Swirl-Chamber Diesel Engine With Swirl Chamber Having Depression for Collecting Fuel Droplets

The present invention relates to swirl-chamber Diesel engines.

Swirl-chamber Diesel engines comprise a cylinder block, a piston reciprocally disposed in a cylinder of the cylinder block, a cylinder head secured to the cylinder block and closing the cylinder, a main combustion chamber formed in the cylinder between the piston and the cylinder head, a generally spherical swirl chamber formed in the cylinder head and a communication passage formed in the cylinder head to establish communication between the main and auxiliary combustion chambers. The communicating passage connects tangentially into the swirl chamber so that during the compression stroke of the piston part of air charge in the main combustion chamber flows into the swirl chamber along a line tangent to the wall thereof to generate swirl therein. A fuel injection nozzle is mounted to the cylinder head and opens into the swirl chamber. Within the swirl chamber a shoulder is formed around the port of the passage at which the passage opens into the swirl chamber and located on the opposite side to the side along which air flows into the swirl chamber from the communicating passage during the compression stroke of the piston. The injection nozzle points toward the shoulder so as to direct jet of fuel toward and along the swirl of air in the swirl chamber such that the jet of fuel will not enter directly into the main chamber through the communicating passage. A heater plug or glow plug extends into the swirl chamber to produce heat close to the jet of fuel to give a starting aid. The piston is formed at its crown with a depression of a spherical design. This depression, when the piston is on its top dead center, forms part of the complete combustion chamber. It consists of cup-shaped cavities communicating at their junctions with the swirl chamber. By dividing the subsequent combustion gases flow from the passage into two streams flowing around the cup-shaped cavities some degree of air swirl during combustion is generated outside the swirl chamber; this encourages the feeding of fresh air to the emerging fuel.

In regard to operation of the Diesel engine constructed as above, during the compression stroke of the piston, the air charge in the main combustion chamber is compressed so that part thereof flows into the swirl chamber through the communicating passage thereby to generate swirl therein so as to be compressed to produce a heat zone at the center of the swirl. The jet of fuel from the fuel injector or injection nozzle is directed into the swirl to be ignited by the heat generated by the swirl. The subsequent combustion gases flow into the main combustion chamber from the communicating passage to effect diffusion burning.

In operation, when the engine, as constructed above, runs at low engine speed, such as, when the engine is idling, the swirl of air within the swirl chamber is weak and not strong enough so that the fuel injected from the nozzle will not mix well with the air. The fuel droplets, therefore, tend to adhere to the swirl chamber wall, flowing along the wall of the passage into the main combustion chamber, thus likely to result in ignition within the main combustion chamber and in knockings.

It is therefore an object of the present invention to improve a swirl-chamber Diesel engine by preventing unfavorable flow of fuel, in liquid form, toward a main combustion chamber from a communicating passage.

According to the present invention, a swirl chamber has formed therein a depression which will collect fuel droplets within the swirl chamber to prevent them from entering into a communicating passage. The depression is disposed adjacent to and communicates with a communicating passage via a rounded lip. This arrangement will make it easy for combustion gases flow to draw the fuel from the depression thereinto.

In the accompanying drawings

FIG. 1 is a partial sectional view of a conventional swirl-chamber Diesel engine;

FIG. 2 is a cross sectional view of the engine of FIG. 1 showing the shape of the combustion chamber cavity;

FIG. 3 is a partial sectional view similar to FIG. 1 showing a first preferred embodiment of a Diesl engine according to the present invention;

FIG. 4 is a similar view to FIG. 3 showing a second preferred embodiment according to the present invention; and

FIG. 5 is a similar view to FIG. 3 showing a third preferred embodiment according to the present invention.

Before entering into the description of the preferred embodiments of the present invention, the conventional swirl-chamber Diesel engine will be explained in connection with FIGS. 1 and 2 so as to make clear the feature of the invention over the prior art.

A swirl chamber Diesel engine shown in these Figures comprises a cylinder block 1, a piston 2 reciprocally movable in a cylinder formed in the cylinder block 1 and a cylinder head 4 secured to the cylinder block 1 to close the cylinder so that a main combustion chamber 3 is formed in the cylinder between the crown of the piston 2 and the cylinder head 4. The cylinder head has formed therein a swirl chamber 5 communicating with the main combustion chamber 3 through a communicating passage 6 also formed through the cylinder head 4. The passage 6 is so shaped and inclined as to permit, during the compression stroke of the piston 2, part of air charge within the main combustion chamber 3 to enter into the swirl chamber 5 along a line tangent to the swirl chamber wall thereby to generate swirl in the swirl chamber 5. A fuel injector or injection nozzle 7 is mounted to the cylinder head 4 with its spout communicating with the swirl chamber 5. The fuel injection nozzle 7 points to the swirl chamber 5 wall disposed adjacent a shoulder 8 and is inclined such that jet of fuel injected from the fuel injection nozzle 7 may be directed along the swirl of air within the swirl chamber 5 and may not enter directly into the main combustion chamber 3. A heater plug or glow plug 9 extends into the swirl chamber 5 to produce heat close to the fuel to give starting aid. The piston 2 is formed at its crown with a depression 10 of a spherical design. This depression 10, when the piston 2 is on its top dead center, forms part of the complete combustion chamber. It consists of two cup-shaped cavities communicating at their junctions with the swirl chamber 5. By dividing the subsequent combustion gases flow from the communicating passage 6 into two streams flowing around the cup-shaped cavities, some degree of air swirl during combustion is generated outside of the swirl chamber 5; this encourages the feeding of fresh air to the emerging fuel.

In regard to operation of the conventional Diesel engine, during the compression stroke of the piston 2, the air charge within the main combustion chamber 3 is compressed so that part thereof flows into the swirl chamber 5 through the communicating passage 6 thereby to generate swirl therein so as to be compressed to produce a heat zone at the center of the swirl. The jet of fuel injected from the fuel nozzle 7 is directed into the swirl to be ignited by the heat generated by the swirl. The subsequent combustion gases flow into the main combustion chamber 3 from the communicating passage 6 into the main combustion chamber 3 to effect diffusion burning. The problem to be solved is that, when the engine runs at low speeds, such as at a idling, the swirl of air charge within the swirl chamber 5 is weak so that the fuel droplets having failed to be carried by the swirling air are likely to adhere to the wall adjacent the shoulder 8, flowing along, in liquid form, along the wall of the passage 6 toward the main combustion chamber 3, resulting in ignition within the main combustion chamber 3 and in knockings.

The preferred embodiments according to the present invention will be described hereinafter in connection with FIGS. 3 through 5 in which the same reference numeral as used in FIGS. 1 and 2 are used to designate similar parts to those shown in FIGS. 1 and 2.

As shown in FIG. 3, a depression 11 is formed at that area around adjacent port of a communicating passage 6 and adjacent a shoulder 8 on which the fuel droplets which failed to be carried by the swirling air will impinge when the engine runs at low engine speeds, such as, when the engine is idling. In this embodiment, the depression 11 is located on a straight line (X) extending from a fuel injection nozzle 7. It consists of a cavity plunging or depressed into the body of the cylinder head from the wall which curves generally along the paths along which the air within the swirl chamber will move.

At that part of the port of the passage 6 which is disposed adjacent to and connects into the depression 11, the port of the passage 6 is rounded as at 6a to provide a rounded lip. The purpose of the provision of the rounded lip 6a is to make easy the drawn-out of the collected fuel droplets into the stream of burning combustion gases as the combustion gases flow into the main combustion chamber 3 from the swirl chamber 5.

The location of a glow plug 9 in this embodiment is different from the glow plug location of the conventional engine as shown in FIGS. 1 and 2. As shown in FIG. 3, the electrode of the glow plug 9 is located adjacent the upper wall portion of the swirl chamber 5 so as not to decrease the swirl rate of air within the swirl chamber 5. Preferably, the electrode of the glow plug may be located adjacent that side wall of the swirl chamber on which the depression 11 is located with its tip approaching the depression 11. With this glow plug arrangement the collected fuel droplets in the depression 11 may be ignited by the heat of the glow plug 9 upon starting the engine and the ignition delay may be thus shortened as compared to the case in which the fuel droplets entrained by the swirling air is ignited. The results in a reduction in combustion noise.

When the engine runs at low engine speeds, such as, when the engine is idling, the fuel droplets that have failed to mix with the swirling air in the swirl chamber 5 may be collected in the depression 11 because the swirling air motion under this engine operating condition is not so strong enough to carry all fuel droplets. Since the upstanding depression wall section, which connects smoothly into the swirl chamber wall, is depressed away from the paths along which swirling air will flow the collected fuel droplets will not be drawn out of the depression by the swirling stream of air. Thus, under engine operation at low engine speeds, such as, at idling, fuel droplets are prevented from dropping along the passage wall into the main combustion chamber 3 and knocking at idling, which often encountered in the conventional engine shown in FIGS. 1 and 2, is prevented in the engine embodying the present invention.

After the subsequent ignition of the fuel droplets entrained by the swirling air within the swirl chamber 5, the combustion gases flow through the communicating passage 6 into the main combustion chamber 3 drawing the collected fuel droplets out of the depression 11. Since the collected fuel droplets are drawn out each time after ignition takes place and contribute to diffusion burning in the main combustion chamber 11, carbonization of the fuel droplets collected in the depression 3 will not take place, which would cause smoke emission. Thus, with the depression 11 and the rounded lip 6a, carbonization of fuel droplets in the swirl chamber 5 which would cause smoke formation is prevented because all of the fuel droplets failing to be entrained in the swirling air are collected in the depression 11 and such collected fuel droplets are completely drawn out of the depression into the main combustion together each time when the combustion gases flow into the main combustion chamber 3 through the passage 6.

As described above, the engine performance at low engine speeds has been improved according to the invention. Under engine operation at high speeds, strong swirl is formed which is enough to carry all of the fuel injected from the fuel nozzle. Thus under this condition, fuel droplets will not drop into the main combustion chamber 3 flowing along the passage wall.

When the engine runs at high engine speeds, the depression 11 will not receive the fuel droplets because the swirling air motion under this engine operating condition is strong enough to carry substantially all fuel droplets.

Referring to FIG. 4, the embodiment illustrated herein differs from the FIG. 3 embodiment in that a cylinder head 4 is formed at the inner wall thereof a depression 12 communicating with a passage 6. The depression 12 consists of such a cavity as to help subsequent combustion gases from the passage 6 in diffusing in the main combustion chamber 3. Thus, sufficient diffusion burning is possible and formation of unburnt products can be reduced considerably. In addition to this, since the combustion continues within the depression 12 disposed below a depression or trough 11 to increase the temperature of the trough walls, the evaporation of the collected fuel droplets within the trough 11 may be prompted by this heat so that engine performance at idling operation can be improved.

Preferably as shown in FIG. 5, an exhaust port 14 cooperable by an exhaust valve 13 is located with the area within the interior wall of the cylinder head 4 where a depression 12 is formed so as to facilitate the scavening of the exhaust gases from the main combustion chamber 3 through the exhaust port passage 14. This is advantageous in improving fuel economy.