TECHNICAL FIELD

The subject matter described herein, in general, relates to a fuel injection system for a two-stroke diesel engine, and in particular, relates to a common-rail direct injection system for a two-stroke diesel engine.

BACKGROUND

Conventionally, internal combustion (IC) engines are used in industrial, vehicular and marine applications. IC engines are typically classified into two main categories namely two stroke and four stroke. A two stroke engine completes one revolution of the crank in one combustion cycle as opposed to a four-stroke engine, in which the crank takes two revolutions for completing one combustion cycle, the four strokes being intake, compression, combustion, and exhaust strokes. IC engines are further classified based on the type of fuel used for combustion, for example, as diesel or petrol engines.

In diesel engines, fuel is injected either directly into the combustion chamber or into pre-combustion chamber by a fuel injection system. The type of fuel injection system used directly affects the efficiency of an engine. Typical fuel injection systems used are of two types, namely indirect injection and direct injection.

In IC engines with an indirect injection system, fuel is delivered into a pre-combustion chamber where combustion begins and then partially burnt products of combustion spread into a main combustion chamber. The fuel pump and injectors on early diesels were completely mechanical, and though precision machined and ruggedly built, the working pressure of the fuel system was not sufficiently high enough to render a sustained and well-defined spray pattern of fuel. Further, such engines often delivered a shot of fuel with a poor and ill-defined spray pattern that was either too rich (most often)
or too lean, that resulted in either a rich belch of sooty black smoke, or insufficient power and a struggling vehicle. Traditional mechanical fuel injection systems, direct / indirect are less efficient and are considered inadequate for delivering environment friendly, fuel efficient, less noisy, smooth and compact engine for the desired power output.

Advances in fuel injection systems enable metering of accurate fuel quantity at the precise timing and for precise duration at different speeds and loads. Such modem systems enable injection of fuel with desired fuel spray characteristics and with the desired rate to obtain optimum rate of heat release. These advances have been achieved with modem Common Rail Direct Injection (CRDI) systems where the pressure generation and injection at different speeds and loads are decoupled.

At present, diesel IC engines in four-wheeled vehicles widely use CRDI injection system. However, the use of diesel engines for two/three-wheeled vehicles is limited only to certain parts of the world especially for off-road applications and non-commuter segment applications even though diesel provides better fuel efficiency than petrol and two-stroke engines are capable of more power generation than four-stroke engines. The reasons which hampered the growth of diesel engines in two/three-wheeled vehicles include large size engine for desired power output, high vibrations, high Nox emissions, low power-to-weight ratio and high noise levels of such engines. Further, strict emissions norms and high maintenance cost associated with this engine type also hampered the growth of such an engine.

Experience of passenger cars have shown that CRDI-based diesel engines give good power output with performance and emissions similar to gasoline engines. The CRDI based four wheeled vehicles generate lesser vibrations, have lower emissions and lower noise levels, and provide increased efficiency as compared to traditional indirect and direct injection based diesel engines. However, using the CRDI technology, though possible for small bore for two/three wheelers application, imposes certain challenges due to space constraints and compactness requirement of the engine assembly in the absence of possibilities for turbo-charging such engines. Two and three wheeled vehicles require a more compact yet light weight engine design as compared to a four wheeled vehicle.

Also, a bulky engine would make balancing of the vehicle difficult. High drive-train oscillations coupled with high noise of these type of engines provide further challenges for implementing such technology for these applications. Further, packaging of the engine in a vehicle must be done in such a way that the vehicle looks appealing to a consumer.

As two/three wheelers are the most common modes of transportation for a large percentage of people across the world, thus, it is desirable to have two-stroke diesel engines which are fuel efficient, compact, affordable, produce less vibrations and easy to implement in two/three wheelers.

SUMMARY

The subject matter as described herein relates to a two-stroke diesel engine-based vehicle having a mechanical unit pump common rail system (MUPCR) for fuel injection. In this system, fuel is fed by gravity through a micro-fuel filter to a fuel pump from a fuel tank of the vehicle. The fuel pump is driven by a cam on a crankshaft. In one implementation, the cam operates with the same speed as that of the crankshaft, thus driving the fuel pump at the speed of the crankshaft. The fuel pump pressurizes the fuel received from the fuel tank to a much higher pressure as compared to conventional fuel injector systems. The pressurized fuel from the fuel pump is then fed to an accumulator, commonly known as fuel rail, which is mounted at an appropriate location or can be cast integral with the high pressure pump. The fuel inside the fuel rail is maintained at a constant high pressure. The high pressure fuel from the fuel rail is delivered to an injector, which then sprays the fuel into a combustion chamber. The injector sprays the fuel through multiple orifices of a nozzle such that a nearly horizontal spray pattern is achieved.

Mechanical Unit Pump Common Rail (MUPCR) fuel injection systems, as already mentioned, provide many advantages. In addition to those, the proposed MUPCR fuel injection system has been designed such that the spray is well atomized at the nozzle exit and the plume traverses the small bore combustion chamber for maximum air utilization with improved rate of heat release characteristics that deliver smooth, high performance with low emissions and high efficiency.

These and other features, aspects, and advantages of the present subject matter will become better understood with reference to the following description and appended claims. This summary is provided to introduce a selection of concepts in a simplified form. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

BRIEF DESCRIPTION OF DRAWINGS

The above and other features, aspects, and advantages of the subject matter will become better understood with regard to the following description, appended claims, and accompanying drawings where:

Fig. 1 illustrates a cross sectional view of an exemplary MUPCR fuel injection system of a two-stroke single cylinder diesel engine.

Fig. 2(a) illustrates an exemplary fuel rail connected for use in the exemplary two-stroke single cylinder diesel engine of Fig. 1.

Fig. 2(b) illustrates the exemplary injector mounted on the cylinder head of the exemplary two stroke single cylinder diesel engine of Fig. 1.

Fig. 3 illustrates a block diagram of an exemplary MUPCR system.

DETAILED DESCRIPTION

The subject matter described herein is directed to a Mechanical Unit Pump Common Rail (MUPCR) fuel injection system for two/three wheeled vehicles more particularly to a two stroke diesel engine based two/three wheeled vehicles. The present subject matter proposes a fuel injection system that overcomes aforementioned challenges and provides better efficiency, less emission levels, less fuel consumption, and lesser vibrations.

Fig 1 illustrates a cross sectional view of an exemplary MUPCR fuel injection system 100 of an exemplary two stroke single cylinder diesel engine. The MUPCR fuel injection system 100 includes a fuel pump assembly (or fuel pump) 102 that delivers fuel to a fuel rail 104 connected to an injector 106 for injecting fuel into a combustion chamber 108 through a nozzle 110. The engine combustion system includes a naturally aspirated, direct injection, steroidal shaped quiescent combustion chamber 108 with a radial squish flow at its Top Dead Centre (TDC)

The fuel is fed to the fuel pump 102 from a fuel tank (not shown) through a filter (micro fuel filter), which prevents abrasive materials from entering the fuel injection system 100. The fuel filter is positioned in the compartment below the fuel tank and above the fuel pump 102 inlet. Also, the fuel filter is equipped with mechanism for water separation.

In one embodiment, the fuel is fed by gravity through the fuel filter to fuel pump 102 from the fuel tank. The fuel pump 102 is designed to facilitate self-venting even with gravity fed fuel from the fuel tank after prolonged gap between usage of vehicle . The fuel pump 102 also facilitates self venting in-situations when engine is started after service when the fuel is completely drained from the fuel tank. Current conventional fuel systems for diesel three-wheelers use feed pump at the suction side of high pressure of fuel pump.

The fuel pump 102 gets the drive from an eccentric cam located on a crankshaft 112. The cam and crankshaft arrangement is configured such that the fuel pump 102 operates at the speed of the crankshaft 112, as opposed to at half the speed of the crankshaft in conventional systems. The operation and sizing of the fuel pump 102 is such that pressure generation is completely decoupled at different speeds and loads as compared to conventional fuel pumps. In the fuel injection system for four stroke, the fuel pump would get the derive from the gearshift with conventional 1:2 ratio.

In operation, the fuel pump 102 receives fuel from the fuel tank and compresses fuel to high pressure and delivers the pressurized fuel to the fuel rail 104. The high pressure fuel from the fuel rail 104 is then sent to the injector 106. The injector 106 includes the nozzle 110 with the desired configuration to deliver well-atomized high pressure spray plume for maximum air-utilization without wetting the walls. In one implementation, the injector 106 is a solenoid actuated injector that is activated when a programmed input is received.

The nozzle 110 injects the high pressure fuel into the combustion chamber 108 through multiple orifices

The well-atomized high pressure fuel spray injected from the multiple small orifices of the nozzle 110 is assisted by air-flow from the radial squish at the TDC. The radial squish flow at the TDC helps in good mixture preparation and also helps in achieving more efficient fuel combustion. The excess fuel from the injector 106, and the rail 104 is sent back to the fuel tank. The fuel tank is equipped with a level sensor and connections for return of overflow from the injector 106 and the fuel rail.104.

Fig. 2(a) illustrates an exemplary fuel rail for use in the exemplary two-stroke single cylinder diesel engine of Fig. 1. The fuel rail 104 receives the high pressure fuel from the fuel pump 102 and acts as a reservoir for the high pressure fuel to ensure that the high pressure fuel is instantly available during combustion. Further, the fuel rail 104 has a pressure sensor 208 and a high pressure valve 210, which ensures that a constant high pressure inside the fuel rail 104 is maintained even while injecting the fuel in the combustion chamber 108. The high pressure fuel is then delivered to the injector 106 through a high pressure pipe 202. The injector 106 is clamped vertically at the centre of a cylinder head 204 with the help of a clamp plate 206.

Two and three-wheeled vehicles with the typical power output requirement need small-sized engines which are lightweight and compact as such engines have high power-output from small-engines. The diesel two-stroke engine in discussion has small bore cylinders, typically ranging from 60mm to 80mm, as compared to typical four wheeler engine. The small bore size for two-stroke diesel engine with quiescent combustion system poses challenge for the implementation of a MUPCR fuel injection system. The challenge is overcome by mounting the fuel rail 104 on the cylinder head 204 along the length of the vehicle and by mounting the injector 106 vertically at the centre of the cylinder head 204.

A second challenge for implementation of such systems is regarding the safety for use of high-pressure system in two-wheeler application. The challenge is overcome by orienting the fuel rail 104 in such a way that it provides easy venting near the high pressure valve 210. The high pressure fuel lines from the fuel pump 102 to the fuel rail

104 and from the fuel rail 104 to the injector 106 are on the same side of vehicle. The safety of the high pressure connections from the fuel pump 102 to the fuel rail 104 and from the fuel rail 104 to the injector 106 is ensured by providing a shield (not shown in the fig.) around the high pressure system.

Fig. 2(b) illustrates the exemplary injector mounted vertically on the two stroke single cylinder diesel engine of Fig. 1. The nozzle 110 of the injector 106 has multiple small orifices (Not Shown). The orifices are arranged along a diameter of the nozzle 110 in such a way that the angle between the centers of the nozzle orifices is from 160" to 180°.

The orifices being small in size result in injection of a small quantity of the high pressure fuel, as required by a small bore engine. The constant high pressure is maintained inside the fuel rail 104 due to the sizing of the volume on high pressure side of pump. Also, the constant quantity of fuel, pumped by the fuel pump 102 due to direct transmission of power from the crankshaft to the fuel pump helps in maintaining the constant high pressure inside the fuel rail 104.

The high pressure fuel from the nozzle 110 is injected into the combustion chamber 108 from each of the orifices. The high pressure fuel sprayed from each of the orifices forms a small spray cone. If a line is drawn from the centre of each of the spray cones, the entire spray pattern comes out to be nearly horizontal or perpendicular to bore axis with an angle of about 160" to 180°. Therefore, the vertical position of the injector 106, along with the described arrangement of the orifices, provides a nearly horizontal spray pattern.

The near horizontal spray is important to ensure that the spray plume is precisely spaced between the cylinder head wall and piston crown, when injection is done near the TDC. The injection plume due to the described geometry, oriented nearly horizontal or perpendicular to the bore axis helps in achieving the desired output with low emissions and good efficiency.

Further, the injector 106 is capable of multiple injections per stroke for spraying the fuel into the combustion chamber 108. The high pressure fuel is injected for short durations during the multiple injections into the combustion chamber 108. The short multiple injections generate a smoother cycle during the combustion process, thus reducing excess noise and vibrations. In addition, the clamping of the injector 106 on to the cylinder head 204 with the help of a clamp plate 206 enables easy removal of the injector 106.

Fig. 3 illustrates a functional block diagram for an exemplary MUPCR system. In the exemplary MUPCR system 300, fuel is fed through gravity from a fuel tank 302 to a fuel pump 304. The fuel pump 304 pressurizes the fuel. The pressurized fuel from the fuel pump 304 is then fed to a fuel rail 306 mounted on a cylinder head of the engine. The fuel inside the fuel rail 306 is maintained at a constant high pressure. The high pressure fuel from the fuel rail 306 is delivered to an injector 308 through a high pressure pipe, which then sprays the fuel into a combustion chamber 310. The excess fuel from the injector 308 and the rail 306 is sent back to the fuel tank through 312.

MUPCR fuel injection systems, as already mentioned, provide many advantages. In addition to those, the proposed MUCPR fuel injection system also provides an injector having a nozzle with multiple small sized orifices, low through flow and wide spray plume for good atomization and spray penetration to maximize air-utilization.

In one embodiment, the fuel injection system is used for a two-stroke multi-cylinder engine. electronic fuel pump. For example, an inlet metering valve, a storage means or an integral accumulator rail for high pressure fuel may be used instead of a separate fuel rail with a pressure sensor and the separate fuel rail may or may not include a high pressure valve for pressure control in the storage means.

In yet another embodiment, the fuel injection system can be used for a single or multi-cylinder four-stroke engine. For example a four stroke engine with drive arrangement from the gearbox input shaft with drive ratio of 1:2, for use in a two/three-wheeled vehicle. The previously described versions of the subject matter and its equivalent thereof have many advantages, including those which are described above. The fuel injection system described herein provides increased fuel efficiency, low vibrations, and fewer emissions.

Although the subject matter has been described in considerable detail with reference to certain preferred embodiments thereof, other embodiments are possible. As such, the spirit and scope of the appended claims should not be limited to the description of the preferred embodiment contained therein.

I/We claim:

1. A two-stroke compression ignition engine (200) for a two-wheeled or three-wheeled vehicle, the two-stroke compression ignition engine (200) comprising:

at least one cylinder (205);

a piston (215) movably disposed inside the cylinder (205); and a crankshaft (210) operably connected to the piston (215); characterized in that,

a fuel injection system (105) provided to inject pressurized fuel into the cylinder (205), wherein the fuel injection system (105) comprises,

a fuel filter (112) connected to a fuel tank (110);

a fuel pump (115) to pressurize fuel received from the fuel tank (110) via the fuel filter (112), wherein the fuel pump (115) is mounted on a crankcase (220);

an accumulator (120) to receive the pressurized fuel from the fuel pump (115); and

at least one injector (125) to receive the pressurized fuel from the accumulator (120) for injecting the pressurized fuel in the cylinder (205).

2. The two-stroke compression ignition engine (200) as claimed in claim 1, wherein the accumulator (120) is a fuel rail, and wherein the fuel rail is positioned such that a longitudinal axis of the fuel rail is substantially parallel to a longitudinal axis of the vehicle.
3. A two-stroke compression ignition engine (200) for a two-wheeled or three-wheeled vehicle, the two-stroke compression ignition engine (200) comprising:

at least one cylinder (205);

a piston (215) movably disposed inside the cylinder (205); and a crankshaft (210) operably connected to the piston (215); characterized in that,

a fuel injection system (105) provided to inject pressurized fuel into the cylinder (205), wherein the fuel injection system (105) comprises,

a fuel pump (115) to pressurize fuel received from a fuel tank (110), wherein the fuel pump (115) is mounted on a crankcase (220);

an accumulator (120) to receive the pressurized fuel from the fuel pump (115), wherein the accumulator (120) is substantially parallel to a longitudinal axis of the vehicle; and

at least one injector (125) to receive the pressurized fuel from the accumulator (120) for injecting the pressurized fuel in the cylinder (205).

4. The two-stroke compression ignition engine (200) as claimed in claim 3, wherein the two-stroke compression ignition engine (200) further comprises a fuel filter (112) to receive fuel from the fuel tank (110) for filtering the received fuel and to deliver the filtered fuel to the fuel pump (115).

5. The two-stroke compression ignition engine (200) as claimed in any of the claims 1 or 3, wherein the fuel pump (115) is disposed below a fuel tank (110) such that the fuel from the fuel tank (110) is delivered to the fuel pump (115) by gravity feed.

6. The two-stroke compression ignition engine (200) as claimed any of the claims 1 or 3, wherein the cylinder (205) has a bore size ranging from about 60 mm to about 110 mm.

7. The two-stroke compression ignition engine (200) as claimed in any of the claims 1 or 3, wherein the fuel pump (115) is driven mechanically by the crankshaft (210) through

a cam mechanism, and wherein the cam mechanism includes a cam mounted on the crankshaft (210).

8. The two-stroke compression ignition engine (200) as claimed in any of the claims 1 or 3, wherein the accumulator (120) comprises a pressure sensor (325) and a pressure regulator valve (330).

9. The two-stroke compression ignition engine (200) as claimed in any of the claims 1 or 3, and wherein the fuel pump (115) includes a metering valve and the accumulator (120) includes a pressure sensor (325).

10. The two-stroke compression ignition engine (200) as claimed in any of the claims 1 or 3, wherein the accumulator (120) is integrated with the fuel pump (115).

11. The two-stroke compression ignition engine (200) as claimed in any of the claims 1 or 3, wherein the injector (125) is mounted on a cylinder head (305) through a clamping arrangement (340), such that a longitudinal axis of the injector (125) is aligned to a central axis of the cylinder head (305).

12. The two-stroke compression ignition engine (200) as claimed in any of the claims 1 or 3, wherein the fuel pump (115) and the accumulator (120) are disposed on a same side of the two-stroke compression ignition engine (200).

13. The two-stroke compression ignition engine (200) as claimed in any of the claims 1 or 3, wherein the accumulator (120) is mounted on a cylinder head (305).

14. The two-stroke compression ignition engine (200) as claimed in any of the claims 1 or 3, wherein the accumulator (120) is mounted on a cylinder block.

15. The two-stroke compression ignition engine (200) as claimed in any of the claims 1 or 3, wherein the injector (125) comprises a plurality of orifices, arranged radially, to inject fuel in a combustion chamber (130) such that the injected fuel has a substantially disc shaped spray-pattern.

16. The two-stroke compression ignition engine (200) as claimed in any of the claims 1 or 3, wherein the fuel tank (110) includes a level sensor.

17. A small bore two-stroke compression ignition engine (200) comprising:
at least one cylinder (205);

a piston (215) movably disposed inside the cylinder (205); and a crankshaft (210) operably connected to the piston (215); characterized in that,

a fuel injection system (105) provided to inject pressurized fuel into the cylinder (205), wherein the fuel injection system (105) comprises,

a fuel filter (112) connected to a fuel tank (110) to filter fuel received from the fuel tank (110) ;

a fuel pump (115) to pressurize the filtered fuel received from the fuel filter (112);

an accumulator (120) to receive the pressurized fuel from the fuel pump (115); and

at least one injector (125) to receive the pressurized fuel from the accumulator (120) for injecting the pressurized fuel in the cylinder (205).