GB2129873A

GB2129873A - The scavenging of two-stroke internal combustion engines

Info

Publication number: GB2129873A
Application number: GB08329017A
Authority: GB
Inventors: Bodo Wolf
Original assignee: INST ENERGETIK RATIONAL
Current assignee: INST ENERGETIK RATIONAL
Priority date: 1982-11-01
Filing date: 1983-10-31
Publication date: 1984-05-23
Also published as: HUT35778A; GB8329017D0; CS258021B1; BG46404A1; IT1162980B; PL244327A1; DD210409A3; FR2535391B3; FR2535391A1; IT8368139A0; DE3338568A1

Abstract

Scavenging air is supplied direct to the combustion chamber via an inlet opening or openings before air fuel mixture is supplied to the combustion chamber via a transfer passage and port(s) from the crankcase. Where a plurality of inlet openings are provided, they are spaced laterally and/or longitudinally of the combustion chamber and are closer to the exhaust ports than are the transfer ports.

Description

SPECIFICATION Scavenging of two-stroke internal combustion engines The invention can be used in the construction of two-stroke spark-iginition or compressionignition engines.

Scavenging and charging of two-stroke internal combustion engines takes place via inlet and exhaust ports. If central and centrifugal lubrications are used, scavenging is accomplished after the expansion stroke by the air sucked from the crankcase. The fuel is in this case usually injected by blowers. These engines have a high consumption of lubricating oil. The injection represents additional technical outlay.

Also known are solutions in which mixtures of fuel, air and lubricating oil prepared in carburettors are sucked in through inlet ports. These mixtures then scavenge the cylinders of the engines. In this process on the one hand the unused fuel-air mixture is exhausted with the exhaust gases from the engine, and on the other hand complete removal of the exhaust gases from the cylinders is sacrificed in order to reduce these losses due to imperfect scavenging. This leads to losses in power.

As a consequence several suggestions were made for utilising the transfer ports to create an air cushion between the exhaust gas and the fuelair mixture. These solutions have not fulfilled expectations in practice. The suggestion according to patent specification F 02 B 25/14 No. 2 919 172 proceeds from the engine working with at least three transfer ports between the crankcase and cylinder for the charging of the cylinder; the parts nearest to the exhaust port sucking in air with lubricating oil through the crankcase while the required fuel is charged into the central port. All these suggestions require devices which have not yet been, on the one hand, tested in mass-produced two-stroke engines and, on the other hand, ignore million times tested and proven process steps.

The aim of the invention is to reduce losses due to poor scavenging, and oil consumption in twostroke engines and thereby to reduce fuel consumption.

Technical reasons for the high losses due to poor scavenging in carburettor-charged twostroke engine may have their origin in the fact that as a scavenging gas a largely homogenous mixture of fuel, lubricating oil and air is sucked into the cylinder, through the inlet ports. Because for reasons of a high power output the removal of the expanded exhaust gases from the cylinders should be as complete as possible and a high turbulence of gases is obtained during scavenging, in operation with a carburettor these losses due to poor scavenging are not to be reduced significantly.

The aim of the invention is to propose a variant which can be technicaily realised, which ensures the long-sought air cushion between the exhaust gases and the fresh mixture during the strokes "scavenging" and "charging" with the highest effectivity and the most extensive retaining of the proven process steps and method steps.

This is achieved according to the invention in that a part of the air needed for the complete combustion of the fuel, by-passing the crankcase and the carburettor or injection means, is fed directly into the combustion space through inlet openings separated transversely to the direction of stroke and/or arranged at different stroke levels in the cylinder wall, this partial stream of air flowing through inlet openings which are nearest to the exhaust opening of the cylinder and/or to the upper dead centre of the piston, while the mixture of fuel, air and possibly lubricating oil continues to be delivered into the combustion space in a known manner via the crankcase and one or more transfer ports, the inlet openings of which are more remote from the exhaust port or ports and/or the upper dead centre than the inlet opening for the partial stream of air.

The concentration of fuel in the mixture should be so adjusted that, related to the air which is present in the cylinder at the end of scavenging, air numbers are achieved which are comparable to the present state of the art.

This ensures that the first scavenging stream is air while the stream of mixture enters the cylinders only afterwards and lubrication of the engine is ensured by a lubricating oil concentration which is smaller having regard to the whole amount of gas sucked in.

According to the invention complete combustion, using scavenging air present in the cylinder, is assisted by controlling the outlet opening for the scavenging air and the fuel air mixture in the cylinder wall and/or the pressures of the mixtures.

The solution according to this invention is described in comparison with a conventional twostroke internal combustion engine.

The total amount of air needed for combustion is sucked in through an air cleaner known per se.

Thereafter, paying due consideration to the flow and saturation pressures, 50 to 80% of the air needed for combustion are delivered through the inlet port or ports nearest to the upper dead centre of the piston directly into the cylinder. The remaining partial stream of air, which, if maximum power output is required, is loaded with fuel from the carburettor or with diesel oil up to the point of saturation, is fed into the cylinder through a carburettor or through a continually operating injection nozzle in a manner known per se via the crankcase through the inlet ports or port parts nearest to the lower dead centre of the piston. The necessary lubrication in the crankcase, when using fuel supplied via a carburettor, may be ensured in this arrangement with less than half of the lubricating oil compared to comparable conventional two-stroke engines. Compared to conventional two-stroke spark-ignition engines the solution according to the invention may save lotto 15%offuel.

Claims

1. A method for the scavenging of a two-stroke internal combustion engine having a cylinder, a crankcase, a reciprocable piston, an inlet port, an exhaust port, all constructed, arranged and adapted to operate substantially in a manner known per se, wherein a part of the air needed for the complete combustion of the fuel is fed into the combustion space, which is defined by the cylinder and piston, directly through at least one air inlet opening in the cylinder wall situated at a level above the level of the inlet opening of the transfer port but below the level of the upper dead centre of the piston.

2. A method for the scavenging of two-stroke internal combustion engines having one or more cylinders, using scavenging with air and mixture of air, fuel and possibly lubricating oil supplied, via the crankcase through the transfer ports between the crankcase and the cylinder and openings in the cylinder wall of the engine uncovered and covered by the piston, into the combustion space defined by the cylinder and piston, wherein a part of the air needed for the complete combustion of the fuel by-passes the crankcase and the carburettor or injection means and is fed directly into the combustion space through inlet openings separated transversely to the direction of stroke and/or arranged at different stroke levels in the cylinder wall, this partial stream of air flowing through inlet openings which are nearest to the exhaust opening or openings of the cylinder and/or to the upper dead centre of the piston, while the mixture of fuel, air and possibly lubricating oil continues to be delivered into the combustion space in a known manner via the crankcase and one or more transfer ports, the inlet openings of which are more remote from the exhaust port or ports and/or the upper dead centre of the piston than the inlet openings for the partial stream of air.

3. A method according to Claim 1 or 2, wherein a fuel-air-lubricating oil mixture is used which is excessively rich to such a degree that it is completely burnt by using scavenging air present in the cylinder.

4. A method according to Claim 1, 2 or 3, wherein scavenging and charging openings in the cylinder wall and/or the pressures of the air and/or fuel-air-lubricating oil mixture are controlled at the inlet openings.

5. A method according to Claim 1 or 2, substantially as herein described.

6. A two-stroke internal combustion engine having a cylinder, a crankcase, a reciprocable piston, an inlet port, an exhaust port and a transfer port, all constructed, arranged and adapted to operate substantially in manner known per se, comprising at least one air inlet opening in the cylinder wall situated at a level above the level of the inlet opening of the transfer port but below the level of the upper dead centre of the piston, the air inlet opening serving for feeding a part of the air needed for the complete combustion of the fuel directly into the combustion space defined by the cylinder and piston.

7. An engine according to Claim 6, constructed, arranged and adapted to operate substantially as herein described.