Two Phase Water Jet Propulsion for High-Speed Vehicles

Abstract

A water jet propulsion apparatus having an engine producing an exhaust gas, a pump driven by the engine, a nozzle in fluid communication with the pump, and an exhaust passageway communicating between the engine and the nozzle is disclosed. The exhaust passageway is connected the nozzle at a point in the nozzle where the water flow velocity is being increased, and prior to the water being expanded. By mixing the exhaust with the water while the water flow velocity is being increased, the result is a decrease the density of the mixture and an increase the total mass flow rate, thus resulting in increased thrust.

Description

STATEMENT OF GOVERNMENT INTEREST

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefore.

CROSS REFERENCE TO OTHER PATENT APPLICATIONS

None.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a water propulsion apparatus, and more particularly to a two phase water jet propulsion apparatus.

(2) Description of the Prior Art

In a typical water propulsion system, the system employs a pump connected to a nozzle. The pump, usually a high speed centrifugal water pump, is driven by an engine such as a two stroke gasoline engine, four stroke gasoline engine, or a diesel engine. The system produces thrust by first increasing velocity of the water flow, and subsequently expanding the water flow.

The engine used to pump the water in the water propulsion system generates exhaust gas and sound waves. The exhaust and sound waves are directed away from the engine compartment by an exhaust system or passageway that is connected to an exhaust port of the engine. The exhaust system is then either extended to open into the water or into the air/atmosphere. In the exhaust systems where the exhaust gas is discharged into the atmosphere, the exhaust noise creates a problem.

In the propulsion systems where the exhaust is introduced into the water, the exhaust is introduced in a low-pressure region or after the water begins to expand. While introducing the exhaust gas into the low-pressure region (after the water has expanded) reduces the sounds waves (noise level), this does not increase the efficiency of the water propulsion system or increase thrust of the water propulsion system.

Accordingly, a need exists for a water propulsion apparatus that reduces the noise level generated by the engine. The apparatus should also increase the thrust produced by the propulsion apparatus. Moreover, the apparatus should increase the overall efficiency of the propulsion apparatus.

SUMMARY OF THE INVENTION

A water propulsion apparatus is disclosed which includes a nozzle and a passageway communicating with an exhaust gas source. The nozzle includes a first region that increases the water flow velocity and a second region that subsequently expands the water, thereby producing a thrust. The passageway is connected to the nozzle at a point in the first nozzle region while the water flow velocity is being increased and prior to the second nozzle region wherein the water being expanded. In a preferred embodiment, the exhaust gas source is an engine. The engine can be a diesel engine, a gasoline engine, or a hot gas piston expander.

In a further embodiment, the present invention includes a method of increasing the thrust of a water propulsion apparatus. The method includes the steps of providing an engine that produces an exhaust gas, providing a nozzle having a first region which increases the water flow velocity and a second region which subsequently expands the water, and introducing the exhaust gas at a point in the first nozzle region while the water flow velocity is being increased and prior to the second nozzle region wherein the water is being expanded.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will be better understood in view of the following description of the invention taken together with the drawing wherein:

FIG. 1 is a schematic view of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, a water propulsion apparatus 10 in accordance with the present invention, generally includes an exhaust gas source 12, a nozzle 14 and a gas passageway 15. The exhaust gas source 12 is preferably an engine, though other gas producing sources would be recognizable to those skilled in the art. In a preferred embodiment, the engine is a diesel engine, a hot gas piston expander or a gasoline engine but not limited to, a two stroke engine or a four stroke engine.

The engine 12 drives a pump 16, typically a high-speed centrifugal pump, via a drive means 17 (such as, but not limited to, a drive shaft, transmission, drive belt, etc.) that displaces water through a water intake 18 from a water source (not shown), through the pump 16, and into the nozzle 14. As the speed of the pump 16 is increased, the amount of water displaced, the mass flow rate “M”, is increased. For a given pump speed, the pump 16 will substantially have a constant mass flow rate M.

The nozzle 14 is fluidly connected to the pump 16, and can be any nozzle known to those skilled in the art. In general, the nozzle 14 is a converging passageway wherein the nozzle diameter at region R₁ is larger than the nozzle diameter at region R₂. For a given mass flow rate M, the decrease in the diameter from R₁ to R₂ increases a velocity “V” of the water, and consequently increases the momentum of the water. As the accelerated water exits the nozzle 14 at a nozzle outlet 20, the increased momentum translates into thrust. The thrust produced by the nozzle 14 is approximated by the difference in the momentum of the water jet:

Thrust=MV_Jet−MV   (1)

where M is the mass flow rate through the system, V is the velocity of the vehicle, and V_Jet is the velocity at the nozzle which is nominally:

V_Jet=(2(P_Pump−P_Ocean)/ρ_Ocean)^1/2   (2)

where P_Pump is pressure of the pump, P_Ocean is the pressure of the ocean, and ρ_Ocean is the density of the water. This principle is well understood and known by those skilled in the art.

A result of decreasing the diameter of the passageway, and consequently increasing the water velocity, is that the pressure within the nozzle 14 at region R₁ is greater than the pressure at region R₂. This effect is reflected by Bernoulli's Equation.

In the past, most engines operate efficiently at lower exhaust back-pressures. Exhaust back-pressure is a measurement of the resistance to the flow of exhaust encountered by the engine. By and large, as engine exhaust back-pressure increases, the engine 12 requires more power to remove the exhaust gasses 15 from a combustion chamber of the engine, thus reducing the performance and efficiency. New engine designs, however, actually operate more efficiently at higher Net Mean Effective Pressure (NMEP). NMEP can be derived/defined from an expander's or engine's net power, shaft speed, and volume displaced, and is approximated by:

$\begin{array}{cc}\mathrm{NMEP}=\frac{\mathrm{NET}\mathrm{POWER}\times \mathrm{RPC}}{\mathrm{VD}\times \mathrm{RPM}}& \left(3\right)\end{array}$

The variable “RPC” (output shaft revolutions per cycle) is one for hot gas piston expanders, one for a two stroke internal combustion engine, and two for a four stroke internal combustion engine. Table 1 summarizes the maximum power for several engines.

TABLE 1
		Rated
ENGINE	Rated Power	Speed	Displacment	RPC	NMEP
Merc. 2.4 Litre	240 hp	7000 rpm	142 in3	1	96 psi
GM 5.7 Litre	210 hp	4400 rpm	350 in3	2	108 psi
DD 6V053TA*	350 hp	2800 rpm	305 in3	1	162 psi
Cummins 370B	370 hp	3000 rpm	379 in3	2	257 psi
*Detroit Diesel

A gas passageway 22, according to the present invention, is connected to the nozzle 14 at a region R₃ where the velocity of the water flow is being increased, yet prior to the water being expanded. This region R₃ is in a high-pressure region of the nozzle 14. The resulting thrust can be approximated by:

Thrust=(M+M_Exhaust)V_N−MV   (4)

where:

V_N=(2(P_Pump−P_Ocean)/ρ_Mixture)^1/2   (5)

This results in the exhaust 15 being mixed with water in the nozzle 14. Consequently, the density, ρ_Mixture, is decreased, the total mass flow rate, (M+M_Exhaust), is increased, and the thrust is increased. When the water propulsion apparatus 10 is used in combination with the engine (gas source) 12 which operates most efficiently at an increased NMEP, the result is a water propulsion apparatus having increased thrust, increased efficiency, and decreased noise levels.

The water propulsion apparatus 10 may be used in on personal watercraft (or “Jet Ski”) or high speed underwater vehicles (such as torpedoes) or high speed surface craft.

It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

Claims

1. An apparatus for water propulsion, said apparatus comprising:

a pump capable of pumping from a water source;

a nozzle in fluid communication with said pump, said nozzle including a first region capable of increasing a velocity of a water flow by a decreasing diameter of the nozzle and second region adjacent to and converging in diameter from said first region with said second region capable of producing a thrust based on the velocity of the water flow; and

a passageway communicating with an exhaust gas source and at a single point as an only point of passageway communication in said first region of said nozzle and prior to said second nozzle region such that the thrust is increasable by exhaust gas impacting the water flow.

2. The apparatus in accordance with claim 1 wherein said exhaust gas source is an engine.

3. (canceled)

4. (canceled)

5. A device for water propulsion, said device comprising:

a nozzle in fluid communication with a pump, said nozzle including a first region capable of being set to a first pressure and a second region adjacent to and converging in diameter from said first region, said second region capable of being set to a second pressure, wherein the first pressure is greater than the second pressure; and

a passageway communicating with a source of exhaust gas and at a single point as an only point of passageway communication within said first region of said nozzle, wherein said exhaust gas is combined with water in said first region to increase a thrust of the water propulsion based on a water flow within the nozzle.

6. A method of increasing a thrust of a water propulsion apparatus, said method comprising the steps of:

providing a pump;

producing an exhaust gas;

driving said pump;

providing a nozzle in fluid communication with said pump, said nozzle having a first region capable of increasing a velocity of flow of water and a second region adjacent to and converging in diameter from the first region, the second region capable of expanding the flow of water;

introducing the exhaust gas at a single point as an only point of the exhaust gas introduction in the first nozzle region while the velocity is being increased and prior to the second nozzle region wherein the water is being expanded; and

increasing a thrust by an increase in velocity resulting from the exhaust gas introduced at the point in the first nozzle.