US2976860A - Gas fuel injection system - Google Patents

Description

March 28, 1961 R. J. BAYER 2,976,860

GAS FUEL INJECTION SYSTEM Filed July 51, 1959 5 Sheets-Sheet 1 IN VEN T OR.

ATTORNEY March 28, 1961 R. J. BAYER 2,976,860

GAS FUEL INJECTION SYSTEM Filed July 31, 1959 3 Sheets-Sheet 2 IN VEN TOR.

AT TORN E V March 28, 1961 R. J. BAYER 2,976,860

GAS FUEL INJECTION SYSTEM Filed July 31, 1959 3 Sheets-Sheet 3 soa- ZOMPRESSOR CYLINDER PRESSURE /F M) GAS WERE DELIVERED AS PREssuRE AIEcEssARv TO I 522255;: '5 AT POINT OF BEGINNING or 6A5 \l m e cy DELIVERY [8 AT 9, Ioo- CROSSOVER mIIvT ACTUAL COMPRESSOR I or COMPRESSOR CYLINDER PRESSURE CYLINDER PREssuRE g: AND GAS VALVE u,- OPEN/N6 PREssuRE u COMPRESSOR CYLINDER g INLET PRESSURE R 50 Q Q 78/? s. I.

30 ENG/NE CYLINDER PREssuRE a v I l I I l I 1 I l I Is 2 253 6 5678910 INVENgTOR.

COMPRESSOR CYUNDER %oI- DISPLACEMENT Io BY Foaf 5 7?; ZW Z A TORNEY GAS FUEL INJECTION SYSTEM Robert J. Bayer, Warren, Mich, assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed July 31, 1959, Ser. No. 830,813

Claims. (Cl. 123-46) This invention relates to internal combustion engines of the reciprocating piston type, and particularly to a gas fuel injection system therefor which requires no r tative driving gear.

It is frequently desirable to operate so-called free piston or crankshaftless enginess on natural gas fuel, which presents a problem in mechanical operation of the gas injection means by reason of the fact that all moving parts of the engine follow the same path on both inward and outward strokes of the power pistons. For example, a mechanically actuated gas fuel valve would be opened on both compression and expansion strokes unless some ratchet type drive was used.

It is the principal object of my invention to provide a gas fuel injection system for reciprocating piston type engines, wherein the need for any rotative driving gear, ratcheting device or hydraulic pressure lines are obviated, and which is relatively simple and efiicient in operation, is adapted for effecting any desired injection timing, and does not require excessive gas injection pressures to operate.

In general, the system, of my invention includes a piston type gas compressor supplied with gas fuel from a suitable source. The piston means in this compressor is so linked to a reciprocating power piston of the engine as to cause their compression strokes to occur simultaneously, with however the compression rate in the compressor being initially greater than that in the engine cylinder to supercharge the gas fuel to a value sufficiently high to force open a gas inlet valve against the compression pressure in the engine cylinder. After the gas inlet valve has opened, the relative rates of compression in the two cylinders is reversed, allowing the gas valve to re-close before ignition occurs. Preferably, the gas fuel is supplied at substantial line pressure, say 40 pounds per square inch gage (p.s.i.) to the engine driven compressor, and a compensating piston is provided which operates under such supply line (uh-supercharged) gas fuel pressure in opposition to engine gas valve opening movement. This reduces the size of the compressor required, and the compensating piston insures against the gas valve being opened prematurely during the engine operating cycle.

This and other objects and advantages of the invention will be more clearly understood from the following description of one preferred embodiment selected for purposes of illustration, having reference to the drawings, wherein:

Figure 1 is a longitudinal view of a portion of an opposed free piston engine, with parts broken away and in section and showing the mechanism for operating the gas fuel injection valve.

Figure 2 is an enlarged fragmentary sectional view similar to Figure 1 showing the gas fuel injection valve and the supercharging compressor in association therewith.

Figure 3 is a diagram showing the relative gas fuel and engine cylinder compression pressures during the period Patented Mar. 28, 1961 ice of gas fuel injection, as measured in terms of percent of displacement of the compressor piston means.

Referring now in detail to the drawings, and first to Figure 1, an engine cylinder is shown at 1 having opposed power pistons 2 and 3 reciprocable in opposite ends thereof, one of the pistons having a connecting rod 4 extending therefrom for driving a pump piston (not shown) in a larger work cylinder 5. A ring of engine combustion air intake and scavenging ports 6 are traversed by the power piston 2, and similarly a ring of exhaust ports 7 are traversed by the power piston 3. Between the opposing ends of the power pistons is a combustion chamber space 8, connected to which is a gas fuel injection valve designated generally by the numeral 9. Pivoted at 10 to the power piston connecting rod 4 is a link 11 whose opposite end is pivotally connected at 12 to the relatively long arm 13 of a two-arrn ink or bellcrank which is mounted for pivotal movement about a fixed axis 14- on a bracket 15 rigid with the cylinder 1. 16 is a compressor cylinder into which gas fuel is introduced via a passage 17 from a suitable pressure source (not shown) such as a natural gas supply line in the field at, say, 40 psi. gas pressure. Reciprocable within the compressor cylinder 16 is a piston means 18 in the form of a piston having a connecting link or rod 1% pivoted thereto at Ztl. The extending lower end of the connecting rod 19 is, in turn, pivotally connected at 21 to the relatively short arm 22 of the aforementioned bellcrank. Accordingly, during movement of the power piston 3 on its compression stroke (to the left as viewed in Figure l) the compressor piston means 18 is simultaneously driven upward on its compression stroke. The geometrical relation of the parts, including the relative lengths of the link 11, connecting rod 19 and bellcrank arms 13, 22, is such that after the engine cylinder ports 6 and 7 are closed a mechanical advantage initially exists in favor of the power piston 3 during its compression stroke, whereby movement of the compression piston means 18 occurs relatively faster. With continued movement of the power piston on its compression stroke, however, the mechanical advantage reverses in favor of the compressor piston means 18 for the remainder of such stroke, with the result that the rate of compression in the engine cylinder 1 substantially exceeds that in the compressor 16 by the time the power piston reaches the end of its compression stroke.

Referring to Figure 2., it will be seen that the gas fuel supply line passage 17 enters the compressor cylinder 16 via a check valve 23 which is openable inwardly of the compressor cylinder against a return spring 24. The gas injection valve 9 includes a valve body 25, compensating piston cylinder 26 and nozzle 27 in stacked superimposed relation within an outer shell 28 and clamped down against a seat 29 in the side wall of the engine cylinder 1 by studs 3%. The lower end of the nozzle 27 has openings 31 therethrough for passage of gas fuel into the combustion chamber 8 when a poppet valve 32 moves downwardly from its position shown to open a port 33 in the valve body 25. Thestem 34 of this poppet valve is slidably guided in the valve body and extends into the bore 36 of the compensating cylinder 26 wherein it carries a compensating piston 37. Between the compensating piston 37 and the valve body 25 is resilient means in the form of a compression spring 38 which normally holds the poppet valve closed. The upper end of the bore 36 is vented by an opening 39, while its lower end is closed by the upper end of the valve body 25. A gas fuel passage 40 connects the compressor cylinder 16 with the upper side of the poppet valve 32, and a similar gas fuel passage 41 connects the compensating cylinder bore 36 below the piston 37 with the gas fuel supply line 17 at a pointanterior therein of the check valve 23.

The operation of the gas fuel injection system can best be described with reference to specific dimensions, spring force and gas pressures of a representative engine installation. Using, therefore:

Diameter of compressor piston 1'8"... 2.25 in. Stroke of compressor piston 18 1.93 in. Clearance volume of compressor cylinder 18 (including volume in passages 40) 1.6 cu.in. Compressor pressure to overcome poppet valve spring 38 l p.s.i. Area of compensating piston 37 11.7 area of poppet valve 32.

for the gas used is 1.3, and that the equivalent :2 for air is 1.38. Using log-log graph paper having absolute pressure on the vertical axis and compressor cylinder displacement on the horizontal axis, a plot is made of compressor cylinder pressure. If it is assumed that no gas leaves the compressor cylinder, this plot appears as a straight line of slope 1.3. In this example, the compressor cylinder inlet pressure from the supply source (via line 17 in Figures 1 and 2) is taken as 55 p.s.i. absolute, or 40 p.s.i. gage. The engine cylinder pressure is also plotted, but it does not appear as a straight line because the change in power cylinder displacement is not linear with change in compressor cylinder displacement. From the formula: engine cylinder pressure-kcompressor cylinder inlet pressure 1.7+l0 p.s.i.:gas valve opening pressure it will be seen that the compressor cylinder pressure must be equal to engine cylinder pressure plus 78 p.s.i. to deliver gas. A plot of gas valve opening pressure is then made, which is simply engine cylinder pressure plus 78 p.s.i. As will be seen, the compressor cylinder pressure line (11:1.3) crosses the valve opening pressure line at approximately 96 p.s.i. absolute and 65% of the compressor cylinder displacement. Gas delivery begins at this intersection. As the compressor piston continues to move, gas is delivered to the engine cylinder and the compressor cylinder pressure follows the'gas valve opening pressure line (neglecting pressure drop in the connecting lines). Such gas delivery to the engine cylinder continues until the slope of the gas valve opening pressure line exceeds 1.3. At this point the rate of pressure rise in the compressor cylinder becomes equal to and then less than the rate of pressure rise of the gas valve opening pressure. The gas valve 32 then closes, occurring as shown in Figure 3 at 152 p.s.i. absolute and 22.5% of the compressor cylinder displacement. The amount of gas delivered to the engine cylinder is calculated as follows:

Weight of gas delivered per cycle:(weigl1t of gas in gas cylinder at beginning of compression)-(weight of gas in gas cylinder when gas valve closes) Weight of gas delivered per cycle:

P :gas inlet pressure=55 p.s.i. absolute V :O% of compressor cylinder displacement:

[3.14(2.25 )(1.93)/4]+1.6 T T =gas inlet temperature=150 F.

4 P =gas pressure when valve c1oses:152 p.s.i. absolute V :gas volume when valve closes:

([3.14(2.25 )(1.93)/4] +1.6) (.225) 1728 T =gas temperature when valve closes= Weight of gas delivered per cycle:.000725-.000357 Weight of gas delivered per cycle=.000368 pound The gas valve 32 also opens after the power cylinder ports 6 and 7 are closed, and it always closes before combustion begins. Since the compressor piston travels only a very short distance after the gas valve 32 is closed, the peak pressures in the system are kept low. In the specific system described above they do not exceed 300 p.s.i., which keeps the load on the driving mechanism from being excessive. The beginning of injection can be varied by changing the force of the poppet valve return spring 38 and/or the area of the compensating piston 37. Increasing the force of spring 38 retards gas delivery, the eifect being much more pronounced at low gas inlet pressures (from supply line 17) than at high gas inlet pressures. Increasing the area of the compensating piston 37 also retards the beginning of injection, but its elfect is more noticeable at high gas supply line pressures. Reducing the clearance volume in the compressor cylinder 16 and passage 40 increases the volumetric efiiciency of the system. Losses due to any lag in the opening of the gas valve are slight and are minimized by making this valve and the compensating piston 37 as light as possible. A slight delay in the closing of the gas valve 32 will result in a somewhat larger gas delivery, since gas valve opening pressure exceeds engine cylinder pressure for a short period after the theoretical closing time of the gas valve.

While only a single preferred embodiment of the invention has been disclosed, it is appreciated that numerous minor changes in the construction and arrangement of the parts may be made without departing from the spirit and scope of the invention as defined in the following claims.

I claim:

1. In a gas fuel injection reciprocating piston engine, an engine cylinder including a combustion chamber, a power piston reciprocable in the cylinder, means for introducing combustion air into and exhausting combustion products from the combustion chamber, a gas fuel injection port communicating with the combustion chamber, a source of gas fuel under pressure, gas fuel injection means between said source and said port including a compressor cylinder supplied by said source and a gas fuel passage connecting said compressor cylinder to said port, a valve controlling said port, resilient means biasing the valve closed, piston means operable in the compressor cylinder for supercharging the gas fuel pressure in the passage, said valve being operable inwardly of the combustion chamber and against the biasing force of said resilient means in response to compressor supercharged gas fuel pressure in the passage, and means drivingly connecting said compressor piston means to said power piston for actuating said piston means on its compression stroke during the compression stroke of the power piston, said connecting means providing a mechanical advantage in favor of the power piston during a first portion of its compression stroke, whereby the rate of compression in the compressor cylinder exceeds that in the combustion chamber by an amount suflicient to effect opening of the 5 valve in advance of the power piston completing its stroke.

2. The invention of claim 1, wherein said connecting means provides a mechanical advantage in favor of the compressor piston means during the remainder of said power piston stroke, whereby excessive supercharging of the gas fuel pressure is avoided.

3. The invention of claim 1, together with a compensating piston movable with the valve, and means subjecting said compensating piston with gas fuel pressure from said source to oppose its movement in the valve opening direction.

4. The invention of claim 1, wherein said connecting means includes a first link pivotable about a fixed axis, a second link having pivotal connections with said compressor piston means and said first link, and a third link having pivotal connections with said power piston and said first link, the relative distances between said pivotal connections and said axis being such that the velocity of said compressor piston means increases relative to that of the power piston during a portion of the power piston compression stroke.

5. In a gas fuel injection free piston engine, an engine cylinder, a pair of opposing power pistons reciprocable in opposite ends of the cylinder and defining a combustion chamber between them intermediate the ends of the cylinder, scavenging inlet air and exhaust ports in the respective ends of the cylinder traversed by said power pistons, a gas fuel injection port communicating with said combustion chamber, a source of gas fuel under pressure,

gas fuel injection means between said source and said port including a compressor cylinder, a first gas fuel passage connecting said compressor cylinder to said source, a check valve in said passage openable toward said compressor cylinder, a second gas fuel passage connecting said compressor cylinder to said port, a poppet valve controlling said port and openable toward said combustion chamber, resilient means biasing the poppet valve closed, a compensating piston movable with said poppet valve, a cylinder slidably supporting said compensating piston and closed at its end toward which the compensating piston moves during valve opening, a third gas fuel passage connecting said last named cylinder to said first passage anteriorly of the check valve, a connecting rod pivotally connected to said compressor piston and having an end extending therefrom, a link pivotally connected to one of the power pistons and having an and extending therefrom, and a bellcrank having a pivotal connection about an axis fixed relative the engine cylinder and having relatively short and long arms extending from said axis and pivotally connected to said connecting rod and link ends, respectively.

References Cited in the file of this patent UNITED STATES PATENTS

Images