Internal-combustion engines – Two-cycle – Whirl through piston-controlled ports
Patent
1991-10-11
1993-04-20
Okonsky, David A.
Internal-combustion engines
Two-cycle
Whirl through piston-controlled ports
123432, F02B 7502
Patent
active
052032884
DESCRIPTION:
BRIEF SUMMARY
The invention concerns an internal combustion engine of the two-stroke type with a compression-ignition of Diesel type, which comprises at least one cylinder devoid of lateral ports and at least one piston undergoing a reciprocating motion in this cylinder and delimiting with the latter and with a cylinder head a combustion chamber of variable volume, said cylinder head carrying at least one inlet valve and at least one exhaust valve respectively adapted to an air inlet pipe and to an exhaust pipe for the exhaust gas, the axis of the or each inlet valve making with the axis of the cylinder an angle approximately between 30.degree. and 60.degree. so that the stem of this valve is at a greater distance away from the axis of the cylinder than the head of the valve and this head being placed at the inner end of an at least partly cylindrical recess of the cylinder head into which recess a fuel injector discharges and whose depth increases in a regular manner from the periphery toward the center of the combustion chamber without constituting a constriction toward the latter so that, when this valve is open, it allows a flow on only about one half of its periphery in directing the air toward the piston during the scavenging along and in the vicinity of the generatrix of the cylinder which is the most remote from the exhaust valve or valves, the engine being provided with means for starting it up and operating it at low power.
The invention therefore excludes engines having a controlled ignition since their combustion chambers are fed by a homogeneous mixture of air and fuel preformed in a carburettor or by injection in the inlet pipe during the filling stage of the engine, so that there is no problem of the homogenization of the mixture in the combustion chambers.
An engine of the type defined in the preamble is described in U.S. Pat. No. 4,162,662 and the means for starting it up and operating it at low power are described in particular in U.S. Pat. No. 4,995,348.
An object of the invention is to achieve a satisfactory compromise between the following two requirements which will be studied in succession hereinafter:
a) achieve a good scavenging when the piston is in the vicinity of the bottom dead center (BDC) and the inlet and outlet valves are simultaneously opened;
b) permit, by perfecting in this respect the engine described in the aforementioned U.S. Pat. No. 4,162,662, a rapid combustion with high efficiency when the piston is in the vicinity of the top dead center (TDC) and the inlet and exhaust valves are simultaneously closed.
As concerns first of all the scavenging, the cylinder head must be as permeable as possible, i.e. it must allow through the maximum amount of fresh air for a given pressure difference between the inlet and the exhaust, and the efficiency of the utilization of the air (designated by "trapping efficiency", i.e. the ratio between the mass of fresh air retained by the working chamber and the mass of fresh air passing through the inlet valve) must be as high as possible. When the two-stroke engine is supercharged by a turbo-compressor unit whose turbine is driven by the exhaust gases, satisfying the two criteria defined hereinbefore is more particularly advantageous. Indeed, the energy balance of the supercharging turbine is then improved, which permits reducing the pressure difference between the inlet and the exhaust of the engine and consequently improving the air/fuel ratio by permitting an improved combustion. Indeed, by reducing the aforementioned pressure difference,
1--the dilution of the exhaust gases fed to the turbine is reduced, which permits increasing the pressure of the supercharging air (greater energy on the upstream side of the turbine);
2--the expansion rate of the turbine is increased, which increases the supercharging pressure and therefore the pressure of the air in the cylinder;
3--the pressure in the cylinder (which is closer to the supercharging pressure since the inlet-cylinder-exhaust pressure difference is decreased) is increased.
As concerns now the combus
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Andre Thierry
Edelmann Henri B.
Melchior Jean
Okonsky David A.
S.N.C. Melchior Technologie
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