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Title:
AN AIR-FUEL INJECTION SYSTEM FOR TWO STROKE INTERNAL COMBUSTION ENGINES
Document Type and Number:
WIPO Patent Application WO/2009/044412
Kind Code:
A3
Abstract:
A system and method can provide an air-fuel mixture to a two-stroke internal combustion engine (30). The system can include an air compressor (10). The air compressor (10) can include a compressor inlet valve (12), a compressor outlet valve (18), and a compressor piston (72). A two-stroke internal combustion engine (30) can be connected to the compressor (10). The engine can include an engine cylinder (27), an engine cylinder head (26), and an engine air-fuel inlet valve (24) at the engine cylinder head (26). A pipe (20) can communicate air and fuel between the outlet valve (18) of the compressor and the engine air-fuel inlet valve (24). An air-fuel mixture can be provided to the engine cylinder (27) through the engine air-fuel inlet valve (24), timed by the outlet valve (18) of the compressor. The engine air-fuel inlet valve (24) can be actuated by a pressure difference between the pipe (20) and the engine cylinder (27). The outlet valve (18) of the compressor is configured to be in a specified phased relationship to the compressor piston (72). The compressor piston (72) is configured to be in a specified phased relationship with the engine (30).

Inventors:
ASVATHANARAYANAN RAMESH (IN)
MARIMUTHU LOGANATHAN (IN)
Application Number:
PCT/IN2008/000640
Publication Date:
June 18, 2009
Filing Date:
October 06, 2008
Export Citation:
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Assignee:
INDIAN INST TECHNOLOGY (IN)
ASVATHANARAYANAN RAMESH (IN)
MARIMUTHU LOGANATHAN (IN)
International Classes:
F02M67/02; F02B25/00; F02M71/02
Foreign References:
DE19939898A12000-03-02
US5809949A1998-09-22
EP0044738A11982-01-27
Attorney, Agent or Firm:
MURALIDHAR, Khadilkar, S. et al. (Kini House6/39 Jungpura B, New Delhi 4, IN)
Download PDF:
Claims:

CLAIMS

1. A system comprising:

an air compressor, comprising a compressor inlet valve, a compressor outlet valve, and a compressor piston;

a two-stroke internal combustion engine, connected to the compressor, the engine including an engine cylinder, an engine cylinder head, and an engine air-fuel inlet valve at the engine cylinder head; and

a pipe, communicating air and fuel between the outlet valve of the compressor and the engine air-fuel inlet valve, wherein an air-fuel mixture is provided to the engine cylinder through the engine air-fuel inlet valve, timed by the outlet valve of the compressor, wherein the engine air-fuel inlet valve is actuated by a pressure difference between the pipe and the engine cylinder, wherein the outlet valve of the compressor is configured to be in a specified phased relationship to the compressor piston, and wherein the compressor piston is configured to be in a specified phased relationship with the engine.

2. The system of Claim 1 , wherein the air-fuel mixture is provided to the engine cylinder such that less short circuiting of fuel in the engine cylinder occurs during a scavenging cycle as compared to a like engine having the air-fuel mixture provided via a manifold.

3. The system of Claim 1 , wherein the compressor comprises a pin on the compressor piston, wherein the pin configured to actuate the compressor outlet valve.

4. The system of Claim 3, wherein the pin on the compressor piston is configured to open the compressor outlet valve when the compressor piston is near top dead center (TDC).

5. The system of Claim 4, wherein the pin on the compressor piston is configured to open the compressor outlet valve when the compressor piston is in a range that is between about 15 degrees before top dead center (TDC) to about 60 degrees before TDC of the engine.

6. The system of Claim 1 , wherein the compressor is configured to provide pressurized air at a pressure that is within a range between about 2 bars x and about 7 bars to atomize the fuel.

7. The system of Claim 1 , wherein the compressor output valve is configured to open at a specified crank angle of the compressor, wherein the crank angle is in a range that is between top dead center (TDC) and about 60 degrees before TDC of the compressor.

8. The system of Claim 1 , wherein a swept volume of a cylinder of the air compressor is in a range that is between about 2% and about 20 % of a swept volume of the engine cylinder.

9. The system of Claim 1 , wherein the air compressor is connected to the engine in a specified phased relationship by at least one of a pulley system, a gear, or a cam.

10. The system of Claim 1 , wherein the engine air-fuel inlet valve comprises a poppet valve.

11. The system of Claim 10, wherein the poppet valve is configured to inject the air-fuel mixture in a direction that is substantially opposite to a direction of scavenging gases moving through the engine cylinder, and in a direction such that that a combustible mixture is formed in a spark zone provided by a spark plug on the engine cylinder head.

12. The system of claim 1 , wherein the compressor inlet valve comprises a reed valve configured to receive, for introduction into a cylinder of the compressor, air and a liquid lubricant.

13. The system of claim 1 , comprising at least one of a carburetor or a low pressure injector, operable in a range of about 2 bar to about 5 bar, having an output configured to supply fuel to the pipe.

14. A timing air-fuel inlet valve assembly for a two-stroke internal combustion engine, comprising:

an auxiliary cylinder to an engine, the cylinder including a piston, an input port, and a output port, wherein the piston includes a piston pin, located at an end face portion of the piston and configured to actuate the output port;

a valve body, at or near the output port;

a movable valve, configured to move within a tapered collar from a resting position at which the movable valve provides a substantially airtight seal with the collar, the movable valve comprising a distal end in mutual cooperation with the pin of the piston end to actuate the movable valve; and

wherein the piston pin is configured to trigger the distal end of the movable valve to open the output port of the cylinder when, in a piston cycle, the piston nears top dead center (TDC).

15. The valve assembly of Claim 14, wherein the movable valve comprises at least one of a pin valve, a spring-loaded valve, or a solenoid valve.

16. The valve assembly of Claim 14, wherein valve assembly is configured to open the output port of the cylinder at a plurality of crank angles and speeds of the engine.

17. The timing valve of Claim 14, wherein the piston pin is configured to trigger the movable valve to open when the piston of the auxiliary cylinder in a range between about 0 degrees and about 60 degrees before TDC of the auxiliary cylinder, and to close when the piston of the auxiliary cylinder is in a range that is between about 0 degrees and about 60 degrees after TDC of the auxiliary cylinder.

18. A method comprising:

cyclically compressing air in a phased relationship with a two-stroke engine;

initiating release of the compressed air into a pipe at a specified phase of at least one of the engine and a compressor;

mixing fuel into the compressed air in the pipe; and

actuating an engine inlet valve and, using a pressure difference between the compressed air and an engine cylinder pressure, opening the valve and injecting an air-fuel mixture into the cylinder.

19. The method of Claim 18, comprising directing the injected air-fuel mixture in a direction generally toward a spark zone and generally opposing a direction of scavenging air flow during a scavenging cycle of the two-cycle engine while an exhaust port of the engine is still open.

20. The method of Claim 18, wherein injecting the air-fuel mixture into the cylinder comprises reducing a short circuiting as compared to providing the air- fuel mixture via a manifold or transfer duct from a crank case of the engine.

Description:

"AN AIR-FUEL INJECTION SYSTEM FOR TWO STROKE INTERNAL

COMBUSTION ENGINES"

TECHNICAL FIELD

This document relates generally to a two-stroke internal combustion engine, and more particularly, but not by way of limitation, to a method and apparatus for an air-fuel mixture injection system that can be configured to be adapted to an application.

BACKGROUND

Two-stroke engines are simple in construction, cheap to produce and maintain, and have a high power to weight ratio. They also have lower friction losses than four-stroke engines with similar power outputs. Two-stroke engines can be preferred over four-stroke engines in vehicular applications such as mopeds, small scooters, snowmobiles, or hand-held power tools. Further, in developing countries like India, a large number of two-stroke engines are used in three- wheeled vehicles in urban areas for transportation. Two-stroke engines in these applications have high fuel consumption and high levels of hydro-carbon (HC) and carbon monoxide (CO) emissions.

Two-stroke engines have a problem of short-circuiting when fuel is injected into the cylinder, such as during the scavenging phase. In such short- circuiting, the fresh fuel that is injected into the cylinder via an input port does not stay in the cylinder long enough to be burned, but instead rather quickly exits the output port of the cylinder along with the exhaust. Short-circuiting decreases fuel efficiency. For example, because of short circuiting, fuel efficiency of a two- stroke internal combustion engine can decrease by 25% to 40%, and the

emission of un-bumt HCs increases. Use of electronically controlled manifold fuel injection systems, which are popular in four-stroke engines, have not significantly improved fuel economy or reduced HC emission in two-stroke engines.

OVERVIEW/SUMMARY

The present inventors have recognized, among other things, the limited potential of certain approaches that attempt to reduce fuel short circuiting by injecting fuel through the cylinder barrel or the transfer port. The present inventors have also noted that, in order to completely avoid short-circuiting, an approach can be to inject fuel into the cylinder after the exhaust ports close. The present inventors have also recognized that certain approaches to avoiding short-circuiting can include high pressure injection, air-assisted injection using electrp/iic controls, or using pump-less systems. However, the present inventors have recognized that it would still be advantageous to provide an inexpensive and easy-to-implement approach that can reduce, minimize, or avoid short- circuiting.

Accordingly, an embodiment of the present system and method can provide an air-fuel mixture to a two-stroke internal combustion engine. The system can include an air compressor. The air compressor can include a compressor inlet valve, a compressor outlet valve, and a compressor piston. A two-stroke internal combustion engine can be connected to the compressor. The engine can include an engine cylinder, an engine cylinder head, and an engine air-fuel inlet valve at the engine cylinder head. A pipe can communicate air and fuel between the outlet valve of the compressor and the engine air-fuel inlet valve. An air-fuel mixture can be provided to the engine cylinder through an

engine air-fuel inlet valve, timed by the outlet valve of the compressor. The engine air-fuel inlet valve can be actuated by a pressure difference between the pipe and the engine cylinder. The outlet valve of the compressor is configured to be in a specified phased relationship to the compressor piston. The compressor piston is configured to be in a specified phased relationship with the engine.

In Example 1 , a system can comprise an air compressor, comprising a compressor inlet valve, a compressor outlet valve, and a compressor piston. A two-stroke internal combustion engine can be connected to the compressor. The engine can include an engine cylinder, an engine cylinder head, and an engine air-fuel inlet valve at the engine cylinder head. A pipe can communicate air and fuel between the outlet valve of the compressor and the engine air-fuel inlet valve. An air-fuel mixture is provided to the engine cylinder through the engine air-fuel inlet valve, timed by the outlet valve of the compressor. The engine air-fuel inlet valve is actuated by a pressure difference between the pipe and the engine cylinder. The outlet valve of the compressor is configured to be in a specified phased relationship to the compressor piston. The compressor piston is configured to be in a specified phased relationship with the engine.

In Example 2, the system of Example 1 can optionally be configured such that the air-fuel mixture is provided to the engine cylinder such that less short circuiting of fuel in the engine cylinder occurs during a scavenging cycle as compared to a like engine having the air,fuel mixture provided via a manifold.

In Example 3, the system of any one or more of Examples 1-2 can optionally be configured such that the compressor comprises a pin on the compressor piston, wherein the pin configured to actuate the compressor outlet valve.

In Example 4, the system of any one or more of Examples 1-3 can optionally be configured such that the pin on the compressor piston is configured to open the compressor outlet valve when the compressor piston is near top dead center (TDC).

In Example 5, the system of any one or more of Examples 1-4 can optionally be configured such that the μin υn the compressor piston is configured to open the compressor outlet valve when the compressor piston is in a range that is between about 15 degrees before top dead center (TDC) to about 60 degrees before TDC of the engine.

In Example 6, the system of any one or more of Examples 1-5 can optionally be configured such that the compressor can provide pressurized air at a pressure that is within a range between about 2 bars and about 7 bars to atomize the fuel.

In Example 7, the system of any one or more of Examples 1-6 can optionally be configured such that wherein the compressor output valve is configured to open at a specified crank angle of the compressor, wherein the crank angle is in a range that is between top dead center (TDC) and about 60 degrees before TDC of the compressor.

In Example 8, the system of any one or more of Examples 1-7 can optionally be configured such that a swept volume of a cylinder of the air compressor is in a range that is between about 2% and about 20 % of a swept volume of the engine cylinder.

In Example 9, the system of any one or more of Examples 1-S can optionally be configured such that the air compressor is connected to the engine

in a specified phased relationship by at least one of a pulley system, a gear, or a cam.

In Example 10, the system of any one or more of Examples 1-9 can optionally be configured such that the engine air-fuel inlet valve comprises- a poppet valve.

In Example 11 , the system of any one or more of Examples 1-10 can optionally be configured such that the poppet valve is configured to inject the air- fuel mixture in a direction that is substantially opposite to a direction of scavenging gases moving through the engine cylinder, and in a direction such that that a combustible mixture is formed in a spark zone provided by a spark plug on the engine cylinder head.

In Example 12, the system of any one or more of Examples 1-11 can optionally be configured such that the compressor inlet valve comprises a reed valve configured to receive, for introduction into a cylinder of the compressor, air and a liquid lubricant.

In Example 13, the system of any one or more of Examples 1-12 can optionally comprise at least one of a carburetor, or a low pressure injector, operable in a range of about 2 bar to about 5 bar, having an output configured to supply fuel to the pipe.

" Example 14 includes a timing air-fuel inlet valve assembly for a two-stroke internal combustion engine. In this example, the timing air-fuel inlet valve assembly can include an auxiliary cylinder to an engine. The cylinder can include a piston, an input port, and a output port. The piston can include a piston pin, located at an end face portion of the piston and configured to actuate the output port. A valve body can be at or near the output port. A movable valve

can be configured to move within a tapered collar from a resting position at which the movable valve can provide a substantially airtight seal with the collar. The movable valve can comprise a distal end in mutual cooperation with the pin of the piston end to actuate the movable valve. The piston pin can be configured to trigger the distal end of the movable valve to open the output port of the cylinder when, in a piston cycle, the piston nears top dead center (TDC).

In Example 15, the valve assembly of Example 14 can optionally be configured such that the movable valve comprises at least one. of a pin valve, a spring-loaded valve, or a solenoid valve.

In Example 16, the valve assembly of any one or more of Examples 14-15 optionally can be configured to open the output port of the cylinder at a plurality of crank angles and speeds of the engine.

In Example 17, the valve assembly of any one or more of Examples 14-16 can optionally be configured such that the piston pin is configured to trigger the movable valve to open when the piston of the auxiliary cylinder , in a range between about 0 degrees and about 60 degrees before TDC of the auxiliary cylinder, and to close when the piston of the auxiliary cylinder is in a range that is between about 0 degrees and about 60 degrees after TDC of the auxiliary cylinder.

Example 18 describes a method. In this example, the method can i comprise cyclically compressing air in a phased relationship with a two-stroke engine, initiating release of the compressed air into a pipe at a specified phase of at least one of the engine and a compressor, and mixing fuel into the compressed air in the pipe. An inlet valve can be actuated, using Ia pressure

difference between the compressed air and an engine cylinder pressure, for opening the valve and injecting an air-fuel mixture into the cylinder.

in Example 19, the method of Example 18 can optionally comprise directing the injected air-fuel mixture in a direction generally toward a spark zone and generally opposing a direction of scavenging air flow during a scavenging cycle of the two-cycle engine while an exhaust port of the engine is still open.

In Example 20, the method of any one or more of Examples 18-19 can optionally be performed such that injecting the air-fuel mixture into the cylinder comprises reducing a short circuiting as compared to providing the air-fuel mixture via a manifold or transfer duct from a crank case of the engine.

This Overview/Summary is intended to provide an overview of the subject matter of the present patent application. It is not intended to provide an exclusive or exhaustive explanation of the invention. The detailed description is included to provide further information about the present patent application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a functional block diagram of an example of the present air-fuel injection system.

FIG. 2 illustrates an example of portions of a process using the present air-fuel inject-on system shown in FIG. 1.

FIG. 3 illustrates a cross-section of an example of the present pin valve mounted on a cylinder head of a compressor.

FIG. 4'A illustrates a cross section of an example of the present poppet valve injector.

FIG. 4B illustrates a diagram ofip ' ositrøπing of the present poppet vaive on a cylinder head of a cylinder of a two-stroke engine, such as with respect to a spark plug and scavenging air flow.

FIG. 5 is a photograph that illustrates an example of formation of a cloud air-fuel mixture using an example of portions of the present system such as shown and described with respect to FIG. 1.

FIG. 6A is a chart depicting an example of injection timing of the air-fuel mixture demonstrating optimum output power as achieved using an example of the present system such as shown and described with respect to FIG. 1.

FIG. 6B is a chart depicting an example of injection timing of the air-fuel mixture demonstrating optimum efficiency as achieved using an example of the present system such as shown and described with respect to FIG. 1.

FIG. 7A is a chart depicting an example of hydrocarbon (HC) emission using injection timing with a timing valve opening time at 25% throttle as achieved using an example of the present system such as shown and described with respect to FIG. 1.

FIG. 7B is a chart depicting an example of the carbon monoxide (CO) emission using injection timing with a timing valve opening time at 25% throttle as achieved using an example of the present system such as shown and described with respect to FIG. 1

FIG. 8A is a chart comparing (1) an example of the output power provided by a two-stroke commercially available engine using manifold injection of gasoline compared to (2) an example of the output power provided by the same

engine.tegnfigtired using the present air-fuel mixture injection scheme such as illustrated in the example of FlG. 1.

FIG. 8B is a chart comparing (1) an example of the hydrocarbon (HC) emission provided by a two-stroke commercially available engine using manifold injection of gasoline compared to (2) an example of the HC emission provided by the same engine configured using the present air-fuel mixture injection scheme such as illustrated in the example of FIG. 1.

FIG. 9A is a chart comparing (1) an example of the carbon monoxide (CO) emission vs. power output provided by . a two-stroke commercially available engine using manifold injection of gasoline compared to (2) an example of the CO emission vs. power output provided by the same engine configured using the present air-fuel mixture injection scheme such as illustrated in the example of FIG. 1.

FIG. 9B is a chart comparing (1) an example of the equivalence ratio vs. power output provided by a two-stroke commercially available engine using manifold injection of gasoline compared to (2) an example of the equivalence ratio vs. power output provided by the same engine configured using the present air-fuel mixture injection scheme such as illustrated in the example of FIG. 1.

FiG. 10 is a chart comparing (1) an example of the nitric oxide (NO) emission vs. power output provided by a two-stroke commercially available engine using manifold injection of gasoline compared to (2) an example of the NO emission vs. power output provided by the same engine configured using the present air-fuel mixture injection scheme such as illustrated in the example of FIG. 1.

DETAlLED DESCRiPTlOM

FIG. 1 illustrates a functional block diagram of an example of the present air-fuel injection system 5. In this example, the air-fuel injection system 5 can include a compressor 10 (e.g., a 25 cc air-compressor, or the like), a two-stroke internal combustion (IC) engine 30 (e.g., a 150 cc IC engine, or the like), a pulley drive 31 , a compressor inlet valve 17 (e.g., a reed valve, other one-way valve, or the like), a compressor outlet valve 18 (e.g., a piston-pin driven movable valve, other one-way valve, or the like), a fuel introducer 22 (e.g., a carburetor or low pressure fuel injector), a high pressure line 20 (als^o referred to as a "high pressure pipe", e.g., a pipe, tube, or other conduit), and an engine air-fuel inlet valve 24 (e.g., a poppet valve, or other one-way valve).

In an illustrative example, but not by way of limitation, a 150 ce two-stroke IC engine 30 can be used, such as described for illustrative purposes in Table 1. In an example, the IC engine need not be air-cooled, and other implementations can also vary from the illustrative example described in Table 1.

Table 1 : Illustrative Description of Two-Stroke IC Engine Characteristics

FiG. 1 shows an example in which the compressor 10 can be connected to a two-stroke internal combustion engine 30 by a toothed pulley and belt drive 31 (e.g., a 1:1 drive). The drive 31 maintains a proper specified phasing between the compressor 10 and the IC engine 30 (e.g., a 1 :1 phase relationship between compressor cycles and engine cycles). In an example, the compressor 10 can be mounted on the IC engine 30. In an example, the specified phasing between the compressor 10 and the IC engine 30 can be controlled by a chain, by a cam, or by any other suitable technique of maintaining the phase relationship. In the example of FIG. 1, the compressor 10 comprises a coπipressor cylinder body 12, and a distal compressor cylinder head 13. A compressor piston can be located within the cylinder body 12. In the example of FiG. 1, the cylinder head 12 can include a compressor input port 14 and a compressor output port 16. The input port 14 can include or be connected to a compressor inlet valve 16. In an example, the compressor inlet valve 16 admits a mixture of air and a lubricator into the cylinder body 12 via the input port 14 in the cylinder head 12. In an illustrative example, the valve 17 can include a reed valve. Other types of openings or valves can be used, such as to admit the mixture of air and lubricant. For example, a set of holes distributed about the circumference of the cylinder head 12 can be used to admit the mixture of air and lubricant. Further, other types of valves can be used for valve 17, such as a spring loaded valve, a solenoid valve, or any other type of one way valve that can be appropriately timed. In an example, the valve 17 can be adjustably timed to open at a specified engine or compressor crank angle, which timing may be controllably varied at different operating speeds of the engine 30 or the compressor 10. The compressor output port 16 can include or be connected to a compressor outlet valve, such as a pin valve 18, which can include a valve that is actuated by a pin on an end face of the compressor piston that is located

within the cylinder body 12. Connected to the pin valve 18 is a high pressure pipe 20. in the example of FIG. 1 , the high pressure pipe 20 is connected to a fuel source 22, such as a low pressure injector or a carburetor, which introduces fuel into the high pressure pipe 20. The high pressure pipe 20 can connect the low pressure injector or other fuel source 22 to a poppet valve injector or other engine air-fuel inlet valve 24 that is attached to the cylinder head 26 at a distal end of the cylinder body 27 of the two-stroke internal combustion engine 30.

In an example, the engine air-fuel inlet valve 24 includes a poppet valve injector that can be positioned on the cylinder head 26 of the engine 30 near a spark plug. In an illustrative example, for a cylinder having a 57 mm bore, a distance between the spark plug and the poppet valve can be about 50 mm. In an example, the poppet valve injector can be placed such as shown in FIG. 4B, e.g., on the same side of the cylinder body 27 as an exhaust port. In another example, the poppet valve injector can be placed on an opposite side of the cylinder body 27 from the exhaust port. In an example, the poppet valve injector can be spring-loaded such that, in operation, the poppet valve injector can open and close in response to a pressure differential between the cylinder and the high pressure pipe 20. The spring of the poppet valve injector can be configured to inhibit or prevent unwanted leakage from the cylinder, such as from pressure differentials across the poppet valve injector other than the actuating pressure differential created by the compressor 10 to actuate the poppet valve injector. As explained herein, the poppet valve injector can inject the air-fuel mixture from the high pressure pipe 20 into an engine cylinder in cooperation with the compressor outlet valve, such as to inhibit, reduce, or minimize short-circuiting of the injecting air-fuel mixture out the exhaust port during the scavenging cycle of the two-cycle engine. Moreover, the poppet valve injector can be oriented with

respect to the engine cylinder head 26 such that an air-fuel mixture is injected in a direction opposite to a scavenging gas flow and toward a spark zone, so as to improve the atomization or combustion of the air-fuel mixture within the cylinder.

FIG. 2 describes an example of portions the present process 50 that includes injecting an air-fuel mixture into the two-stroke internal combustion engine 30 of FIG. 1. At 51, the process 50 begins. At 52, air (and optionally, a lubricant) can be injected into the input port 14 of the compressor 10, such as via the reed valve 17. The amount of lubricant mixed with the air is, in an example, enough to lubricate the compressor 10. In an example, the amount of lubricant can range from about 1-2% of the fuel to be injected. In another example, the amount of lubricant can be about 0.5% of the amount of fuel to be injected. After the mixture of air and lubricant enters the cylinder of the compressor 10, it can be compressed.

At 54, the compressor piston 72 (shown in FIG. 3) cycles until the compressor piston 72 reaches near top dead center (TDC). At 56, the exhaust port 16 (shown in FIG. 3) on compressor 10 is appropriately timed to open and exhaust compressed air . In an example, such timing can be obtained using a pin valve 18 that opens the exhaust port 16 when the compressor piston 72 nears TDC. In an example, this occurs when the outlet valve on the compressor 10 opens at a specified engine crank angle that is between about 15 degrees before BDC of the engine to about 60 degrees before BDC of the engine. Thus, the phasing between the engine 30 and the compressor 10 can be such that the outlet valve on the compressor opens at between about 15 degrees and about

60 degrees before the engine piston reaches its BDC and starts moving toward its TDC. This angle can be varied based on operating condition (e.g., speed, throttle, or the like). At 58, the compressed air can be ejected into the high

pressure line 20. In an example, the compressed air in the high pressure line 20 can be pressurized to a pressure that is between about 2 bar and about 5 bar.

At 60, fuel (e.g., gasoline or the like) can be injected by the fuel introducer 22 into the high pressure line 20. This can include, for example, using a carburetor, a low pressure gasoline injector, or the like. As the fuel is metered into the high pressure line 20, the high pressure air (e.g., at above 2 bar presssure, such as at about 2-5 bar pressure) atomizes the fuel. In an example, the fuel can be injected just before the pressurized air reaches the fuel introducer 22. In an example, the fuel can be injected (e.g., by a fuel pump or an engine control unit) into the airflow of the pressurized air in the high pressure line 20. For instance, the fuel can be pressurized at a pressure that is in a range between about 2 bar to about 20 bar, when injected to mix with the pressurized air in the high pressure line 20. The pressurized air atomizes the fuel, such as to create a rich air-fuel mixture. The duct shape fuel introducer 22, the pressure value of the compressed air, and the fuel metering rate into the high pressure line can affect the degree of atomization that occurs.

At 62, the pressure of the rich air-fuel mixture in the high pressure line 20 (e.g., 2-5 bar pressure) opens the engine air-fuel inlet valve 24, which can be a poppet valve injector. At 64, the rich air-fuel mixture can be injected, via a cylinder head, into a cylinder of a two-stroke IC engine 30. As the rich air-fuel mixture enters the cylinder of the internal combustion engine 30, the rich air-fuel mixture atomizes into fine droplets, such as because of the compressed air injection and because of an opposing directional gaseous flow within the cylinder during its scavenging cycle. This helps form a combustible mixture inside the cylinder, such as in a spark zone where it can be ignited. The process 50 can be repeated as shown by flow line 66 shown in the example of FIG. 2.

Among other things, the process 50 allows the timing of the opening of the pin valve 18 to be made as late as possible, such that fuel short-circuiting is reduced or eliminated. This allows enough time for mixture preparation in the cylinder. By reducing the fuel short-circuiting, more fuel is available for > combustion. This can significantly reduce fuel consumption (e.g., by about 10- 20%). This can also significantly reduce hydrocarbon (HC) emission (e.g., by about 50%).

FIG. 3 illustrates a cross-section of an example of the present pin valve 18 mounted on the cylinder head 16 of a compressor 10 such as shown in FIG. 1. In this example, the compressor 10 also includes an input valve such as a reed valve 310, such as to admit air (and optionally a lubricant) into the cylinder body 12 of the compressor 10. In this example, the pin valve 18 can be configured as a timing Valve that can determine when compressed air is allowed to exit the compressor 10. In an example, the timing valve can include a valve body 300. A spring 302 mutually cooperates with a movable valve 304, which can include a tapered or conically moving part. A collar 306 can be configured to accept the movable valve 304. In an example, the spring 302 can be floating (e.g., untethered). The collar 306 and the spring 302 can be configured to maintain the position of the movable valve as being seated against the collar 306 until actuated. The timing valve can be attached to the output port 16 of the compressor cylinder body 12. The compressor cylinder body 12 can house a piston 72 having a pin 308, such as can be located on an end face of the piston 72. Near top dead center (TDC), the pin 308 engages or otherwise mutually cooperates with the movable valve to actuate its opening by compressing the spring 302. This ejects compressed air through the output port 16 of the cylinder body 12 of the compressor 10. The pin valve 18 provides a convenient and

effective timing valve. However, in various examples, the pin valve 18 can be substituted or augmented by one or more of a spring-loaded valve, a solenoid valve, or other type of timing valve or the like that can be connected to the outlet port of the compressor.

FIG. 4A illustrates a cross-section of an example of the present poppet valve assembly that can be used as an engine air-fuel inlet valve 24 mounted on the cylinder head 26 of the engine 30 shown in FIG. 1. In the example of FIG. 4A, the poppet valve assembly can include a movable poppet valve 400, a valve body 402A-B, a spring 404, and a spring retainer 406. In an example, the poppet valve 400 can be configured within the valve body 402 to create a substantially air-tight and leak-proof seal, by holding the poppet valve 400 seated . against a collar 408 until actuated by the compressor 10, and then re-seating the poppet valve 400 after such actuation. In an example, the spring retainer 406 is in mutual cooperation with the high pressure line 20 and in contact with the spring 404. The spring 404, in turn, can be connected to the movable poppet valve 400. The spring retainer 406 can hold the poppet valve 400 closed against the collar 408 until a specified pressure is reached in the high pressure line 20 (e.g., a pressure that is between about 2 bars and about 5 bars). When the pressure reaches the specified threshold value, the spring retainer 406 pushes down on the spring 404. This, in turn, causes the poppet valve 400 to move away from the collar 408 of the valve body 402. The angle of the interface between the head of the poppet valve 400 and the collar 408 of the valve body can be configured to help improve the distribution of the rich air-fuel mixture into the cylinder. This can enhance mixing of the atomized air-fuel mixture in the cylinder body 27 of the engine 30. Furthermore, the poppet valve assembly shown in FIG. 4A can inhibit or prevent back-flow of the air-fuel mixture from

within the cylinder body 27 back toward or into the high pressure line 20. In an example, the poppet valve assembly can optionally include water or other liquid ports 41 OA-B, such as for liquid-cooling the poppet valve assembly. This can help promote longevity of one or more of the components of the poppet valve assembly, such as the spring 404.

The poppet valve assembly can serve as an engine air-fuel inlet valve 24 to inject the air-fuel mixture into the cylinder body 27 of the engine 30. The poppet valve assembly shown in FIG. 4A can be positioned near the spark plug such that a combustible mixture is present near the spark plug at the time of ignition, and a suitable mixture that can burn with low emissions is present elsewhere, in an example, the orientation of the fuel injector can be such as shown in the example of FIG. 4B. The exact location of the poppet valve can change, such as depending on the size of the engine cylinder. In an example, the poppet valve can be located such that the spray direction is generally opposite the exhaust port. Even though, in an example, the air-fuel mixture is injected during the period when the exhaust port is open, short-circuiting of the air-fuel mixture can be reduced or minimized. By placing the poppet valve pointing in a direction generally opposite to the exhaust port, a long path is created for the injected air-fuel mixture to take to reach the exhaust port. Therefore, even if the exhaust port is open when the air-fuel mixture is initially injected into the engine cylinder, the exhaust port is closed by the time the air- fuel mixture travels the path from the input port to the exhaust port. Thus, such positioning of the poppet valve can further reduce short-circuiting of the air-fuel mixture during the scavenging cycle. FIG. 5 shows a photographic view of the air-fuel spray cloud from the poppet valve. In the example of FIG. 5, the photo is taken outside of the engine cylinder.

FIG. 6A is a chart depicting an example of injection timing of the air-fuel mixture demonstrating optimum output power as achieved using an example of the present system such as shown and described with respect to FIG. 1. In this example, the timing valve opening time was taken at 25% throttle. In this example, the best power output was obtained with a timing valve opening time that was about 60 degrees before Bottom Dead Center (bBDC) of the engine piston for a variety of air-fuel ratios as shown.

FIG. 6B is a chart depicting an example of injection timing of the air-fuel mixture demonstrating optimum efficiency as achieved using an example of the present system such as shown and described with respect to FIG. 1. In this example, the timing valve opening time was taken at 25% throttle. In this example, the best efficiency was obtained with a timing valve opening time that was about 30 degrees before Bottom Dead Center (bBDC) of the engine piston for a variety of air-fuel ratios as shown.

FIG. 7A is a chart depicting an example of hydrocarbon (HC) emission using injection timing with a timing valve opening time at 25% throttle as achieved using an example of the present system such as shown and described with respect to FIG. 1. In this example, the timing valve opening time was taken at 25% throttle. In this example, the lowest HC emission was observed with a timing valve opening time that was about 30 degrees before Bottom Dead Center (bBDC) of the engine at an air-fuel ratio of about 20, as shown.

FIG. 7B is a chart depicting an example of the carbon monoxide (CO) emission using injection timing with a timing valve opening time at 25% throttle as achieved using an example of the present system such as shown and described with respect to FIG. 1. In this example, the timing valve opening time

was taken at 25% throttle. In this example, the lowest CO emission was observed with a timing valve opening time that was about 60 degrees before Bottom Dead Center (bBDC) of the engine for a variety of air-fuel ratios as shown.

FIG. 8A is a chart comparing an example of (1) the brake thermal efficiency provided by an example of a two-stroke commercially available engine using conventional manifold injection of gasoline to (2) an example of the brake thermal efficiency of the same engine configured in accordance with the present air-fuel mixture injection system, such as shown and described with respect to FIG. 1. In both examples, brake thermal efficiency was measured at an engine speed of 3000 rpm. FIG. 8A demonstrates that the present air-fuel injection system is better than the typical manifold injection at all outputs. Without being bound by theory, this is believed to result because of the reduction in the amount of fuel short-circuited. FIG. 8A shows the manifold injection yielded a brake thermal efficiency of about 25.5%, whereas the air-fuel mixture injection system yielded a brake thermal efficiency of about 23%. It is believed that optimizing the air-fuel mixture injection system may even allow the brake thermal efficiency of the present system to approach the brake thermal efficiency of a four-stroke engine (e.g., about 28%).

FIG. 8B is a chart comparing an example of (1) hydrocarbon emission provided by an example of a two-stroke commercially available engine using conventional manifold injection of gasoline to (2) an example of the hydrocarbon emission provided by an example of same engine configured using the present air-fuel mixture injection system, such as shown and described with respect to FIG. 1 . FIG. 8B demonstrates that the conventional manifold system can produce hydrocarbon emission as low as about 1360 ppm. However, the

present air-fuel mixture injection system can further reduce hydrocarbon emission to a level of about 460 ppm. At high power output conditions, the drop in hydrocarbon emission can be significant. Without being bound by theory, it is believed that this is because short circuiting of the fresh air-fuel mixture (e.g., fresh charge) is reduced or minimized. Further, reductions in hydrocarbon emission can be achieved, such as by reconfiguring the poppet valve injector to produce a finer atomization, reshaping the combustion chamber to produce a more conducive air movement pattern, optimizing the location of the poppet valve and the air pressure, optimizing the size and shape of the poppet valve, optimizing the location at which fuel is fed into the high pressure line 20, or the like.

FIG. 9A is a chart comparing (1) an example of the carbon monoxide (CO) emission vs. power output provided by a two-stroke commercially available engine using manifold injection of gasoline compared to (2) an example of the CO emission vs. power output provided by the same engine configured using the present air-fuel mixture injection scheme such as illustrated in the example of FIG. 1. In general, the present air-fuel mixture injection scheme exhibited more CO emission for a given power output. Without being bound by theory, it is believed that this is because there is not enough time for mixing in the present air-fuel mixture injection scheme as compared to a manifold injection arrangement in which pre-mixing occurs inside of a carburetor.

FIG. 9B is a chart comparing (1) an example of the equivalence ratio vs. power output provided by a two-stroke commercially available engine using manifold injection of gasoline compared to (2) an example of the equivalence ratio vs. power output provided by the same engine configured using the present air-fuel mixture injection scheme such as illustrated in the example of FIG. 1. In

general, the present air-fuel mixture injection scheme exhibited a lower equivalence ratio for a given power output, meaning that most of the fuel sent into the engine is retained, rather than short-circuited. Without being bound by theory, it is believed that this indicates that the present air-fuel mixture injection scheme reduces or inhibits fuel short-circuiting as compared to a manifold injection arrangement.

FIG. 10 is a chart comparing (1) an example of the nitric oxide (NO) emission vs. power output provided by a two-stroke commercially available engine using manifold injection of gasoline compared to (2) an example of the NO emission vs. power output provided by the same engine configured using the present air-fuel mixture injection scheme such as illustrated in the example of FIG. 1. In general, the present air-fuel mixture injection scheme exhibited higher NO emission for a given power output. Without being bound by theory, it is believed that this is because the present air-fuel mixture injection scheme runs leaner, and therefore, traps more air, and produces more NO (comparable to a four-stroke engine) as compared to a manifold injection arrangement. The NO emission can be controlled (to a reasonable extent), such as by adjusting spark timing, but such reduction in NO emission may also somewhat reduce fuel efficiency. ,

To recap, the above description indicates that an example of a technical effect of the present techniques that using direct injection of fuel through pressurized air assistance for a two stroke engine can decrease unbumed hydrocarbon emissions and increase fuel efficiency.

ADDITIONAL NOTES

The above detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show, by way of illustration, specific embodiments in which the invention can be practiced. These embodiments are also referred to herein as "examples." Such examples can include elements in addition to those shown and described. However, the present inventors also contemplate examples in which only those elements shown and described are provided.

All publications, patents, and patent documents referred to in this document are incorporated by reference herein in their entirety, as though individually incorporated by reference. -In the event of inconsistent usages between this document and those documents so incorporated by reference, the usage in the incorporated reference(s) should be considered supplementary to that of this document; for irreconcilable inconsistencies, the usage in this document controls.

In this document, the terms "a" or "an" are used, as is common in patent documents, to include one or more than one, independent of any other instances or usages of "at least one" or "one or more." In this document, the term "or" is used to refer to a nonexclusive or, such that "A or B" includes "A but not B," "B but not A," and "A and B," unless otherwise indicated. In the appended claims, the terms "including" and "in which" are used as the plain-English equivalents of the respective terms "comprising" and "wherein." Also, in the following claims, the terms "including" and "comprising" are open-ended, that is, a system, device, article, or process that includes elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim. Moreover,

in the following claims, the terms "first," "second," and "third," etc. are used merely as labels, and are not intended to impose numerical requirements on their objects.

The above description is intended to be illustrative, and not restrictive. For example, the above-described examples (or one or more aspects thereof) may be used in combination with each other. Other embodiments can be used, such as by one of ordinary skill in the art upon reviewing the above description. The Abstract is provided to comply with 37. C. F. R. §1.72(b), to allow the reader to quickly ascertain the nature of the technical disclosure. Also, in the above Detailed Description, various features may be grouped together to streamline the disclosure. This should not be interpreted as intending that an unclaimed disclosed feature is essential to any claim. Rather, inventive subject matter may lie in less than all features of a particular disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment. The scope of the invention should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.