Patent Application
20150098842
This invention relates to an improved apparatus marine propulsion system, under the classification of marine ramjet drive.
All known propulsion systems, land, air, marine or space, can be classified into two categories, impulse and traction. Propellers belong to the traction system, and utilize external (earth bound) references to provide propulsive effort. Whereas, most but not all marine jet drives belong to impulse system, and work with internal references.
Prior propulsion systems powered by a piston engine or electric motor consists of the screw propeller and “jet drives” for the marine industry. To date, the screw propeller represents the backbone of the non-wheel traction based propulsion systems.
In spite of its popularity and simplicity, the screw propeller being a “traction based device,” the magnitude of thrust is by design inversely proportional to the speed of the vessel. This is because, the output from the engine in foot-pounds per second is limited to the HP installed. Therefore the product of two variables, feet and pounds being fixed to the HP available, we can only increase pounds of thrust at the expense of speed or vice versa. In other words, faster the vessel travels lower the magnitude of thrust.
Whereas jet drive systems, ones which qualify under the “impulse system” are based on “internal references,” therefore have less dependency on the speed of vessel being propelled. This makes impulse based drives particularly suitable for high speed applications.
In all industries, any significant improvement in power demand is of great consequence since high powered piston aircraft, ferries, luxury motor yachts, and navy vessels for instance require a lot of power for propulsion.
Presently all jet drive systems in the marine industry consist of an intake, typically at the bottom of the vessel with a duct to direct the fluid into the impeller where mechanical energy is added to accelerate the fluid. The impeller designs vary from radial flow to axial flow, and most are mixed, transitioning between the two. The accelerated fluid is then directed through a converging section fitted with internal stator vanes directing the flow to the discharge nozzle. The net result is the impulse thrust, solely based on the accelerated fluid.
The magnitude of the net thrust is the outcome of selected design parameters, i.e., the mass flow rate and the degree to which the fluid is accelerated. These two design parameters along with system efficiency determine both HP demand as well as net thrust.
Three existing patents utilize a variable intake concept to improve the efficiency of the system. U.S. Pat. No. 0,281,375 and World Patent 052721 with same content by Jeff Jordan discusses variation in mass flow rates to improve the efficiency along with a variable pitch propeller. U.S. Pat. No. 4,373,919 by Maynard Strangeland for a flow splitter in the intake duct to minimize overall angle between two surfaces to improve the efficiency of the diffuser by avoiding flow separation and vortex. None of the above patents have the ability to benefit from an internally pressurized housing as a secondary thrust Component much like a ramjet. In all above patents the HP demand would vary approximately exponentially with speed since there is no way of getting around the equation, thrust=mass flow rate x change in velocity from intake to exit. Reduction in flow rate at high speed would require even higher exit velocities requiring exponentially higher power draw. Jeff Jordan's patent also utilizes a converging nozzle, item 70, which defeats the purpose of internal pressurization as the converging discharge nozzle would create significant thrust in the opposite direction. Therefore in the above patents the variable intake feature is used for flow control and not for pressurization of the housing. In any case the use of a propeller, with variable pitch or not, downstream from the diffuser would depressurize the diffuser defeating the potential for secondary thrust component.
It is the object of this invention to improve the magnitude of thrust delivered by both marine jet drive and propeller systems.
This invention provides the unique ability to create a secondary thrust component, like a ramjet from the pressurized diffuser by utilizing three key features collectively as outlined below. Without the second thrust component replacing the loss of mass flow rate would only drive the power requirement even higher.
The first feature is the variable intake area which has the ability to provide high volume intake for low speed operations, while reduced area for medium to high speed operation. The reduction of intake area allows the incoming fluid to decelerate and pressurize the diffuser intake duct, thus providing a secondary thrust component adding to the overall propulsive effort.
The second feature is the result of the dynamics associated with an impeller working in a slower stream of fluid, thus requiring significantly less horsepower to develop the same propulsive effort. In this case, the angular velocity of the fluid is zero before it engages with the impeller.
The third feature comes from spinning the fluid inside an expanding chamber. This is perhaps the most significant feature in making the diffuser work to pressurize. This action deflects all of the deceleration forces to the expanding housing and creating backpressure without a conventional nozzle. In high speeds, the total propulsive effort from the three features can be easily double that of any existing propeller or marine jet drive system with the same input horsepower.
In the attached drawings,
This invention provides significant improvement over the existing impulse or jet drive systems by manipulating two equations; thrust, F=mass flow×(exit velocity−inlet velocity), and HP demand=mass flow×(exit velocity squared−inlet velocity squared)/(foot-pounds per HP×efficiency of the system).
The thrust gained from the diverging inlet conduit is calculated from Bernoulli's equation, Pa−Pb=ΔP=(mass flow/2×g)×(outlet velocity squared−inlet velocity squared). And, added thrust from diffuser intake, F1=(a2−a1)×(Pa−Pb)/2.
Typically, as in the prior art with jet drives, any positive forces in the impeller housing are cancelled by the converging discharge nozzle producing zero thrust leaving only F2=mass flow×(exit velocity−inlet velocity) for thrust. In the present art also, if we leave everything the same but change the impeller to a conventional screw type would necessitate a converging section which would nullify the thrust gained in the inlet section.
By spinning the fluid inside the impeller housing, all of the dynamic forces acting on the internal surfaces are directed toward the outer housing, relieving the hub of all stagnation forces. This is achieved by maintaining the centrifugal pressure higher than the stagnation pressure.
The angular acceleration when converted to axial provides a very efficient mechanical means of providing the second thrust component. The total thrust is then, total thrust, Ft=F1+F2. However, since the impeller is working in a lower velocity fluid than the forward velocity of the vessel, the HP demand is reduced significantly for the same magnitude of thrust.
The impeller housing profile is designed to provide constant acceleration to convert the radial pressure into axial flow. The impeller having zero pitch, only provides the centrifugal force. The resulting angular efflux is directed into the curved stators to convert all angular velocity into axial flow.
For the marine industry, a standard rudder at the exit nozzle provides steering capability. And, reverse thruster nozzles (not shown) can be added to provide the reverse maneuvering.
Related Patents reviewed:
U.S. Pat. No. 5,876,258 U.S. Pat. No. 8,403,715
U.S. Pat. No. 5,720,635 U.S. Pat. No. 6,722,934
U.S. Pat. No. 5,577,941 U.S. Pat. No. 6,364,725
U.S. Pat. No. 5,509,832 U.S. Pat. No. 6,358,107
U.S. Pat. No. 5,421,753 U.S. Pat. No. 6,200,176
U.S. Pat. No. 3,994,254 U.S. Pat. No. 6,045,418
U.S. Pat. No. 3,945,201 U.S. Pat. No. 0,281,375
World Patent 052721 U.S. Pat. No. 4,373,919
