WO1992016725A1

WO1992016725A1 - Apparatus regulating exhaust flow to increase back pressure in an internal combustion engine

Info

Publication number: WO1992016725A1
Application number: PCT/US1992/002118
Authority: WO
Inventors: Ralph A. Moody, Jr.; Ralph A. Moody, Iii
Original assignee: Moody Ralph A Jr; Moody Ralph A Iii
Priority date: 1991-03-18
Filing date: 1992-03-13
Publication date: 1992-10-01
Also published as: AU1584092A

Abstract

The internal combustion engine (10) includes a fuel delivery system (200) and an exhaust system having an apparatus (44) for regulating exhaust flow to increase engine back pressure. In response to regulated exhaust flow and increased engine back pressure, the fuel delivery system (200) is controlled to decrease fuel flow resulting in increased fuel efficiency of the engine and decreased exhaust emissions. A forced air induction system such as a turbocharger (80) or supercharger may also be used in conjuction with the engine (10). In preferred embodiments, the exhaust flow regulating apparatus (44) is either a fixed cross-sectional area orifice or a variable cross-sectional area orifice.

Description

/ APPARATUS REGULATING EXHAUST FLOW

TO

INCREASE BACK PRESSURE

IN AN INTERNAL COMBUSTION ENGINE

Background of the Invention

Internal combustion engines are widely used to provide power for vehicles and machinery, and therefore, it is desirable to design these engines so that fuel consumption and emissions are reduced.

Air flow through conventional diesel internal combustion engines is not controlled and exhaust flow is generally increased by designing these engines with reduced exhaust restrictions. Air flow through conventional gasoline engines is controlled by restrictions in the induction side which create lower than wide open throttle combustion pressures resulting in combustion efficiency losses under normal operation. Prior art teaches that internal combustion engine efficiencies are improved by reducing exhaust system restrictions. In a Society of Automotive Engineers article titled "The Influence of the Exhaust Back Pressure of a Piston Engine on Air Consumption, Performance, and Emissions", January 8-12, 1973, the authors showed that engine air consumption responds to variation of the ratio of absolute exhaust back pressure to absolute inlet manifold pressure with a strong dependence on engine speed, and that exhaust back pressure affects performance and lowers some exhaust emissions. The authors, however, did not investigate how fuel efficiency is affected when exhaust flow- is regulated to increase engine back pressure while at the same time reducing fuel flow.

Summary of the Invention

The internal combustion engine of the invention includes a fuel delivery system and an exhaust system having an apparatus for regulating exhaust flow through the engine to increase engine back pressure. In response to regulated exhaust flow and increased engine back pressure, the fuel delivery system is controlled to decrease fuel flow resulting in increased fuel efficiency. Reduced exhaust emissions also result. A forced air induction system such as a turbocharger or supercharger may also be used in conjunction with the engine.

In general, the apparatus for controlling exhaust flow and increasing engine back pressure is any restriction positioned within the exhaust system of either a diesel or gasoline (spark ignition) internal combustion engine. In one embodiment the apparatus is a venturi system having a large opening tapering to a smaller opening that allows exhaust to flow from the large opening through the smaller opening. Alternatively, the exhaust flows through a venturi system having an opening formed by a fixed side and a movable side adjustable at various engine operating parameters by an actuating system to establish a desired increase in back pressure.

The internal combustion engine of the invention directly contradicts the prior art in that back pressure is increased resulting in increased fuel efficiency. The advantages of the internal combustion engine of the invention are that fuel efficiency is increased because induction side losses of the gas engine can be reduced, the dynamic combustion pressures of both diesel and gas engines are increased, exhaust flow in both diesel and gas engines is controlled, and when utilized in conjunction with a forced air induction system such as a turbocharger or supercharger, the invention eliminates the need for and efficiency losses of a dump valve or wastegate valve that is normally required for forced air induction system overpressure protection. Brief Description of the Drawings

Fig. 1 is a perspective view of one embodiment of the internal combustion engine of the invention;

Fig. 2 is a cross-sectional view of apparatus for regulating exhaust flow to increase engine back pressure having a large opening tapering to a smaller opening;

Fig. 3 is a cross-sectional view of apparatus having a variable orifice for adjustably regulating exhaust flow to increase engine back pressure; Fig. 4 is a cross-sectional view taken along line 4-4 of the Fig. 3 apparatus;

Fig. 5 is a perspective view of the internal combustion engine of the invention showing a turbocharger connected to the exhaust system; Fig. 6 is a side view of the turbocharger shown in Fig. 5;

Fig. 7 is a front view with parts broken away from the turbocharger shown in Fig. 5;

Fig. 8 is an alternate perspective view showing a controllable fuel delivery system;

Fig. 9 is a graph showing intake manifold boost pressure as a function of RPM;

Fig. 10 is a graph showing exhaust manifold back pressure as a function of RPM; and Fig. 11 is a graph showing the ratio of boost pressure to back pressure at maximum acceleration conditions expressed in gauge pressures as a function of RPM.

Description of the Preferred Embodiments As shown in Fig. 1, an internal combustion engine 10 includes a cylinder head 12, intake manifold 14, exhaust manifold 16 and a controllable fuel delivery system 200 as shown in Fig. 8. The exhaust manifold 16 includes a pair of hollow spaced legs 18 and 20 connected to the cylinder head 12 by plates 22 and fasteners 24. Alternatively, plates 22 can be welded to the cylinder head 12 or be cast integrally with the cylinder head 12 with the prime consideration being that whatever mode of connection is used the connection should be substantially airtight. The free ends of legs 18 and 20 merge at 26 and 28 respectively, preferably in a smooth curvilinear manner, into a conduit passageway 30 disposed parallel to and spaced from the cylinder head 12. The free end of the conduit 30 terminates at an exhaust section 32, this section preferably being a smooth curved section, to which a mounting flange 34 is secured. The flange 34 removably supports an exhaust pipe 36 having an inlet 38 terminating in a flange 40 complementally fastened to the flange 34 by nuts and bolts 42 or similar fasteners. The controllable fuel delivery system 200 as shown in Fig. 8 comprises a fuel tank 137, fuel line 143, transfer fuel pump 142, fuel line 141, fuel filter 140, fuel line 139, fuel flow control lever 160, conventional rotary style fuel injection pump 133, injector lines 135, fuel injectors 134, return fuel line 138 from the fuel injectors 134, and return fuel line 136 from the fuel injection pump 133. Fuel flows from the fuel tank 137, to the transfer fuel pump 142, through the filter 140 to the fuel injection pump 133. Rate of fuel flow from the fuel injection pump 133, via lines 135 to the fuel injectors 134, is controlled by the fuel flow control lever 160. Residual fuel that is not injected into the engine is then returned to the fuel tank 137 via the return lines 136 and 138. The purpose for the return lines 136 and 138 is twofold. First, the return lines 136 and 138 allow for pump and injector cooling, especially under low load or idling conditions, and second, they allow for venting of unwanted gases that may accumulate in the system. The fuel flow spray pattern of the controllable fuel delivery system 200 may be a cone shaped fuel flow spray pattern.

It has been found that by regulating the exhaust flow exiting the engine to increase engine back pressure, air flow entering the engine can be controlled, and engine efficiency will be significantly improved when fuel flow is also reduced. Exhaust emissions will be significantly reduced as compared with conventional diesel and gas internal combustion engines. As shown in Fig. 2, this result is obtained by placing apparatus for controlling exhaust flow to increase engine back pressure within the exhaust system. A venturi system 44 is placed between exhaust section 32 of the conduit passageway 30 and the inlet 38 of the exhaust pipe 36. The venturi system 44, in its simplest form, comprises a funnel-like member 46 having a large opening 48 tapering to a smaller opening 50. A flange 52 disposed about the opening 48 is removably secured between exhaust section flange 34 and inlet flange 40 by fasteners 42 for keeping the venturi system 44 in position. The venturi system 44 may also be formed as an integral part of exhaust section 32 of conduit 30 or of the inlet 38 of the exhaust pipe 36. Exhaust flows from the large opening 48 through the smaller opening 50, thus regulating exhaust flow to increase engine back pressure. Operation of the internal combustion engine 10 incorporating the fixed venturi system 44 of Fig. 2 is identical to the operation of existing internal combustion engines commonly used in vehicles. The fixed venturi system 44 can also be incorporated into engines, such as industrial engines, operating under constant loads.

Alternatively, as shown in Figs. 3 and 4, a venturi system 44 is constructed as a variable cross-sectional area venturi system which can be utilized in engines, such as automobile engines, operating under a range of dynamic loads. Exhaust section 32 of conduit 30, shown in Fig. 1, transitions from a round to rectangular shape at section 56 terminating at rectangular section 58 having a rectangular flange 60. The variable venturi system 44 is positioned at the rectangular inlet 62 of exhaust pipe 64, such rectangular inlet 62 having a rectangular inlet flange 66 connected to rectangular flange 60 by nuts and bolts 68. The variable venturi system 44 comprises a fixed converging side 70, and a moveable side 72, which rotates with a shaft 74 movable by an arm 76 having a hole 78 for connection to an actuating device (not shown) . In addition to increasing engine back pressure and reducing fuel flow, the variable venturi system 44 of the invention may be used as the engine's main control, thus eliminating the induction side throttling device currently required for operation of non-diesel engines. Rudimentary operation of the internal combustion engine 10 incorporating the variable venturi system 44 of Figs. 3 and 4 may be accomplished by connecting the throttle pedal (not shown) to the fuel flow control lever 160 of Fig. 8 and the arm 76 of Fig. 3 by cam linkages. Actuation of the throttle pedal will change the position of the fuel flow control lever 160 and cause the arm 76 to vary the position of the movable side 72 of the venturi system 44.

In another embodiment, operation of the internal combustion engine 10 incorporating the variable venturi system 44 is effectuated by a microprocessor (not shown) that receives information from engine sensors (not shown) that measure various operating parameters. The microprocessor analyses the received information and sends optimum position output information to the fuel flow control lever 160 and arm 76 which, in turn, positions the movable side 72 of the venturi system 44. Examples of sensors that may be incorporated into the internal combustion engine 10 of the invention are sensors that measure oxygen concentration, coolant temperature, manifold air pressure, vehicle speed, throttle position, engine RPM, mass air flow, detonation (anti-knock), exhaust temperature, exhaust manifold pressure and fuel flow. The throttle pedal, connected to an input transducer (not shown), in effect, acts as the throttle position sensor. When a forced induction system such as a turbocharger is used in conjunction with the engine, as discussed below, additional sensors that measure boost pressure and turbocharger RPM may also be used for optimization of the positions of the fuel flow control lever 160 and the movable venturi system 44.

During engine idle, the variable venturi system 44 and fuel flow control lever 160 are positioned at a predetermined minimum setting. The fuel flow, controlled by the fuel flow lever 160, is continuously and automatically adjusted to maintain proper fuel mixture based on engine speed, mass air flow, and oxygen concentration sensor input. The position of arm 76, as shown in Fig. 3, is continuously and automatically adjusted for idle speed control. Because engine load may vary at idle due to accessory demands, the movable side 72 is constantly repositioned to maintain minimum idle speed. Upon desired acceleration, the throttle position sensor delivers an increasing voltage to the microprocessor which, in turn, increases the opening of the variable venturi system 44. Based on input from other operating sensors, the fuel flow control lever 160 is adjusted to regulate fuel flow resulting in an optimum air to fuel ratio. If maximum engine speed is achieved inadvertently, the microprocessor can reduce engine speed by reducing fuel flow and/or air flow by repositioning the fuel flow control lever 160 and/or the movable side 72 of the venturi system 44. In addition, if the engine is equipped with a turbocharger, the manifold air pressure sensor will supply input to the microprocessor causing the microprocessor, upon approach of maximum inlet manifold boost pressure, to begin closing the variable venturi system 44. As this action occurs, the mass air flow and the fuel flow will be reduced to maintain air to fuel ratios within an acceptable range.

Oxygen concentration sensors can also be used in conjunction with mass air flow sensors for maintaining air to fuel ratios. If the boost pressure increases beyond a desired maximum, the microprocessor will respond by initially causing the fuel flow control lever 160 and the movable side 72 to close until an acceptable air flow and manifold pressure is achieved. The engine will then return to the desired boost operating mode and optimum air flow to fuel flow will be re..ched by the gradual opening of the venturi 44 which is limited by the manifold air pressure 5 sensor. When the opening of the venturi 44 is limited, the microprocessor will also limit the opening of the fuel flow control lever 160 to maintain acceptable fuel to air ratios while controlling maximum boost pressure. It is noted that the fixed venturi system 44 of Fig. 2 cannot exceed a 10 maximum boost pressure because the smaller opening 50 is designed to control the maximum boost pressure.

At maximum deceleration, fuel flow is completely shut off by closing the fuel flow control lever 160, and the movable side 72 of the venturi system 44 is returned to a 15 preset minimum position. When the engine approaches idle speed, the fuel flow is turned back on and the engine begins operating under idle conditions. Moderate deceleration is achieved by varying the position of the movable side 72 based on input from various operating sensors including the 20 throttle position sensor. Fuel flow to fuel injectors 134, as shown in Fig. 8, is reduced proportionally as air flows are reduced by the closing of the variable venturi system 44.

As previously mentioned, the internal combustion engine 25 10 of the invention may be used in conjunction with a forced air induction system such as a turbocharger. Figs. 5 and 6 show a removable turbocharger 80 attached to the exhaust section 32 of the internal combustion engine 10 at mounting flange 34 removably supporting the turbocharger 80. A 30 housing 82 included in turbocharger 80 comprises a tangentially disposed conduit section 84 extending outwardly from the housing 82 with its free end 86 terminating at flange 88 complementally fastened to flange 34 by nuts and bolts 42 or similar fasteners. 5 Further details of the turbocharger 80 are illustrated in Figs. 5, 6 and 7, and include a totally enclosed generally cylindrical outer housing 82 having an axially disposed air inlet 90 having conduit means 91 and an axially disposed exhaust outlet 92 having conduit means 93, preferably at opposite ends thereof. An additional radially positioned opening 94 is provided adjacent to air inlet 90 and communicates therewith to convey air entering inlet 90 to the intake manifold 14 by conduit means 96 removably secured at one end to opening 94 and at the other end 98 to an opening 100 provided in the wall of intake manifold 14. The housing 82 further includes rotor housing sections 102 and 104, preferably bulbous-like, directly behind the axial disposed openings 90 and 92 and receiving rotors 106 and 108 each including a plurality of blades 110 and 112, respectively, radially disposed about a hub in conventional fashion. The rotors 110 and 112 are mounted on a common shaft mounted for rotation within housing 82. A recessed section 114 connects the rotor housing sections 102 and 104 and an oil line 116 communicating with an oil source (not shown). The oil line 116, positioned at the top of housing 82, discharges oil into the interior of housing 82 to lubricate the bearings rotatably supporting the rotor shaft. An oil return line 118 positioned at the bottom of recessed section 114 returns oil to the source.

The housing 82 is further seen to be formed of section parts to permit ready access to the interior thereof, and to this end, the rotor housing section 104 is formed with a flange 120 which is removably secured to flange 122 of recessed section 114 by a standard peripheral clamp (not shown) similar to standard peripheral clamp 130. The other flange 126 of recessed section 114 mates with flange 128 of rotor housing section 102 and is held in place by the standard peripheral clamp 130 having a nut and bolt means for holding the clamp 130 in place. A gasket 132 or the like, is used (only one being shown) to make the joints between flanges 120, 122, 126, 128 airtight.

While the weight of the turbocharger 80 is mainly supported by exhaust manifold 16 and its connection thereto, the conduit means 91, 93, and 96 associated therewith, also aid in the suspension of the turbocharger as the free ends thereof are connected to other supporting structures The free end of conduit 91 is connected to an atmospheric opening, not shown, in the vehicle or machine body, and the free end of the conduit 93 is connected to the exhaust pipe of the vehicle or machine, and the air conducting conduit 96 is connected to the intake manifold 14. The conduits 91, 93, and 96 can be made of any suitable material but it preferred that conduit 91 be made of rubber or the like of the bellows variety to facilitate connection of the conduit 91 to component parts. The air conducting conduit 96 is preferred to be constructed of metal due to temperature and pressure considerations, connected at ends 100 and 94 via rubber like hose and metal clamps to facilitate removal for inspection or repair. The exhaust conduit 93 is made of metal as it is in contact with high exhaust temperatures.

Up to this point, the operation of the turbocharger is standard in that the gases emanating from the exhaust manifold 16 at section 32 are directed against the blades 112 of rotor 108 thereby imparting rotation to the rotor 108, such rotation causing rotor 106 to rotate with the blades 110 drawing atmospheric air through conduit 91 into the rotor housing 102 from where it is discharged through conduit 96 into the intake manifold 14 to increase intake air pressure.

It is known that present day turbochargers are designed in such a manner that no consideration is given to the control and use of the air processed by the turbocharger. A dump valve or wastegate valve is associated with known turbochargers which opens to vent exhaust when too much exhaust is available in the turbocharger. This defect, as is apparent, then places additional strain on the engine in that it causes both the turbocharger and the engine to process unwanted additional volumes of exhaust that are then similarly discharged to the atmosphere via the dump valve or wastegate valve which is normally located in the exhaust manifold prior to the turbocharger. These dump valves or wastegate valves are "pop-off" relief valves actuated by the sensing of excess pressure at the intake of the engine. Upon actuation, these valves vent exhaust gases to the atmosphere, thereby preventing them from flowing through the turbocharger which would in turn generate additional intake pressures via the turbocharger function.

It has been found that by regulating the exhaust flow exiting the engine, air flow entering the engine and boost pressure produced by the turbocharger can be controlled, and the fuel efficiency of the engine or engine-turbocharger combination will be significantly improved. Exhaust emissions are also substantially reduced as compared to conventional diesel and gas engines because controlled exhaust flow and increased back pressure provide for more complete combustion.

The apparatus for regulating exhaust flow to increase engine back pressure as previously discussed and shown in Fig. 2 is incorporated into the engine-turbocharger combination to increase fuel efficiency and reduce exhaust emissions.

The first test engine-turbocharger combination was a Perkins marine diesel engine with a displacement of 108 cubic inches fitted into the chassis of a 1979 Mercury Capri. All sharp edges or contours of combustion area surfaces of the engine, such as piston top surfaces and surfaces within the cylinder head combustion chamber and preignition chamber, were slightly rounded to reduce the potential of concentrated "hotspots" during operation under leaner fuel ratios. These slight engine modifications were made to extend engine life and do not significantly alter or improve the operation of the engine. The turbocharger attached to the engine was a Rayjay turbocharger, model #3881882581. Total vehicle weight was 3,300 pounds. The fixed venturi system 44 of Fig. 2 was incorporated into the first test engine-turbocharger combination wherein the cross-sectional area of the large opening 48 was approximately 2.1 square inches, and the crosr -sectional area of the smaller opening 50 was approximately 0.44 square inches resulting in an approximate 4.7:1 cross-sectional area ratio. The fixed venturi system 44 was secured between mounting flange 34 and flange 88 as shown in Fig. 6 by nuts and bolts 42.

The first test engine-turbocharger combination having the fixed venturi system of Fig. 2 was extensively tested. Certified Environmental Protection Agency mileage and emissions tests were run with the following results:

Cold start city test:

37.10 miles per gallon

3.40 grams per mile of Carbon Monoxide 0.41 grams per mile of Hydrocarbons 1.00 grams per mile Oxides of Nitrogen

Highway test:

56.23 miles per gallon 2.10 grams per mile of Carbon Monoxide 0.33 grams per mile of Hydrocarbons 0.71 grams per mile Oxides of Nitrogen

At a steady state of 55 miles per hour 63.97 miles per gallon was achieved.

Test results, as shown by the graphs of Figs. 9 and 10, indicate that the exhaust manifold back pressure and intake manifold boost pressure can be significantly altered by the fixed venturi system 44. Increased back pressures on the engine show additional torque (horsepower) gains in the lower RPM ranges on both naturally aspirated and turbocharged engines. Horsepower gains are slightly higher in forced air induction system applications due to the added effect of slightly increased boost pressures at lower RPMs. Test results, however, indicate that engine output horsepower is not dramatically affected with back pressures exceeding 2 atmospheres, and lower RPM boost pressures can be increased while flattening the upper RPM boost pressure curve as shown in Fig. 11.

The ratio of boost pressure to back pressure varies during the several operational conditions including maximum acceleration, maximum deceleration, and idle. As shown in Fig. 11, the maximum boost pressure to back pressure ratio for the first test engine-turbocharger combination operating at maximum acceleration was approximately 0.27.

The variable orifice venturi system 44 of Figs. 3 and 4 may also be incorporated into the engine-turbocharger combination by forming the free end 86 of conduit section 84 of the turbocharger shown in Fig. 6 into a rectangular free end 86 having a rectangular flange 88 to complementally join with rectangular mounting flange 60 by nuts and bolts 68 as shown in Fig. 3. As shown in Fig. 6, the variable orifice venturi system 44 includes a fixed side 70 integrally formed with the turbocharger free end 86, movable side 72, and additional elements as previously discussed. At higher engine RPM, the orifice formed by the fixed side 70 and the movable side 72 will be larger than when operating at a lower RPM, except in the case where boost pressure begins to exceed an upper control limit predetermined by engine and turbocharger parameters. When boost pressure approaches the upper control limit the opening action of the variable orifice venturi system 44 is retarded, and is reversed as the boost pressure meets the upper control limit. This closing of the variable orifice venturi system 44 further increases back pressure on the engine, thereby reducing exhaust flow, which in turn slows the turbocharger rotation resulting in reduced boost pressure and eliminating the need for a dump or wastegate device.

What is claimed is:

Claims

1. An internal combustion engine comprising; a controllable fuel delivery system; and an exhaust system; wherein the exhaust system includes apparatus for regulating exhaust flow to increase engine back pressure; and the fuel delivery system is controlled to decrease fuel flow; whereby fuel efficiency of the engine is increased.

2. The engine of claim 1 wherein the exhaust system comprises an exhaust section; and the exhaust flow regulating apparatus comprises an orifice having a cross-sectional area smaller than the cross-sectional area of the exhaust section.

3. The engine of claim 2 wherein the ratio of the exhaust section cross-sectional area to the orifice cross-sectional area is approximately 4:1; whereby the engine back pressure is increased to approximately twice atmospheric pressure; and the fuel delivery system is controlled to reduce fuel flow by approximately thirty percent.

4. The engine of claim 1 wherein the exhaust flow regulating apparatus comprises a venturi system having a large opening tapering to a smaller opening said venturi system longitudinally positioned within the exhaust system; whereby exhaust enters the large opening and flows through the smaller opening before exiting the exhaust system.

5. The engine of claim 2 wherein the cross-sectional area of the orifice is adjustable.

6. The engine of claim 5 wherein the exhaust flow regulating apparatus comprises a venturi system having a fixed side; and a moveable side adjustable by an actuating system; whereby the movable side is adjusted for various engine operating parameters; and exhaust flows through the orifice formed by the fixed side and movable side.

7. The engine of claim 1 wherein the fuel delivery system comprises a cone shaped fuel flow spray pattern.

8. An internal combustion engine comprising; a fuel delivery system; an exhaust system; and a forced air induction system connected to the exhaust system; wherein the exhaust system includes apparatus for regulating exhaust flow to increase engine back pressure; and the fuel delivery system is controlled to decrease fuel flow; whereby fuel efficiency of the engine is increased.

9. The engine of claim 8 wherein the exhaust system comprises an exhaust section; and the exhaust flow regulating apparatus comprises an orifice having a cross-sectional area smaller than the c_.oss-sectional area of the exhaust section.

10. The engine of claim 9 wherein the ratio of the exhaust section cross-sectional area to the orifice cross-sectional area is approximately 4:1; whereby the engine back pressure is increased to approximately twice atmospheric pressure; and the fuel delivery system is controlled to reduce fuel flow by approximately thirty percent.

11. The engine of claim 8 wherein the exhaust flow regulating apparatus comprises a venturi system having a large opening tapering to a smaller opening said venturi system longitudinally positioned within the exhaust s s em; whereby exhaust enters the large opening and flows through the smaller opening before entering the turbocharger.

12. The engine of claim 9 wherein the cross-sectional area of the orifice is adjustable.

13. The engine of claim 8 wherein the exhaust flow regulating apparatus comprises a venturi system having a fixed side; and a movable side adjustable by an actuating system; whereby the movable side is adjusted for various engine operating parameters; and exhaust flows through the orifice formed by the fixed side and the movable side.

14. The engine of claim 8 wherein the fuel delivery system comprises a cone shaped fuel flow spray pattern.

15. The engine of claim 8 wherein the forced air induction system is a turbocharger.

16. The engine of claim 8 wherein the forced air induction system is a supercharger.

17. The engine of claim 1 and claim 8 wherein the engine is a diesel engine.

18. The engine of claim 1 and claim 8 wherein the engine is a gasoline (spark ignition) engine.