Patent Application
20100018507
This invention relates to gasoline engines. In particular, this invention relates to a fuel intake which increases the efficiency of a two stroke gasoline engine.
In two-stroke gasoline engines, the gasoline fuel is mixed with air in the carburetor and delivered to the cylinders. The fuel-air mixture is ignited in the cylinder and the energy used to provide the mechanical energy of the engine. Because of the inherent inefficiencies in the engine, the engine produces both mechanical energy and heat energy.
The carburetor is often connected to the engine via an intake manifold which communicates the fuel-air mixture from the carburetor to the engine. Often, a rubber boot is used between the engine and intake manifold to isolate the engine heat and vibration from the carburetor.
Atomized fuel contains small droplets of fuel mixed with air. Vaporized fuel contains the fuel in a gaseous state and mixed with air, a combination that usually provides superior burning properties and is more efficient in a two stroke engine.
However, delivering atomized fuel to the combustion chamber is beneficial to the cooling of the cylinder head as it absorbs heat from its surroundings as it is vaporized. Pre-heating of the atomized fuel also generally improves the burning properties of the engine.
If the fuel-air mixture enters the cylinder too hot, there is a tendency for the mixture to lose homogeneity, an effect that can negatively affect the burning of the fuel and therefore lower the efficiency of the engine.
There are several techniques known in the prior art to heat the incoming fuel-air mixture using secondary sources of heat. For example, U.S. Pat. No. 5,778,860 issued Jul. 14, 1998 to Garcia teaches the heating of a portion of the fuel using the ambient heat of the engine compartment. Garcia teaches heating the liquid fuel before it is atomized by the carburetor. This requires adjustments be made to the preheating when the external ambient temperature changes, such as operating the engine on hot summer days. In high outside temperatures, less preheating of the fuel is required as the incoming fuel is already partially warmed before entering the intake manifold. Using this design in cold climate conditions reduces its effectiveness because the temperature of the ambient engine compartment is cooler. This disadvantage is due to its indirect heating design, namely that heat from the engine has to heat the ambient air which in turn heats the incoming fuel-air mixture.
The elongated fuel bypass taught in U.S. Pat. No. 5,769,059 issued Jun. 23, 1998 to Wallace uses a bypass adjacent to the intake manifold to preheat the fuel mixture. It uses an elongated fuel air bypass of between three and twelve feet to vaporize the fuel air mixture, and beat from the ambient environment of the engine compartment to heat the fuel-air mixture passing through the bypass. Because the design relies on heat from the ambient environment, it uses a large surface requiring both length and a large outside diameter. This is expensive, cumbersome and requires additional compensating devices to compensate for its flaws. With the large amount of surface area, the design is subject to variations in the ambient temperature. In hot weather, it may overheat the fuel mixture. In cold weather, the elongated bypass will transfer a lot of heat through the large surface, requiring a heavier wall thickness in the bypass or a heat exchanger to improving the heating of the fuel mixture. After air supply, an injection system and a backfire safety device are other compensating devices taught for this design to work properly. Further, this design is suitable only for a four stroke engine, as its use on a two stroke engine may impair the scavenging of exhaust in the combustion chamber because of the turbulence introduced in the bypass to increase the mixing of the fuel-air mixture.
In drawings which illustrate by way of example only a preferred embodiment of the invention,
Generally, the intake tube 1 is a short straight tube connecting the carburetor directly to the engine. The thermal conductivity of the material, the length, diameter and thickness of the tube, and the thermal coupling of the intake tube 1 to the engine are selected to optimize the vaporization of the fuel-air mixture passing into the engine. Selecting the wall thickness of the tube is the preferred technique for optimizing the vaporization of the fuel-air mixture.
In the description that follows, the preferred embodiment will be described in the context of a 500 cubic centimetre (cc.) two cylinder piston ported two stroke engine with 250 cc. cylinder displacement per cylinder. However, it will be appreciated that the intake tube 1 of the invention can be used with other two-stroke engines and the invention is not intended to be limited to the particular embodiment shown and described herein by way of example.
The intake tube 1 is illustrated in
Disposed at an intermediate portion of the intake tube 1, preferably around the axial centre, is a copper oil injection tube 20 which extends through the intake tube 1 generally along a diameter (i.e. generally at the radial centre of the intake 1). The copper oil injection tube 20 may be installed substantially vertically within the intake I (when mounted) and flush with the outside diameter of the intake at the top 22. At the bottom of the intake, the injection tube 20 extends out of the intake by a short distance, for example about 0.375 inches. Alternatively, the injection tube 20 may extend only partially through the intake tube 1.
Referring to
At the bottom of the intake 24, the outside of the injection tube 20 preferably narrows as at 25 to facilitate coupling with an oil injection hose (not shown), preferably to an outside diameter of 0.125 inches to be compatible with a ⅛ inch or 3 mm oil injection hose (not shown). The oil injection hose is connected to the engine's oil injection pump (not shown). Oil can thus be pumped from the engine's oil injection pump, through the oil injection hose to the oil injection tube 20 and out the orifice 26 into the intake tube 1. It will be appreciated that providing the connection point to the oil injection hose at the bottom of the intake I is for convenience only and does not limit the positioning or orientation of the oil injection tube 20.
Referring to
The end of the intake tube 1 opposite the flange 2 has a radiused undercut 28 which reduces the outside diameter of the intake tube 1 to a diameter of about 1.5 inches. A carburetor boot 40, such as the Mikuni® VM 34 rubber carburetor boot as shown in
With reference to the above description, the following section describes how the inventor believes the invention works. However, this is only one theory which might explain the operation of the invention, and no representation is made that the operation is actually as described.
The general operation of the intake assembly I relies upon engine heat transferred by conductivity from the engine 5 to the intake tube 1 through the contact surface area between the engine 5 and the flange 2. The high thermal conductivity of the copper intake tube 1 allows the heat to transfer to the intake tube 1, exposing the fuel mixture with sufficient heat to homogenize the fuel droplets without substantially heating the fuel mixture temperature.. The length, diameter and thickness and other dimensions of the intake tube 1 are designed to vaporize substantially all of the fuel-air mixture before it enters the engine but not substantially heat the mixture. In the preferred embodiment, the primary factor is the wall thickness of the intake tube 1.
Preferably, in normal engine operation, the intake tube 1 will be substantially at the ambient temperature of the engine compartment and the fuel will be homogenized.
Further, heat from the intake tube 1, the oil injection tube 20 and the fuel-air mixture aids in the vaporization of the oil injected from the oil injection tube 20. The heat provided by the walls of the intake tube 1, the oil is at least partially vaporized and mixed with the fuel mixture. The main purpose of the oil injected into the fuel-air mixture is to lubricate the engine. In the experience of the inventor, less oil is required to lubricate an engine when the oil is vaporized.
As the atomized fuel mixture enters the intake tube 1, heat from the intake tube 1 vaporizes the mixture, especially around the circumference of the intake tube 1 interior, where the fuel mixture is in direct contact with the intake tube 1. As the fuel mixture approaches the copper oil injection tube 20, there is sufficient heat available to fully vaporize the remaining atomized fuel in the center of the intake tube 1. Further, the heat from the oil injection tube 20 itself may aid with vaporizing the fuel mixture along the axial centre of the intake tube 1. After passing the oil injunction tube 20, some heat may be transferred from the fuel mixture to the oil to vaporize the oil. It is desirable that all the heat that is transferred to the intake tube 1 be used in the vaporization process of the fuel mixture and oil, resulting in a minimal temperature increase of the fuel mixture.
In the preferred embodiment, the dimensions of the intake tube 1, including the length and thickness of the copper are designed so that the intake tube 1 remains at approximately the same temperature as the fuel-air mixture temperature entering the intake from the carburetor during most engine operating conditions.
Preferably, the fuel mixture is vaporized before the oil is introduced in the intake tube 1. In the inventor's experience, separate vaporizations of the fuel mixture and oil results in a more consistent vaporization over a variety of engine operating conditions.
The dimensions of the oil injection tube 20 are important so that the oil is not over heated. The thickness of the walls of the oil injection tube 20 and the size of the orifice 26 affect the rate at which the heat from the intake tube 1 is transferred to the injected oil. Since some heat is transferred to the oil, the viscosity of the oil is reduced and the orifice 26 may be made smaller. The size of the orifice 26 affects the rate at which oil is injected into the intake 1.
Further, the oil injection tube 20 must have a small outside diameter in relation to the inside diameter of intake tube 1, as mentioned above, so it does not cause undue turbulence in the flow of fuel mixture to the engine. Turbulence in the fuel mixture is undesirable and for two-stroke engines can interfere with the scavenging process to expel burnt fuel from the cylinder. Turbulence may cause inconsistent fuel atomization and or inconsistent control of fuel vaporization.
It will be appreciated that the use of an oil injection tube 20 may not be required in some embodiments of the invention. For example, a four stroke may not require oil injection and it is possible to pre-mix the oil with the fuel for use in a two stroke engine.
In the applicant's experience, the use of the invention in the preferred embodiment requires substantially less oil than the typical 50:1 fuel to oil mix and preferred operation uses a reduction in the oil injection ratio of approximately 35:1. The oil injection pump volume was also reduced to half from the stock 50:1.
Depending on the specific engine design, it may be necessary to modify the exhaust or ports of the engine to address overheating of the homogenized fuel mixture in the exhaust pipe before being drawn back in to the cylinder. Preferably, the exhaust ‘y’ pipe is extended between one cylinder exhaust port and the joint with the other cylinder exhausts.
Copper is used in the preferred embodiment because of its high thermal conductivity. In the preferred embodiment, tellurium copper alloy in particular is used because it is easier to machine than copper. A person skilled in the art will recognize that other metals and alloys with high thermal conductivity could be used, including plain copper.
Proper alignment of the intake tube 1 with the intake ports and the carburetor is important for smooth vibration free operation. As is known to someone skilled in the art, it may be necessary to make adjustments, including shimming and bracing, to the invention to allow vibration free operation and efficiency. Especially important to this invention is the contact between the engine 5 at the intake ports and the copper flange 2 of the intake tube 1. Proper contact is required for the thermal conductivity between the engine and the intake, therefore it is preferred that the intake ports and flange be machined flat and have a good flat surface.
Various embodiments of the present invention having been thus described in detail by way of example, it will be apparent to those skilled in the art that variations and modifications may be made without departing from the invention.
