HIGH EFFICIENCY ENGINE FOR ULTRA-HIGH ALTITUDE FLIGHT

• US 20130055984A1
• Filed: 11/19/2011
• Published: 03/07/2013
• Est. Priority Date: 09/07/2011
• Status: Active Grant

• Current Assignee: William Snell
• Original Assignee: William Snell
• Inventors: Snell, William
• Granted Patent: US 8,757,108 B2
• Time in Patent Office: Days
• US Class Current: 123/25.R
• CPC Class Codes: F02B 43/10 Engines or plants characterised by use of other specific gases, e.g. acetylene, oxyhydrogen
• CPC Class Codes: F02B 75/282 the pistons having equal strokes
• CPC Class Codes: Y02T 10/30 Use of alternative fuels, e.g. biofuels

Abstract

A high thermal efficiency reciprocating hydrogen-fueled engine for ultra-high altitude long endurance flight and its method of operation are described. The engine is based on an opposed piston barrel design where long cylinders are employed to accommodate extraordinarily large compression and expansion strokes where the corresponding ratios are over 50:1, taking advantage of the very low ambient air pressures and temperatures at 60,000 ft and higher to reduce the overall weight and strength requirements of the inventive engine that would be a factor for operation at lower altitudes. The engine is designed to obtain more than 70% indicated thermal efficiency when operated at ultra-high altitudes of 60,000 ft and greater. A combination of large compression ratios combustion temperature optimization and management, instantaneous and complete combustion at TDC, followed by a rapid and long expansion stroke using tailored control of piston movement provide the means to achieve such high efficiencies.

Claims

1. A method for operating an opposed-piston internal combustion engine cycle for enabling highly efficient stratospheric flight, comprising:

(i) Providing an activated internal combustion engine in operation having a plurality of cylinders, each cylinder enclosing a pair of first and second opposed pistons, wherein each piston translates back and forth along the long axis of the cylinder and wherein the combined motion of the piston pair is synchronized to allow the cyclical translation of the first piston to be in phase with the second piston whereby each piston reaches their respective top dead center and bottom center positions at substantially the same time, and whereby the volume of the cylinder is defined by the product of the distance between the top surfaces of the first and second pistons and the cross sectional area of the cylinder, the maximal volume V1 defined where the distance between the top surfaces of the first and second pistons is the largest in the engine cycle, the first and second pistons being at the bottom dead center position, and the minimal volume V2 defined where the distance between the top surfaces of the first and second pistons is the smallest in the engine cycle, the first and second pistons being at the top dead center position, the piston top surfaces being insulated;

(ii) Providing a gaseous working fluid having a temperature T1 below ambient stratospheric temperature and pressure P1 substantially at ambient stratospheric pressure, to an engine compartment housing the engine;

(iii) Opening one or more exhaust ports disposed in the wall of each cylinder substantially near the end of the expansion phase of the previous engine cycle wherein the volume of the cylinder is substantially near V0 and the pressure of the exhaust gases within the cylinder P4 is greater than the gaseous working fluid pressure P1 on the exterior of the cylinder wall, and whereby the exhaust gases expand and exit through said open exhaust ports, and wherein V0 is the volume at which the pistons are at the bottom dead center position;

(iv) Opening one or more intake ports disposed in the wall of each cylinder in succession to the opening of the one or more exhaust ports, whereby exhaust gases from the previous engine cycle are purged from the cylinder by means of a flow created by a pressure differential between the open intake and exhaust ports, and working fluid flows at pressure P1 into the cylinder through the open intake ports;

(v) Closing the open exhaust ports and returning the cylinder volume to V1 from V0 by engaging the pistons in a partial compression stroke, wherein the working fluid is maintained at a constant pressure by means of the open intake ports;

(vi) Closing the open intake ports and adiabatically compressing the working fluid in the cylinders, by moving the pistons towards top dead center from cylinder volume V1 to a final volume V2, wherein V2 is substantially less than V1 and the compression ratio V1/V2 is 50;

1 or greater, and wherein the volume V2 defines a combustion volume residing between the top surfaces of the pistons when both opposed pistons are at the top dead center position, whereby the value of V2 is such that the heat transfer surface area to volume ratio A/V2, wherein A is the total heat transfer surface area, comprising the intervening cylinder wall surface defined by the cylinder bore diameter and the distance between the insulated top surfaces of the opposed pistons, to volume V2, is at an optimal value in order to minimize combustion energy losses resulting from convective and conductive heat transfer to said wall surface;

(vii) Metering a fuel charge of liquid hydrogen into the combustion volume V2 wherein the fuel charge is measured to maintain an equivalence ratio phi between 0.4 and 1.0;

(viii) Metering a charge of water into the combustion volume V2 to provide a fluid means of partially absorbing the heat released from combustion of the fuel;

(ix) Combusting the fuel charge in the combustion volume V2 by spark ignition wherein the pistons are substantially stationary at the top dead center position for the duration of the combustion process and whereby spark formation and ensuing combustion is uniform in the cross section of V2; and

(x) Expanding the cylinder volume from V2 to V0 at a high initial velocity, wherein the pistons are propelled freely by the forces derived from the instantaneous pressure of the exhaust gases, from the top dead center position at V2 toward the bottom center position at V0 without mechanical constraint for an initial portion of the expansion stroke before mechanically engaging a coupling mechanism converting linear motion to rotational motion.

2. The method of claim 1, wherein the gaseous working fluid is selected from the group consisting of air, argon and xenon at stratospheric temperatures and pressures.

4. The method of claim 1, wherein the uniform spark formation is generated by a spark matrix disposed in the combustion volume V2 at a position equidistant from the top of each opposed piston when said pistons are at TDC.

5. The method of claim 1, wherein combustion volume V2 is maintained to be at least 35 in³ (575 cm³).

3. (canceled)