GB2413361A

GB2413361A - Fixed-displacement i.c. engine with expansion ratio greater than compression ratio

Info

Publication number: GB2413361A
Application number: GB0408746A
Authority: GB
Inventors: Leslie Maidment
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-04-20
Filing date: 2004-04-20
Publication date: 2005-10-26
Also published as: GB0408746D0

Abstract

A fixed-displacement i.c. engine has compression cylinders 2 which compress air into separate, closely connected, valved combustion chambers 3 within the cylinder head 4 from which the gases are released after combustion into larger expansion cylinders 5 located adjacent the compression cylinders 2. A single compression cylinder may be arranged between two expansion cylinders (fig.4). The combustion chamber valves 8, 9 may be outwardly-opening (figs.2,3). The valves 8-11 and the combustion chamber 3 may be arranged in a rotor (11, fig.5) or may be sleeve valves (fig.6). With this arrangement, the air charge is not heated by combustion gases, or surfaces heated by them, so the expansion ratio is much greater than the compression ratio and there is more time available for combustion at constant volume. The volumetric, combustion and thermal efficiencies of the engine are consequently increased.

Description

1 2413361

A MORE EFFICIENT AND POWERFUL FIXED-DISPLACEMENT

INTERNAL COMBUSTION ENGINE

This invention concerns a fixed-displacement internal combustion engine, having greater efficiencies and power, principally by virtue of an expansion ratio which is significantly greater than its compression ratio.

The theoretical heat efficiency of the internal combustion engine depends upon the degree to which the air is compressed before the combustion starts and the degree to which it is expanded after the combustion is completed. For the present fixed- displacement engine, the compression ratio and the expansion ratio are equal and, when combustion is completed before the start of the expansion stroke, the degrees of compression and expansion are equal, and the air- cycle concerned is known as the Constant Volume cycle. With this cycle, for a given cylinder design pressure, the higher the value of the compression ratio (rc), the lower the allowable heat-input and the power obtainable. A high thermal efficiency and high power are, therefore, not obtainable, at reasonable cost. Also, if the fuel is volatile (e.g. petrol) a high expansion ratio (re) and high efficiency are precluded, because of the low compression ratio necessary to prevent pre-ignition of the fuel.

A non-volatile fuel (e.g. diesel oil) necessitates a high rc for autoignition of the fuel and, therefore, for a given cylinder design pressure, a high heat-input and power can be employed, only if the input is made mainly, or completely, during the expansion stroke. However, the expansion of the gas obtained thereby is less than the compression of it - and the heat efficiency is, therefore, reduced accordingly. The air cycle concerned is either Constant Pressure, or Composite (i.e. a mixture of Constant Volume and Constant Pressure).

With the maximum possible heat-input rate and a cylinder design pressure of 1000 p.s.i., the Constant Volume petrol engine gives an efficiency of about 54%; the Constant Pressure, Diesel engine an efficiency of about 62% and the Composite petrol engine an efficiency of about 59% - for rc values of 6.7, 20 and 10, respectively.

Also with the present engine, compression, combustion and expansion within the same cylinder results in a reduction of the volumetric and combustion efficiencies because of heating of the air intake by the hot cylinder and by residual exhaust gas, and because the time available for combustion is so little. Cylinder hot-spots can also reduce the value of rc usable with a given volatile fuel, because of the need to avoid a risk of 'trot-spot pre-ignition'.

The purpose of this invention is the increase of the engine's efficiencies and power, without increase of its design pressure and cost.

According to the invention, there is provided an engine having an re much greater than its rc' because some cylinders provide for an induction/compression process, while others provide for an expansion/discharge process, the total volume of which exceeds that of the induction/compression cylinders; and because combustion takes place within separate combustion chambers, closely coupled to them, via fast acting inlet and outlet valves which cause only an acceptable degree of throttling of the expansion of the combustion gas, during its transfer to the expansion/discharge cylinders; wherein the ascent of the piston of the expansion cylinder lags behind that of the piston of the compression cylinder, sufficiently to allow a greater time for heat input at Constant Volume, and for subsequent equalization of the combustion chamber and expansion cylinder pressure, before start of the descent of its piston; wherein the combustion chambers are either within the cylinder-head, immediately above their complimentary cylinders and have cam-operated, reciprocating inlet and outlet valves, or are located at the top of the cylinder-block between their complimentary cylinders and have their inlet and outlet valves provided within the cylinder-head (immediately above their complimentary cylinders) and have rotating inlet and outlet valves provided by means of the rotor; whereby, as a result of the stated provisions, the theoretical heat efficiencies obtainable for the Constant Volume (petrol) Constant Pressure (Diesel) and Composite (petrol) engines are increased to about 82%, 74% and 75%, respectively, because the theoretical heat efficiency increases with increasing values of rc/rc (as shown by the expressions given in the Appendix) Also, the heat energy and frictional energy losses are reduced and the volumetric and combustion efficiencies are increased.

Six embodiments of the invention will now be described (for example purpose only) with reference to the following figures in which: Figure 1. gives a schematic arrangement of the first embodiment of the invention.

Figures 2. and 3. gives details of the valves required for the first embodiment.

Figure 4 gives a schematic arrangement of the second embodiment.

Figure 5 gives a schematic arrangement of the third embodiment.

Figure 6 gives a schematic arrangement of the fourth embodiment.

Referring to Fig. 1. for the first embodiment, the engine, in its simplest possible form, consists of a compression cylinder 2; a separate combustion chamber 3 located above that cylinder, as closely as possible to it within the cylinder-head 4; an expansion cylinder 5 adjacent to the cylinder 2; connections 6 and 7, central to the length of the combustion chamber 3, for provision of fuel ignition and/or fuel injection; levered, reciprocating, partially pressure-balanced valves 8 and 9 (shown in Figs. 2 and 3) for control of the flow through the combustion chamber 3; similar valves 10 and 11 for control of flow into and out of the engine: and the camshaft, 12 located upon the cylinder-head, for driving the said valves.

The ascent of the piston 13 precedes that of the piston, 14, so that there is an adequate time for a reasonable period of Combustion at Constant Volume and for sufficient combustion gas to leave the combustion chamber 3 and cause equalization of pressure within the cylinder 2, simultaneously with the start of the descent of the piston 14.

The exhaust valve 11 closes and the combustion chamber outlet valve opens no sooner in the ascent of the piston 14 to its T.D.C. than is essential for the stated equalization of pressure; and, to that end, the opening and closing time of the valves concerned is preferably less than 10% of the piston's stroke-time; and the valve's port-size is as large as can be conveniently accommodated - preferably not less than 10% of the cylinders cross-sectional area. For a petrol engine having a compression ratio of 5/1 and an expansion ratio of 10/1, the diameter of the expansion cylinder 5 is 1.412 x diameter of the compression cylinder 2.

The piston's stroke-length is the same for both cylinders and its T.D.C. clearance is about 0.5% of the stroke-length, in order to adequately limit the energy lost during transfer of the compressed air from the compression cylinder to the combustion chamber, and the amount of non- productive expansion of combustion gas into the clearance volume of the expansion cylinder S. Also, the heat rejected by the exhaust stroke is reduced by a factor of I - l/re because the energy in the expanded gas left within the combustion chamber contributes to the heating of the combustion chamber during the subsequent combustion.

Referring to Figs 2 and 3, it can be seen that the valves 8 and 9 are located as closely as possible to the cylinder wall common to cylinders 2 and 5. This allows minimization of the combustion chamber's length and maximization of its cross- section, compatible with the provision of the required combustion volume. It can also be seen that the force required to open the outlet valve 9, against the combustion pressure trying to close it, is reduced because the diameter of the valve's stem is approximately equal to that of the valve-port. The valve-seat 17 and the valve-stem sleeve 18 are provided to give long-life, low-leakage valves, operated by the levers 19, the springs 20 and the camshaft 12.

Referring to Fig 5 for the second embodiment, the engine is similar to that of the first embodiment, except that the valves 8, 9, 10 and I I and the combustion chamber 3 are provided within an engine-driven rotor 11, located within the cylinder-head 4, as closely as possible to the top of the cylinder-block 15. The rotor 11 runs in a sleeve (not shown); and both rotor and sleeve are hardened and ground to give exceptionally small clearances, negligible leakage and a long-life, enhanced by engine oil lubrication.

Referring to Fig 6 for the third embodiment, the engine is as described for the first embodiment (Fig l) except that the valves 8, 9, 10 and l I are provided by means of cylinder sleeves 20 and 2], the downward movement of which causes opening of the exhaust port 22 and the air inlet valve 23, and the upward movement of which causes closure of the air inlet port 24 and the combustion chamber outlet port 25. This arrangement provides the lowest resistance to the transfer of gas into and out of the combustion chamber and, therefore, the highest thermal efficiency. It also provides the best protection against combustion, shock-wave damage of the engine.

Referring to Fig 4 for the fourth embodiment, the engine is the same as stated for the first embodiment (Fig l), except that the engine block 15 contains three cylinders and two combustion chambers 3. The compression cylinder is the central cylinder 2 which has a diameter equal to that of the expansion cylinder located on either side of it. This gives a re/rc ratio (is) equal to 2, and for a value equal to 3, the diameter of the expansion cylinder equals 1.224 times that of the compression cylinder.

For the fifth embodiment, the engine is the same as that described t'or the fourth embodiment (Fig 4), except that the combustion chamber and valve provision is the same as that stated for the second embodiment (Fig 5).

For the sixth embodiment, the engine is the same as that described for the fourth embodiment (Fig 4), except that the combustion chamber and valve provision is the same as that stated for the third embodiment (Fig 6).

Claims

]. A fixed- displacement internal combustion engine having an expansion ratio re much greater than its compression ratio, rc, principally because the induction/compression process is conducted in some cylinders and the expansion/exhaust process in an equal number of the same diameter; and because the combustion is mainly, or entirely, conducted within separate, and closely coupled valved combustion chambers, from which the gas is discharged into the expansion cylinders with an acceptably low degree of throttling and a small concomitant, expansion-energy loss; whereby the theoretical thermal efficiency increases with increasing values of the ratios re/rc (as shown by the expressions given in the Appendix) and is consequently much greater than that available with the present engine of comparable capacity and speed, for Constant Volume, Constant Pressure and Compost air cycles.
2. An engine as in Claim 1, comprised partly of compression and expansion cylinders; combustion chambers located close to the cylinders, within the cylinder-block between a compression cylinder and an expansion cylinder, as closely as possible to the top of the cylinders; short, 'maximumpossible-area' flow-passages connecting the cylinder to the combustion chambers; a flow path through the combustion chamber which is as short as possible and of a cross-section as large as possible for the combustion volume required; when the combustion chambers are within the cylinder-head, reciprocating pressure- balanced, camshaft and lever operated inlet and outlet valves for the combustion chamber control; when the combustion chambers are located within the cylinder-block between the cylinder's, inlet and outlet valves provided by means of reciprocating cylinder sleeves; a rotor within the cylinder-head which gives an alternative means of provision for the combustion chambers and rotary valves for their control; a camshaft upon the cylinder head for control of the lever-operated valves, or the cylinder-sleeves; and connections through the cylinder-head, centrally to the top of the combustion chambers, for spark-ignition and/or fuel injection; wherein the T.D.C clearance volume of the pistons, is, preferably, not greater than 0.5% of the piston's displacement volume; wherein the ascent of the compression pistons precedes that of the expansion pistons, sufficiently to provide for a reasonable time for combustion at Constant Volume and for a sufficient discharge of combustion gas into the expansion cylinder to equalise the combustion chamber and expansion cylinder pressures, as the expansion cylinder piston reaches its T.D.C; wherein to achieve the said equalization of pressures, the exhaust valve is closed and the combustion chamber outlet valve opened, as late as acceptable during the ascent of the expansion cylinder's piston, and the said valves close and open in a time, preferably not greater than 10% of the piston's stroke-time; wherein the combustion chamber's inlet valve does not open during the compression stroke, until the compression pressure is equal to the exhaust pressure retained within the combustion chamber, from the prior expansion stroke.
3. An engine as in Claims I and 2, except that there are twice as many expansion cylinders as compression cylinders.
4. An engine as in Claims 1, 2 and 3 which has a higher actual thermal efficiency than that of the present engine, not only because of a higher theoretical thermal efficiency but also because of reduced water-jacket and radiation heat losses and reduced driving-friction losses which arise from the smaller surface area/volume ratio of the combustion vessel, from the absence of combustion gas temperature from,/i or I/: of the cylinders, and from exclusion of the worst of the combustions pressure and shock effects from the piston and drives which, consequently, can be lightened.
5. An engine as in Claims 1, 2 and 3 which has higher volumetric and combustion efficiencies and lower suspectability to 'hot-spot preignition' because combustion and the resulting gas are eliminated from the compression cylinder; because there is more time for combustion at Constant Volume, and because the adverse effect of the combustion at Constant Volume is compensated for by the provision of a larger expansion ratio.

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