of a junction member 13, with the outlet of a combustion chamber 14 and the inlet end of the combustion chamber 14 communicates by way of a pipe 15 with the outlet of the compressor section of a turbo-supercharger (not shown). The turbine of the turbosupercharger is driven by exhaust gases produced when the engine is in operation.

Conveniently, the combustion chamber 4 is of a type similar to that which is described and claimed in our British Application 47951/74, Serial No. 1524677.

The combustion chamber 14 incorporates a burner assembly to which liquid fuel is supplied by way of an inlet 16 and air under pressure by way of an inlet 17. The air under pressure is provided by means of an air pump generally indicated at 18 and which draws air from the pipe 15 at a position upstream of the combustion chamber.

The combustion chamber 14 also accommodates an ignition device such for example as a spark plug and electrical energy is supplied to the ignition device by means of a unit 19.

The inlet 16 is connected to the outlet of a fuel pump generally indicated at 20 but incorporated between the outlet of the pump and the inlet is an electrically operated valve 21. The purpose of this valve is to ensure that when the fuel pump 20 is not in operation, the pressure of air within the combustion chamber 14 due to the operation of the supercharger, will not force fuel back through the pump. The inlet of the fuel pump is connected to a source of fuel under pressure and this, for example, is shown as a pump 22 conveniently accommodated in a fuel tank of the vehicle with which the engine is associated. The pump 22 is electrically driven and is powered from the vehicle accumulator or accumulators.

As will be seen from Figure 1, the pump 20 is a two-stage pump the first stage being indicated at 23 and the second stage at 24.

The two stages are positive displacement pumps which are driven by means of an electric motor (not shown). The displacement of the first stage is conveniently twice that of the second stage. Moreover, a valve generally indicated at 25 is provided to ensure that substantially no pressure drop occurs between the inlet and outlet of the second stage 24 of the pump 20. The output of the pump 20 is therefore proportional to the speed at which it is driven and the delivery of fuel to the combustion chamber can be readily controlled by altering the speed of the drive motor. The construction of the pump 20 and the valve 25 is described in greater detail in our co-pending application 25823/76. Serial No. 1548937.

The pump provides for widely varying flow rates of fuel to the combustion chamber and in one example, a variation of between 0.3-4.0 gallons of fuel per hour is required. This is readily achieved by varying the speed of the motor and it has been found that even when the motor is operating at a relatively low speed to provide the low flow rate of fuel to the burner, there is substantially no variation in the actual flow rate even though appreciable variation in the output pressure of the pump 22 occurs.

In the particular example, the engine 10 has twelve cylinders and fuel is supplied to the combustion spaces of the engine by way of fuel injection nozzles, one of which is indicated at 26, it being appreciated that there are twelve such nozzles. Fuel is supplied to the nozzles at the appropriate time, by means of a pumping apparatus 27 which includes a cam shaft on which are mounted twelve cams for actuating individual injection pumps associated with the nozzles 26 respectively. The cam shaft of the pumping apparatus 27 is driven through a coupling 28 from the engine 10.The quantity of fuel which is supplied to the engine by the apparatus is varied in known manner, by means of an adjustable control rod shown in dotted outline at 29a, the setting of which is determined in the particular example, by means of an electromagnetic actuator which is located within a housing 29 secured to the body of the apparatus 27. Also provided within the aforesaid housing is a transducer which can provide an electrical signal indicative of the actual position of the aforesaid control rod.

The supply of current to the electromagnetic actuator which determines the setting of the control rod 29a is under the control of a control circuit generally indicated at 30. The control circuit receives a demand signal from a transducer 31 associated with the throttle pedal 32 and in addition it receives various signals indicative of engine operating conditions. One such signal is provided by a transducer 33 providing an indication of the pressure of air which is being supplied to the engine. A further such signal is provided by a temperature sensor 34 which provides an indication of the temperature of a metallic part of the engine structure. Further sensors 35 are provided which indicate the temperature of the exhaust of the engine. Also located within the housing 29 is a transducer which provides a signal indicative of the speed of the apparatus and therefore the engine. The signals provided by the various components are processed in the control circuit 30 and a signal is provided to the electromagnetic actuator which sets the control rod 29a so as to provide a fuel level which, so far as possible, enables the engine to meet the demand placed upon it by the operator of the vehicle. If the demand is such that for example, overspeeding of the engine would occur, then the control circuit limits the amount of fuel supplied to maintain the engine speed at a safe value. The signals provided by the sensors 34 and 35 are also utilised to effect a control of the fuel supplied to the engine under certain circumstances.

The compression ratio of the engine 10 since it is a supercharger engine, is lower than would be the case if the engine were un-supercharged. It is therefore necessary when starting the engine, to heat the air which is supplied to the engine remembering that the supercharger will not be effective to provide air under pressure at the cranking speed or even whilst the engine is running under light load conditions. The combustion chamber 14 when it is supplied with fuel and air, heats the air flowing to the engine to promote rapid starting of the engine and also during light load running of the engine, to improve the combustion of the fuel which is supplied to the engine by the pumping apparatus 27.

Reference will now be made to Figure 2 of the drawings which shows in block form the various components associated with the combustion chamber 14 and including electronic components for controlling the generation of heat by the combustion chamber. It will be noted that downstream of the combustion chamber and in practice, in the inlets of the air inlet manifolds 11, 12 there is mounted a temperature sensor 36. This sensor senses the temperature of the air supplied to the manifolds which varies in accordance with the amount of fuel which is supplied to the combustion chamber. Also shown in Figure 2 is the drive motor 37 for the fuel pump 20 together with a transducer 38 which provides a signal indicative of the speed of rotation of the motor 37.

During the starting phase of the engine, it is required to supply fuel to the combustion chamber at a constant rate. In this manner the temperature of the air flowing through the inlet manifolds of the engine depends upon the cranking speed of the engine.

Once the engine has reached its idling speed, then the control of fuel to the combustion chamber when the engine is running on light load, is arranged in accordance with the temperature of air sensed by the sensor 36. During this phase therefore there is closed loop control of the temperature. It will be appreciated that the supply of fuel to the combustion chamber must be prevented if for some reason the engine should stop or be stopped and it is also required to prevent fuel supply to the combustion chamber in the event that the engine speed exceeds a predetermined value. Moreover, once the load of the engine has attained a predetermined value, the combustion of fuel by the engine will proceed in a satisfactory manner without the need to pre-heat the air supplied to the engine.The control system for the various components includes a logic unit 39 which receives a first input at terminal 40 indicative of the load on the engine. The logic unit also receives at an input 41, a signal indicative of the fact that the engine speed is below a predetermined value and a further signal at an input 42 indicative of the actual engine speed. The speed of the motor 37 is determined by a control 43 which receives an input signal from the temperature sensor 36 and also at an input 44, a reference signal appropriate to the temperature of air required to be supplied to the engine when the engine has started. As has been said however, during the starting of the engine fuel is supplied to the combustion chamber at a constant rate and the supply of fuel and also air is initiated when during cranking, the engine speed exceeds a predetermined low value for example 60 r.p.m.When the engine speed attains this value the air pump 18 the igniter supply 19 and the motor 37 are energised and a flame is established in the combustion chamber. If for some reason, a flame is not established within a predetermined time, the flame being detected by means of the sensor 36, then the system is turned off and cannot be restarted until the engine speed is allowed to fall below the aforementioned predetermined low value.

When the engine starts and its speed attains a second value in the particular example, 400 r.p.m, the unit 19 is de-energised and the logic unit switches the control 43 so that the aforementioned closed loop control of the fuel is obtained. The reference applied at the terminal 44 sets the value of the air temperature of air flowing in the air inlet manifolds and the control adjusts the speed of the motor 37 so as to achieve this temperature. The supply of fuel continues and is controlled either until the engine speed exceeds a predetermined value or the load on the engine attains a predetermined value. When either of these values is attained, the system is shut off and the engine allowed to operate without the supply of fuel to the combustion chamber.If after, a period of use under load, the load is reduced, then when both the engine speed and the load fall below the aforesaid values, the supply of fuel to the combustion chamber will be re-established. Conveniently the unit 19 supplies energy to the sparking plug whenever the temperature of the air flowing in the manifold is below a predetermined value. In this manner ignition of the fuel supplied to the combustion chamber will be quickly established. The supply of energy by the unit 19 is however prevented when the temperature sensed by the sensor 36 indicates that a flame is established and when the engine is operating within a predetermined engine speed band above idling speed.

The signal representative of the load on the engine was obtained as described in the parent specification, from the pressure sensor 33 disposed downstream of the turbo supercharger. It has been found that the signal provided by this sensor whilst being sufficiently stable and accurate for use in determining the fuel supply to the engine is not suitable for providing the signal representative of the load on the engine for application to the terminal 40 of the logic unit. It is proposed therefore to apply a signal to the terminal 40 from another device which provides a signal representative of the load on the engine.

One such device is the exhaust gas temperature sensor 35 or a specially provided temperature sensor. The temperature of the exhaust gas is representative of the load on the engine since the temperature of the exhaust gas increases as the fuel supplied to the engine increases. Another device which may be used to provide the load signal is the transducer in the casing 29 and which as described supplies a signal indicative of the setting of the control member 29a for the purpose of controlling the fuel supply to the engine. This transducer or a similar transducer may be provided.

A further device which may be used to provide the signal is a speed transducer which senses the speed of operation of the turbo supercharger. The turbo supercharger speed is again influenced by the load on the engine since it depends upon the mass flow of exhaust gas and the temperature of the exhaust gas.

It will be appreciated that the combustion chamber 14 has similar properties to the combustion chamber of a gas turbine engine, and therefore the regulation of the supply of fuel to the combustion chamber must be carefully controlled to avoid the flame being extinguished either because too much fuel is being supplied, or because too little fuel is being supplied. It is clear, however, that with increasing engine speed more fuel must be supplied to the combustion chamber in order to maintain the desired temperature of air supplied to the engine. It will be understood that whenever it is required that fuel should be supplied to the combustion chamber the valve 21 shown in Figure 1 must be opened.The valve however is closed as soon as fuel is no longer required to prevent air forcing the fuel back through the fuel pump and thereby prevent ing rapid establishment of the flame in the combustion chamber when it is next required.

WHAT WE CLAIM IS: 1. An air heater system for a supercharged compression ignition engine comprising a combustion chamber including a burner through which fuel is supplied to the combustion chamber, a two stage fuel pump for supplying fuel to the burner, the output of the second stage being connected to the burner and the input of the second stage being connected to the output of the first stage the input of which is, in use, connected to a source of fuel under pressure, the rate of fuel delivery of said pump being dependent upon the speed at which the pump is driven, first motor means for driving said pump, valve means operable in use to ensure that there is substantially no pressure drop across the second stage of the pump, control means for controlling the speed of operation of the first motor means and thereby the rate of fuel supplied to the burner, first means for providing an engine speed signal or signals to said control means and second means for providing a signal representative of the load on the engine to said control means, said control means being responsive to said signals and acting to cause fuel to be supplied to the burner when the engine speed is below a predetermined value and the load on the engine is below a predetermined value.

2. An air heater system according to claim 1 in which said second means comprises a temperature sensor disposed in the exhaust system of the engine.

3. An air heater system according to claim 1 in which said second means comprises a transducer associated with the fuel quantity control of the fuel pump which supplies fuel to the engine.

4. An air heater system according to claim 1 in which said second means comprises a transducer associated with the supercharger of the engine and which supplied a signal indicative of the speed thereof.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. determining the fuel supply to the engine is not suitable for providing the signal representative of the load on the engine for application to the terminal 40 of the logic unit. It is proposed therefore to apply a signal to the terminal 40 from another device which provides a signal representative of the load on the engine. One such device is the exhaust gas temperature sensor 35 or a specially provided temperature sensor. The temperature of the exhaust gas is representative of the load on the engine since the temperature of the exhaust gas increases as the fuel supplied to the engine increases. Another device which may be used to provide the load signal is the transducer in the casing 29 and which as described supplies a signal indicative of the setting of the control member 29a for the purpose of controlling the fuel supply to the engine. This transducer or a similar transducer may be provided. A further device which may be used to provide the signal is a speed transducer which senses the speed of operation of the turbo supercharger. The turbo supercharger speed is again influenced by the load on the engine since it depends upon the mass flow of exhaust gas and the temperature of the exhaust gas. It will be appreciated that the combustion chamber 14 has similar properties to the combustion chamber of a gas turbine engine, and therefore the regulation of the supply of fuel to the combustion chamber must be carefully controlled to avoid the flame being extinguished either because too much fuel is being supplied, or because too little fuel is being supplied. It is clear, however, that with increasing engine speed more fuel must be supplied to the combustion chamber in order to maintain the desired temperature of air supplied to the engine. It will be understood that whenever it is required that fuel should be supplied to the combustion chamber the valve 21 shown in Figure 1 must be opened.The valve however is closed as soon as fuel is no longer required to prevent air forcing the fuel back through the fuel pump and thereby prevent ing rapid establishment of the flame in the combustion chamber when it is next required. WHAT WE CLAIM IS:

1. An air heater system for a supercharged compression ignition engine comprising a combustion chamber including a burner through which fuel is supplied to the combustion chamber, a two stage fuel pump for supplying fuel to the burner, the output of the second stage being connected to the burner and the input of the second stage being connected to the output of the first stage the input of which is, in use, connected to a source of fuel under pressure, the rate of fuel delivery of said pump being dependent upon the speed at which the pump is driven, first motor means for driving said pump, valve means operable in use to ensure that there is substantially no pressure drop across the second stage of the pump, control means for controlling the speed of operation of the first motor means and thereby the rate of fuel supplied to the burner, first means for providing an engine speed signal or signals to said control means and second means for providing a signal representative of the load on the engine to said control means, said control means being responsive to said signals and acting to cause fuel to be supplied to the burner when the engine speed is below a predetermined value and the load on the engine is below a predetermined value.

2. An air heater system according to claim 1 in which said second means comprises a temperature sensor disposed in the exhaust system of the engine.

3. An air heater system according to claim 1 in which said second means comprises a transducer associated with the fuel quantity control of the fuel pump which supplies fuel to the engine.

4. An air heater system according to claim 1 in which said second means comprises a transducer associated with the supercharger of the engine and which supplied a signal indicative of the speed thereof.