In internal combustion engines that work with pistons in cylinders there is a certain leakage of gas passing the piston seals out into the crank house. To prevent the gas pressure in the crank house from becoming too high it is therefore necessary to keep this ventilated or open towards the atmosphere or other receiver. The ventilated gases are however heavily polluted by oil aerosol formed by the lubricating oil in the crank house. Thus they carry oil with them. Besides from causing extra oil consumption this also make the gases constitute an environmental problem. Sometimes the latter can be avoided by letting the ventilated gases return to the engine with ingoing combustion air. Sometimes the gases are too polluted for this to be a viable method.
In any case it would be beneficial if one could separate the oil from the gas and return it to the crank house. This would lower the oil consumption and reduce the problems associated with discharge or recirculation of the crank house gases.
The oil however exists in the aerosol in so small droplets that these are difficult to separate out in conventional types of filters or demisters. Filters with sufficient separating capability are prone to clog up. Furthermore the crank house gases are warm so that part of the oil is in the form of vapour and not possible to filter out.
The problems of clogging up and oil in vapour phase can be solved with an oil separator made according to the invention described below. One schematic design is shown in
Instead of using the addition of cold air for cooling, this may be achieved by the extraction of heat from the gas by using cooling devices placed in the turning chamber or its vicinity. For instance cooling devices with an internal flow of cooling fluid or cooling fins in contact with a cooler surrounding may be used. With good enough heat exchange between downgoing and upgoing gas flows it might be sufficient that the turning chamber or the lower part of the device is un-insulated towards a cooler surrounding. The heat transfer here can be increased by means of surface area increasing fins applied both at the inside of the wall and possibly its outside. When cooling is accomplished in such an indirect manner and not through the addition of cold air, the fan 6 (or connection to a low pressure) can be dispensed with. A moderate overpressure in the crank house will then make the gases flow through the device.
Oil is deposited on the heat-exchanging wall 2, where it forms an oil film which by gravity is caused to flow downwards and the oil is collected in the turning chamber from which it is drained through an oil outlet 7.
Separation of oil in the device is caused by several different mechanisms:
a) Oil drops are separated from the gas flow when they collide with the walls. Such collisions are promoted by the walls being not smooth but form patterned in such a way that the gas will flow in a turbulent way. This also promotes a good heat exchange between downgoing and upgoing flows.
b) Oil drops are separated from the flow and deposited on the wall by thermal diffusion. Drops situated in a thermal gradient will be caused to move from hot towards the cold by the molecular movements of the gas. This is especially applicable to small droplets and is of significance when droplets in a warm stream of gas are passing along a cold surface.
c) Oil in vapour phase condenses on a cold wall surface.
The critical and difficult step is for the oil to leave the gas stream. Once this is accomplished the oil is caught by and incorporated into a film of oil which is drained downwards towards cooler parts of the device. Oil separation takes place mainly at the downward passage through the device. That is when the thermal diffusion works in the right direction and when the oil in vapour phase condenses on the cold wall.
During its upward passage through the device the gas is heated by contact with a warmer wall. Those droplets that may have escaped from being separated out during the downward flow of the gas can then, at least partly, be vaporized. Oil in vapour phase sometimes constitutes a lesser problem than oil in drop or aerosol form. When having high gas velocities through the device or when wanting a high degree of separation it can be advantageous to apply several separators of the described type in series after one another. Such oil that is vaporized during the heating phase in an earlier step can then condense during the cooling phase of a later step. After several steps entailing cooling and heating the end result can approach a gas stream without oil drops and a concentration of oil vapour that is governed by the vapour pressure of the oil at the lowest temperature.
A preferred embodiment of the invention is shown in
To make the design easier to understand the bundle 2 in
The two gas flows downwards and upwards gradually change in temperature during their passage through the device. A great advantage is that the heat transfer takes place in counter current flow so that the warmest of the warm flow heats the warmest of the cold flow and that in a corresponding way the coldest of the cold flow cools the coldest of the warm flow. This allows for a high heat exchanging efficiency. The amount of heat that has to be extracted, or the amount of cold air that has to be added in the turning chamber, may then be small and still be able maintain a low temperature in the turning chamber.
In
Above, for the sake of simplicity, has been described a device with a warm upper part and a cold lower part to which the oil is drained. Of course it is possible to orient the device in some other direction for instance so that the oil is drained towards the gas inlet of the device and back to the crank house of the engine, even backwards through the same duct that leads the gases from the crank house. In
It is also possible to dispense with turning chambers and instead divide the gases into two counter current flows that are made to pass through the device. Heat may then be extracted from the middle of the device where the flows change in character from being cooled to being under heated.
Number | Date | Country | Kind |
---|---|---|---|
0500403-1 | Feb 2005 | SE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/SE2006/000226 | 2/21/2006 | WO | 00 | 12/18/2007 |