GB2393999A

GB2393999A - Reduction of turbo-lag in an i.c engine

Info

Publication number: GB2393999A
Application number: GB0222988A
Authority: GB
Inventors: Martin Nicholas Green; Garon Nigel Heslop
Original assignee: Visteon Global Technologies Inc
Current assignee: Visteon Global Technologies Inc
Priority date: 2002-10-04
Filing date: 2002-10-04
Publication date: 2004-04-14
Anticipated expiration: 2022-10-04
Also published as: GB2393999B; GB0222988D0

Abstract

When the turbo-boost is insufficient at relatively low engine speeds, an air pump 64 is actuated to pump air 66 through an air bypass system 63, which bypasses the combustion chambers 4 of the engine, from the air inlet system 6 to the exhaust system 7 upstream of the tubocharger impeller 51 while the fuel supply system 10 delivers fuel 69 into the bypass air 66 separately of the delivery of fuel 14 to the combustion chambers. The mixture of bypass air 66 and fuel 69 then ignites downstream of the air pump 64 and upstream of the impeller 51 to create a boost to the exhaust gas 52 and thereby boost the impeller speed and reduce turbo lag. The system requires a lower electrical current than an electrically assisted turbo-boost system.

Description

1- 2393999

Reduction of Turbo-lag in an Internal Combustion Engine The present invention relates to the reduction of turbo-lag in an internal combustion engine.

Exhaust-gas driven turbochargers are often used as part of an internal combustion engine in order to boost the air intake and hence the power output of the engine. The turbocharger includes a turbine impeller situated in the exhaust gas flow 10 and which is connected to a compressor unit in the air inlet path. The turbocharger usually includes an exhaust gas bypass so that the amount of turbo boost can be controlled by controlling the amount of exhaust gas entering the turbine impeller as opposed to the amount of gas bypassing the 15 impeller. As the engine speed increases, there is an increasing amount of exhaust gas available to boost engine power and torque. However, at low engine speeds, the amount of turbocharger boost may be negligible.

20 This is particularly a problem when a driver wishes to overtake at low engine speeds. The turbine boost only becomes available once the engine speed has risen sufficiently - an effect referred to as "turbo-lag".

25 There are a number of approaches to reducing turbo-lag. A variable nozzle turbine can be controlled electronically to change the effective cross-section presented to the exhaust gasses. In this case, a wastegate bypass around the turbocharger impeller is not required. This does not 30 completely solve the problem of turbo-lag, but does improve transient response once the turbocharger becomes effective.

- 2 It is known to use an electric motor driven supercharger in series with the turbocharger compressor, or to include in the turbocharger itself an auxiliary electric motor. The electric motor is then energised to boost the inlet pressure during 5 the interval of turbo-lag. Such solutions can effectively eliminate turbo-lag, but at the cost of increased mechanical and electrical complexity and cost of the engine.

In motor vehicle racing applications using gasoline spark-

10 ignition engines, it is known to allow uncombusted air/fuel into the exhaust manifold, where the combustion of the fuel provides additional exhaust gas pressure to spin up the turbine at low engine speeds. This is done by retarding the ignition spark to between 35 to 40 after the top dead 15 centre position of the engine. This results in incomplete combustion in the cylinders. Unburned air/fuel mixture therefore enters the exhaust manifold where it combusts and provides additional gas to spin up the turbine impeller.

20 There are a number of serious problems with this approach, which is in any event not applicable to compression-ignition engines. First, the incomplete combustion in the cylinders lowers engine power, with the risk that the engine will stall before the turbo boost is available. Secondly, the limited 25 space in a typical engine compartment means that the turbine impeller needs to be close to the exhaust manifold. The result is that the turbine impeller is likely to be excessively heated by the exhaust manifold combustion, which may even extend into the impeller itself. Thirdly, compared 30 with a conventional engine, the exhaust manifold and exhaust system will need to be formed from stronger materials and incorporate more thermal insulation. Fourthly, the necessary

catalytic converter is likely to be damaged, or at least have its operating life shortened from the resultant higher temperatures in the exhaust system, and from the relatively uncontrolled and incomplete combustion in the exhaust 5 manifold. As a result, such engines have never been used for a mass production automobile, and are only seen in vehicles on the race track.

It is an object of the present invention to provide a more 10 convenient and versatile system and method for reducing turbo-lag in a turbocharged internal combustion engine.

According to the invention, there is provided an internal combustion engine, comprising: 15 - one or more combustion chambers; - a first air inlet system for aspirating the combustion chamber(s) with inlet air; - a fuel supply system including a combustion fuel system for delivering fuel to the combustion chamber(s); 20 - an exhaust gas system for venting exhaust gas from the combustion chamber(s); - a turbocharger for boosting the air charge to the combustion chamber(s), said turbocharger including in the exhaust gas system an exhaust-driven impeller and in the air 25 inlet system an impeller-driven compressor for compressing inlet air; - a second air inlet system for providing bypass air upstream of the impeller and which bypasses the combustion chamber(s); - an air pump arranged to pump bypass air from the second air 30 inlet system towards the exhaust gas system; wherein the fuel supply system includes a bypass fuel system

- 4 for delivering fuel into the bypass air and the engine further comprises a source of ignition downstream of the air pump which during engine operation serves to ignite the bypass air/fuel mixture downstream of the air pump and 5 upstream of the impeller to create a boost to the exhaust gas and hence a boost to the impeller speed.

Also according to the invention, there is provided a method of reducing turbo-lag in an internal combustion engine, the 10 engine comprising one or more combustion chambers, a first air inlet system) a fuel supply system; an exhaust gas system; a turbocharger including in the exhaust gas system an exhaust-driven impeller and in the air inlet system an impeller-driven compressor; a second air inlet system for 15 providing bypass air upstream of the impeller and which bypasses the combustion chamber(s); and an air pump; wherein the method comprises the steps of: i) aspirating the combustion chamber(s) with inlet air from 20 the first air inlet system; ii) delivering combustion fuel to the combustion chamber(s) using the fuel supply system; 25 iii) venting exhaust gas from the combustion chamber(s) via the exhaust gas system; iv) using said exhaust gas to drive the impeller and hence the compressor to boost the air charge to the combustion 30 chamber(s); v) using the air pump to pump bypass air through the second

- 5 air inlet system towards the exhaust gas system upstream of the impeller; vi) using the fuel supply system to deliver fuel into the 5 bypass air separately of the delivery of fuel to the combustion chamber(s) ) and vii) igniting the bypass air: fuel mixture downstream of the air pump and upstream of the impeller to create a boost to 10 the exhaust gas and thereby boost the impeller speed and reduce turbo lag.

The second air inlet system may draw air independently of the first air inlet system, for example, having a dedicated and 15 separate air entrance and air filter. Such an arrangement has the advantage that the air drawn by the second air inlet system is not robbed from the total amount of air drawn by the first air inlet system.

20 In a preferred embodiment of the invention, however, the second air inlet system is an air bypass between the first air inlet system and the exhaust gas system, and the air pump is arranged to pump bypass air from the first air inlet system through the air bypass towards the exhaust gas system.

25 Such an arrangement has the advantage of using common components in the air inlet systems, such as a common air filter. In addition, when the air pump and compressor are in series, then the air pressure downstream of the air pump is a product of the compression of the air by the compressor and 30 the air pump, which is helpful in achieving a pressure greater than the base pressure inside the exhaust system owing to exhaust gasses vented from the combustion chambers.

- 6 - In either case, neither the bypass air nor the bypass fuel pass through the combustion chambers, and so the combustion process in the combustion chambers is substantially 5 unaffected when the exhaust is boosted from the combustion of the bypass air and the bypass fuel. Furthermore, the bypass air/fuel ratio can be controlled in order to ensure a controlled and substantially complete bypass combustion. The source of ignition can also be sited or arranged to prevent 10 excessive heating of the downstream exhaust system particularly any catalytic converter.

In a preferred embodiment of the invention, the engine further comprises an engine control unit arranged to control 15 both the operation of the air pump and the fuel supply system so as to control independently the delivery of fuel to the combustion chamber(s) and the bypass air. The engine control unit may then also monitor various engine and vehicle operating parameters, such as engine temperature, engine 20 speed, wheel speed, transmission gear ratio, and driver demand in order to determine when the available engine output, particularly available torque, is insufficient to meet the driver demand. If the gap between driver demand and available torque is due to turbo lag, then the engine control 25 unit can be used to control the provision of bypass air and bypass fuel to boost the flow of gasses towards the impeller.

The electronic control unit may control the bypass air/fuel ratio with an open loop control system, for example using 30 look-up tables to determine the desired amounts of bypass air and bypass fuel in order to spin up the impeller. Preferably, however, the engine system further comprises an exhaust gas

- 7 - sensor for sensing the composition of the exhaust gas. The engine control unit is then responsive to said sensed exhaust gas composition to control an air: fuel ratio for the bypass air and the bypass fuel.

The bypass fuel system may include at least one fuel injector for injecting fuel into the pumped bypass air.

Usually, it will be the case that the exhaust gas system 10 includes one or more exhaust ports to the combustion chamber(s). In this case, the air bypass may reach the exhaust gas system upstream of the or each exhaust port. This helps to distance the combusted products of the bypass air/fuel from components downstream of the exhaust ports, 15 such as impeller blades or a catalytic converter. Since bypass combustion products will tend to cool as these move downstream in the exhaust system, this separation will help to protect any such components from excessive heating.

20 The air pump could be mechanically driven, for example from a crankshaft pulley, but preferably the air pump is driven by an electric motor. The power consumption of such a motor is significantly less than the electric power consumption of an electrically-driven supercharger in the air intake system, or 25 of an electrically assisted turbocharger.

In the simplest embodiment, the ignition source is an exhaust manifold which in use is heated by exhaust gas from the combustion chamber(s) above the flash point of the bypass 30 fuel and air.

However, it is preferred if the second air supply system

includes a mixing chamber into which the bypass fuel and bypass air are delivered. The mixing chamber then has a combustion gas outlet into the exhaust system. The mixing chamber is preferably formed from a heatresistant material 5 such as a ceramic material.

The mixing chamber may also include a catalyst to facilitate combustion of the bypass fuel with the bypass air, particularly if the engine or exhaust system is not fully 10 warmed up.

Similarly the mixing chamber may include a matrix, for example a metal mesh or a block of sintered metal, into which the bypass fuel and bypass air are channelled. The matrix is 15 then heated by the combustion of the bypass fuel in the bypass air. Such stored heat can be an effective ignition and may also facilitate more complete combustion of the bypass fuel and air.

20 If the fuel supply system includes a fuel rail for pressurized fuel supply to one or more fuel injectors to the combustion chamber(s), then the fuel rail may also provide pressurised fuel for the bypass fuel system.

25 The first air supply system may include an intercooler downstream of the compressor for cooling and raising the density of compressed inlet air, the air bypass being downstream of the intercooler. This helps the air pump to supply air above the pressure of the exhaust gasses in the 30 exhaust system.

The invention will now be further described, by way of

example only, and with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of an internal 5 combustion engine according to the invention, having a number of combustion chambers, and an air: fuel bypass which bypasses the combustion chambers to provide additional combustion gas into an exhaust manifold to reduce turbo-lag; Figure 2 is a plot showing how turbo-lag is reduced and vehicle acceleration improved in the engine of Figure It Figure 3A is a plot showing how an intake air flow rate 15 to the combustion chambers is changed when the air: fuel bypass is being used to reduce turbo-lag; Figure 3B is a plot showing how an intake air flow rate to the air: fuel bypass is changed when the air:fuel 20 bypass is being used to reduce turbo-lag) Figure 4 shows the increase in engine brake torque due to the reduction in turbo-lag; 25 Figure 5A shows the fuel flow rate for the engine combustion chambers; Figure 5B shows the fuel flow rate for the air: fuel bypass; and Figure 6 shows a flowchart depicting the method according to the invention of using an internal

- 10 combustion engine having a number of combustion chambers, and an air:fuel bypass which bypasses the combustion chambers to provide additional combustion gas into an exhaust manifold to reduce turbo-lag.

Figure 1 shows a schematic representation of an internal combustion engine 1 based around an engine block 2 that has four in-line cylinders 4 which, together with four reciprocating pistons (not shown), define four combustion 10 chambers for powering the engine. The engine 1 in this example is suitable for powering a motor vehicle (not shown).

An air inlet system 6 draws inlet air 8 for the cylinders 4.

The engine 1 also has a fuel supply system 10 including a 15 fuel rail 12 and four injectors 14, one for each of the cylinders 6.

The engine 1 in this example is a spark ignition gasoline engine, and so has four spark plugs 16, one for each of the 20 cylinders 6. The engine also has an electronically operated throttle 17 downstream of an air filter (F) 19 in the air inlet system 6. The invention is, however, also applicable to compression ignition engines, particularly diesel engines.

25 The engine 1 is run under the control of an electronic engine control system or unit (ECU) 18. The ECU may be a single unit, or distributed amongst several units. The ECU 18 sends fuel control signals (EFI) 20 to activate the fuel injectors 14, spark control signals (EI) 21 to activate the spark plugs 30 16, and a throttle control signal (ET) 22 to open and close the throttle 17.

The ECU 18 receives a number of control inputs, including an engine temperature signal ( C) 30 from an engine block temperature sensor 40, an engine speed signal (S) 31 from a crank shaft rotation sensor 41, a throttle position signal 32 5 from the electronic throttle 17, and a driver demand signal (DD) 33 from an electronic sensor 42 on a driveractuatable accelerator pedal 15.

The engine 1 has an exhaust gas system 7 and a turbocharger 10 (TC) 50, which spans both the air inlet system 6 and the exhaust gas system 7. A turbocharger impeller 51 in the exhaust gas system 7 is driven by engine exhaust gasses 52 vented from the cylinders 4 via an exhaust gas manifold 5 connected to the engine block 2. Optionally, one or more 15 sensors 43 for measuring pressure or temperature may be positioned in the exhaust gasses 52 and provide corresponding signals (ES) 34 to the ECU 18. The turbocharger 50 may also have a rotor speed sensor 45 and provide to the ECU an impeller/compressor speed signal (TS) 37.

The air inlet system 6 includes a turbocharger compressor 55 connected via a rotating shaft 54 to the impeller 51. The compressor is downstream of the air filter 19 and throttle 17 and receives filtered inlet air 9. When the compressor 55 is 25 turned by the impeller 51, the filtered inlet air 9 is compressed by the turbocharger 50. Air 11 downstream of the compressor 55 is supplied to an intercooler (IC) 56 which cools and increases the density of the compressed air 11. The cooled compressed air 13 is then supplied to the cylinders 4 30 via an inlet manifold 3 connected to the engine block 2. The compression of the inlet air allows a greater air charge to each cylinder and hence a greater amount of fuel to be

- 12 injected 14 into the cylinders, hence boosting engine power and output brake torque.

The turbocharger 50 is controlled under the action of the ECU 5 18, via a turbo bypass valve 57 that receives a turbo bypass signal 23. When the turbocharger 50 is not in use, the bypass valve 57 is set to direct exhaust gasses through a bypass 58 which bypasses the impeller 51. When the ECU 18 calculates that the engine 1 cannot meet the driver demand 33 using 10 natural aspiration alone, then the ECU commands 23 the bypass valve 57 to admit more exhaust gas to the impeller 51 and less through the bypass 58. The bypass valve 57 may also provide a bypass position signal 35 to the ECU 18.

15 Exhaust gasses 59 downstream of the turbocharger 50 are provided to a catalytic converter (CC) 60. The catalysed exhaust gasses 61 downstream of the catalytic converter 60 are monitored by an exhaust gas sensor 44, for example a heated exhaust gas sensor or a universal exhaust gas sensor, 20 which provides an exhaust gas composition signal (E) 38 to the ECU 18. The ECU then controls the air: fuel mixture to the cylinders 4 to maximise engine efficiency and minimise harmful exhaust gasses 61. Optionally, there may be another exhaust gas sensor (not shown) upstream of the catalytic 25 converter 60 and downstream of the impeller 51.

It is often the case that when the ECU 18 first requires turbocharger boost, the engine speed may be relatively low, with a consequently low volume of exhaust gas 52 produced by 30 the cylinders 4. The turbocharger impeller 51 will then take some time, for example a few seconds to approach full operating speed, e.g. 50,000 to 100,000 rpm, and hence full

- 13 turbo boost.

The engine 1 reduces this turbo-lag with a supplementary combustion system 100 which bypasses the cylinders 4 and 5 which introduces additional or supplementary combustion gas 62 into the exhaust manifold 5 until the exhaust gases produced by the cylinders 4 are sufficient to drive the impeller 51 at a desired speed.

10 The supplementary combustion system 100 includes a bypass air pump (BPA) 64 which is powered by an electric motor 53 that is energised in response to a control signal (BP) 24 from the ECU 18. Optionally, the bypass air pump 64 also sends a bypass pump speed signal 36 to the ECU 18 so that the ECU may 15 monitor the bypass pump speed.

When energised, the bypass air pump takes filtered cooled inlet air 65 and through an air bypass 63 supplies this bypass air 66 under pressure to an air:fuel mixing chamber 20 (M) 67 that is directly adjacent but upstream of the exhaust manifold 5. A bypass fuel injector 68 injects bypass fuel 69 into the mixing chamber 67, which is made from a heat resistant material such as a ceramic material. The mixing chamber 67 may optionally include a source of ignition, for 25 example a hot wire (not shown) to initiate ignition.

Otherwise, the source of ignition may be heat conducted from the body of the exhaust manifold 5 into the body of the mixing chamber 67.

30 The combustion of the bypass air 66 and bypass fuel 69 provides the supplementary combustion gas 62 to the exhaust manifold 5 in order to promptly spin up the turbocharger

- 14 impeller 51.

The air: fuel mixture in the mixing chamber 67 is controlled by the ECU to ensure substantially complete combustion of the 5 mixture prior to the supplementary combustion gas 62 entering the exhaust manifold 5. This helps to prevent excessive heating of the turbocharger impeller 51, and to prevent excessive unburned fuel from reaching the catalytic converter 60. Figures 2, 3A, 3B, 4, 5A and 5B show the effect of the supplementary combustion system 100 in reducing turbo lag for a passenger car having a 2 litre four-cylinder gasoline engine. Figure 2 shows a plot of the vehicle speed against 15 time, both with and without the operation of the supplementary combustion system 100. Until 2 seconds, the vehicle speed is constant at about 32 km/in. A maximum driver demand is then applied and the vehicle speed begins to rise steadily. A solid lower line 70 plots the change in speed 20 without the use of the supplementary combustion system 100.

An uppermost intermittently dashed line 72 plots the change in vehicle speed for a bypass fuel supply rate of 0.9 kg/hour. An intermediate dashed line 71 plots the change in vehicle speed for a bypass fuel supply rate of 25 0.45 kg/hour. In the 4 to 5 second interval following the increase in the driver demand, the acceleration of the vehicle with the use of the supplementary combustion system 100 is greater than without, as can be seen from the greater slope of the dashed and intermittently dashed lines 71,72 as 30 compared with the solid line 70.

Figures 3A and 3B show the change in the volume of the total

- 15 inlet air respectively upstream and downstream of the bypass air pump 64 and the inlet manifold 3. A solid line 73 plots the change in the volume of upstream air 8,9,11 without the use of the supplementary combustion system 100. An uppermost 5 intermittently dashed line 75 plots the change in air volume for a bypass fuel supply rate of 0.9 kg/hour. An intermediate dashed line 74 plots the change inlet air for a bypass fuel supply rate of 0.45 kg/hour. The volume of inlet air is significantly boosted for about 6 seconds following the 10 increase in driver demand. Referring to Figure 3B, the airflow 66 downstream of the air pump 64 is initially zero, as shown by the solid line 76, and is thereafter constant at either a lower level 77 for the lower bypass fuel rate or an upper level 78 for the higher bypass fuel rate.

Figure 4 shows a plot of the engine brake torque against time, both with and without the operation of the supplementary combustion system 100. Until 2 seconds, the brake torque is constant at about 12 Nm. A maximum driver 20 demand is then applied and the engine torque suddenly rises.

A solid lower line 80 plots the change in torque without the use of the supplementary combustion system 100. An uppermost intermittently dashed line 82 plots the change in engine torque for the bypass fuel supply rate of 0.9 kg/hour. An 25 intermediate dashed line 81 plots the change in engine torque for the bypass fuel supply rate of 0.45 kg/hour. In the 4 to 5 second interval following the increase in the driver demand, the engine torque with the use of the supplementary combustion system 100 is greater than without, as can be seen 30 from the separation of the dashed and intermittently dashed lines 81,82 as compared with the solid line 80.

- 16 Figures 5A and 5B show the change in the fuelling rate respectively for the engine cylinders 4 and the supplementary combustion system 100. A solid line 83 plots the change in the cylinder fuelling rate without the use of the 5 supplementary combustion system 100. An uppermost intermittently dashed line 85 plots the change in the cylinder fuelling rate when the bypass fuel supply rate is 0.9 kg/hour. An intermediate dashed line 84 plots the change cylinder fuelling rate when the bypass fuel supply rate is 10 0.45 kg/hour. The cylinder fuelling rate is boosted in less than one second, and remains substantially boosted for 5 to 6 seconds after the initial increase in driver demand.

Referring to Figure 5B, the fuelling rate to the supplementary combustion system 100 is initially zero, as 15 shown by the solid line 86, and is thereafter constant at either a lower level 87 for the lower bypass fuel rate or an upper level 88 for the higher bypass fuel rate.

Figure 6 shows a flowchart 90 that explains the steps taken 20 by the ECU 18 to monitor and control the operation of the engine 1, depending on whether or not the use of the supplementary combustion system 100 is required.

The ECU 18 sets 91 the position of the electronic throttle 25 17, and also schedules 92 the fuel delivery and the spark angle to the combustion chambers 4, according to the current level of driver demand 33. The ECU 18 also concurrently monitors 93 various engine operating parameters, including engine speed 31 and the turbine speed 37. The ECU monitors 94 30 both the current driver demand 33 and the rate of change of driver demand, and tests 95 whether or not the engine can meet the present and expected levels of driver demand. If so,

- 17 then the ECU continues to set 91 the throttle position and schedule 92 the fuel delivery and spark angle.

If, however, the driver demand cannot be met, then the ECU 18 5 tests 96 if the exhaust gas boost can help the engine to meet the current and expected driver demand. This may not be the case, if the turbocharger 50 is already spinning at its operational speed, in which case, the flow chart loops back as explained above to the steps 91 and 92.

When the exhaust gas boost can help the engine to meet the present and expected driver demand, then the ECU 18 schedules 97 the operation of the bypass air pump 64 and also the bypass fuel delivery 69 in order to reduce turbo lag.

15 Thereafter, the flow chart loops back as explained above to the steps 91 and 92.

The system described above offers significant advantages to prior art turbo-lag reduction systems. In particular, the

20 supplementary combustion system 100 is relatively simple both mechanically and electrically. The bypass air pump requires only a modest amount of electrical current from a vehicle power supply system, of the order to 100 W to 200 W. or 7 A to 15 A from a 13.6 V battery/alternator system. The 25 supplementary combustion system 100 therefore draws far less current that an electrically assisted turbo boost or supercharger system, which may need to consume as much as 200 A to 300 A. 30 In addition, compared with electrically assisted systems, the supplementary combustion system 100 is inherently efficient, because this avoids the inevitable losses in the bi

- 18 directional conversion and storage of mechanical energy to/from electrical energy.

The engine 1 described above also avoids problems associated 5 with exhaust manifold combustion of unburned fuel passed through the cylinders 4, in particular excessive heating of the exhaust system and turbocharger, and incompatibility with catalytic converters. The invention is also applicable to either spark ignition or to compression ignition engines.

The invention therefore provides a useful and convenient solution to the problem of turbo-lag in an internal combustion engine.

Claims

- 19 Claims

1. An internal combustion engine, comprising: - one or more combustion chambers) 5 - a first air inlet system for aspirating the combustion chamber(s) with inlet airs - a fuel supply system including a combustion fuel system for delivering fuel to the combustion chamber(s)) - an exhaust gas system for venting exhaust gas from the 10 combustion chamber(s); - a turbocharger for boosting the air charge to the combustion chamber(s), said turbocharger including in the exhaust gas system an exhaust-driven impeller and in the air inlet system an impeller- driven compressor for compressing 15 inlet airs - a second air inlet system for providing bypass air upstream of the impeller and which bypasses the combustion chamber(s); - an air pump arranged to pump bypass air from the second air inlet system towards the exhaust gas system) wherein the fuel supply system includes a bypass fuel system for delivering fuel into the bypass air and the engine further comprises a source of ignition downstream of the air pump which during engine operation serves to ignite the 25 bypass air/fuel mixture downstream of the air pump and upstream of the impeller to create a boost to the exhaust gas and hence a boost to the impeller speed.

2. An internal combustion engine as claimed in Claim 1, in 30 which the second air inlet system draws air independently of the first air inlet system.

- 20

3. An internal combustion engine as claimed in Claim 1, in which the second air inlet system is an air bypass between the first air inlet system and the exhaust gas system, and the an air pump is arranged to pump bypass air from the first 5 air inlet system through the air bypass towards the exhaust gas system.

4. An internal combustion engine as claimed in Claim 3, further comprising an engine control unit arranged to control 10 both the operation of the air pump and the fuel supply system so as to control independently the delivery of fuel to the combustion chamber(s) and the bypass air.

5. An internal combustion engine as claimed in Claim 4, 15 further comprising an exhaust gas sensor for sensing the composition of the exhaust gas the engine control unit being responsive to said sensed exhaust gas composition to control an air: fuel ratio for the bypass air and the bypass fuel.

20

6. An internal combustion engine as claimed in any of Claims 3 to 5, in which the first air supply system includes an intercooler downstream of the compressor for cooling and raising the density of compressed inlet air, the air bypass being downstream of the intercooler.

7. An internal combustion as claimed in any preceding claim, in which the bypass fuel system includes at least one fuel injector for injecting fuel into the pumped bypass air.

30

8. An internal combustion engine as claimed in any preceding claim, in which the exhaust gas system includes one or more exhaust ports to the combustion chamber(s) and the

- 21 bypass air reaches the exhaust gas system upstream of the or each exhaust port.

9. An internal combustion engine as claimed in any 5 preceding claim, in which the air pump is driven by an electric motor.

10. An internal combustion engine as claimed in any preceding claim, in which the second air supply system 10 includes a mixing chamber into which the bypass fuel and bypass air are delivered and combusted, the mixing chamber having a combustion gas outlet into the exhaust system.

11. An internal combustion engine as claimed in Claim 10, in 15 which the mixing chamber is formed from a ceramic material.

12. An internal combustion engine as claimed in Claim 10 or Claim 11, in which the mixing chamber includes a catalyst to facilitate combustion of the bypass fuel with the bypass air.

13. An internal combustion engine as claimed in any of Claims 10 to 12, in which the mixing chamber includes a matrix into which the bypass fuel and bypass air are channelled, the matrix being heated by the combustion of the 25 bypass fuel in the bypass air.

14. An internal combustion engine as claimed in any preceding claim, in which the ignition source is an exhaust manifold which in use is heated by exhaust from the 30 combustion chamber(s) above the flash point of the bypass fuel and air.

- 22

15. An internal combustion engine as claimed in any preceding claim, in which the fuel supply system includes a fuel rail for pressurised fuel supply to one or more fuel injectors to the combustion chamber(s), the fuel rail also 5 providing pressurised fuel for the bypass fuel system.

16. A method of reducing turbo-lag in an internal combustion engine, the engine comprising one or more combustion chambers, a first air inlet system; a fuel supply system; an 10 exhaust gas system; a turbocharger including in the exhaust gas system an exhaust-driven impeller and in the air inlet system an impeller-driven compressor; a second air inlet system for providing bypass air upstream of the impeller and which bypasses the combustion chamber(s); and an air pump; 15 wherein the method comprises the steps of: i) aspirating the combustion chamber(s) with inlet air from the first air inlet system; 20 ii) delivering combustion fuel to the combustion chamber(s) using the fuel supply system; iii) venting exhaust gas from the combustion chamber(s) via the exhaust gas system; iv) using said exhaust gas to drive the impeller and hence the compressor to boost the air charge to the combustion chamber(s); 30 v) using the air pump to pump bypass air through the second air inlet system towards the exhaust gas system upstream of the impeller;

- 23 vi) using the fuel supply system to deliver fuel into the bypass air separately of the delivery of fuel to the combustion chamber(s); and vii) igniting the bypass air: fuel mixture downstream of the air pump and upstream of the impeller to create a boost to the exhaust gas and thereby boost the impeller speed and reduce turbo lag.

17. A method of reducing turbo-lag in an internal combustion engine, substantially as herein described, with reference to or as shown in the accompanying drawings.

17. An internal combustion engine, substantially as herein described, with reference to or as shown in the accompanying drawings. 15

18. A method of reducing turbo-lag in an internal combustion engine, substantially as herein described, with reference to or as shown in the accompanying drawings.

Amendments to the claims have been filed as follows Claims 19 1. An internal combustion engine, comprising: - a plurality of combustion chambers; 5 - a first air inlet system for aspirating the combustion chamber(s) with inlet airs - a fuel supply system including a combustion fuel system for delivering fuel to the combustion chamber(s); - an exhaust gas system including an exhaust manifold for 10 venting exhaust gas from the combustion chamber(s); - a turbocharger for boosting the air charge to the combustion chamber(s), said turbocharger including in the exhaust gas system downstream of the exhaust manifold an exhaust-driven impeller and in the air inlet system an 15 impeller-driven compressor for compressing inlet air; - a second air inlet system for providing bypass air upstream of the impeller and which bypasses the combustion chamber(s); - an air pump arranged to pump bypass air from the second air inlet system towards the exhaust gas system) wherein the fuel supply system includes a bypass fuel system for delivering fuel into the bypass air upstream. of the exhaust manifold and the engine further comprises a source of ignition downstream of the air pump which during engine 25 operation serves to ignite the bypass air/fuel mixture downstream of the air pump and upstream of the impeller to create a boost to the exhaust gas and hence a boost to the impeller speed.

30 2. An internal combustion engine as claimed in Claim 1, in which the second air inlet system draws air independently of the first air inlet system.

2< 3. An internal combustion engine as claimed in Claim 1, in which the second air inlet system is an air bypass between the first air inlet system and the exhaust gas system, and 5 the an air pump is arranged to pump bypass air from the first air inlet system through the air bypass towards the exhaust gas system.

4. An internal combustion engine as claimed in Claim 3, 10 further comprising an engine control unit arranged to control both the operation of the air pump and the fuel supply system so as to control independently the delivery of fuel to the combustion chamber(s) and the bypass air.

15 5. An internal combustion engine as claimed in Claim 4, further comprising an exhaust gas sensor for sensing the composition of the exhaust gas the engine control unit being responsive to said sensed exhaust gas composition to control an air:fuel ratio for the bypass air and the bypass fuel.

6. An internal combustion engine as claimed in any of Claims 3 to 5' -in which-the---first air supply system includes an intercooler downstream of the compressor for cooling and raising the density of compressed inlet air, the air bypass 25 being downstream of the intercooler.

8. An internal combustion engine as claimed in any preceding claim, in which the air pump is driven by an

Zb electric motor.

9. An internal combustion engine as claimed in any preceding claim, in which the second air supply system 5 includes a mixing chamber upstream of the exhaust manifold into which the bypass fuel and bypass air are delivered and combusted, the mixing chamber having a combustion gas outlet into the exhaust manifold.

10 10. An internal combustion engine as claimed in Claim 9, in which the mixing chamber is formed from a ceramic material.

11. An internal combustion engine as claimed in Claim 9 or Claim 10, in which the mixing chamber includes a catalyst to 15 facilitate combustion of the bypass fuel with the bypass air.

12. An internal combustion engine as claimed in any of Claims 9 to 11, in which the mixing chamber includes a matrix into which the bypass fuel and bypass air are channelled, the 20 matrix being heated by the combustion of the bypass fuel in the bypass air.

13. An internal combustion engine as claimed in any of Claims 1 to 8, in which the ignition source is the exhaust 25 manifold which in use is heated by exhaust from the combustion chamber(s) above the flash point of the bypass fuel and air.

14. An internal combustion engine as claimed in any 30 preceding claim, in which the fuel supply system includes a fuel rail for pressurised fuel supply to one or more fuel injectors to the combustion chambers, the fuel rail also

*) providing pressurised fuel for the bypass fuel system.

15. A method of reducing turbo-lag in an internal combustion engine, the engine comprising a plurality of combustion 5 chambers, a first air inlet system; a fuel supply system; an exhaust gas system including an exhaust manifold; a turbocharger including in the exhaust gas system downstream of the exhaust manifold an exhaust-driven impeller and in the air inlet system an impeller-driven compressor; a second air 10 inlet system for providing bypass air upstream of the impeller and which bypasses the combustion chamber(s); and an air pump; wherein the method comprises the steps of: i) aspirating the combustion chamber(s) with inlet air from 15 the first air inlet system; ii) delivering combustion fuel to the combustion chamber(s) using the fuel supply system; 20 iii) venting exhaust gas from the combustion chamber(s) via the exhaust gas system; iv) using said exhaust gas to drive the impeller and hence the compressor to boost the air charge to the combustion 25 chamber(s); v) using the air pump to pump bypass air through the second air inlet system towards the exhaust gas system upstream of the impeller; vi) using the fuel supply system to deliver fuel into the bypass air upstream of the exhaust manifold separately of the

r r r r I ., r delivery of fuel to the combustion chamber(s); and vii) igniting the bypass air: fuel mixture downstream of the air pump and upstream of the impeller to create a boost to 5 the exhaust gas and thereby boost the impeller speed and reduce turbo lag.

16. An internal combustion engine, substantially as herein described, with reference to or as shown in the accompanying 10 drawings.