Internal-combustion engines – Multiple cylinder – Having rotary output shaft parallel to cylinders
Patent
1992-05-27
1993-06-15
Okonsky, David A.
Internal-combustion engines
Multiple cylinder
Having rotary output shaft parallel to cylinders
123 58A, F02B 7526
Patent
active
052189333
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to internal combustion engines of two stroke or four stroke type and is concerned with that type of engine which includes at least one piston which is reciprocably received in a cylinder and which is coupled to a rotary output shaft by a coupling which converts the reciprocal movement of the piston into rotary movement of the output shaft, the engine being so arranged that, in use, the fuel/air mixture in the or each cylinder ignites at a predetermined time in the operating cycle of the engine, which will be referred to herein as the ignition time. The invention relates also to a method of operating such an engine.
In conventional engines, the output shaft constitutes a crankshaft and the coupling between the or each piston and the output shaft constitutes a respective crank which is rigidly connected to the output shaft and rotatably coupled to a piston rod which is in turn connected to the piston by a connection which permits at least limited relative rotational movement. The use of such a crankshaft is of course long established and well proven and has the inevitable consequence that the position and speed of the or each piston at any movement is precisely determined by the geometry of the associated piston rod and crank and is wholly independent of the progress and nature of the combustion process within the cylinder.
The efficiency of operation of an internal combustion engine is governed by a large number of interrelated complex factors and these include the completeness and speed of the flame propagation through the air/fuel mixture and the relationship between the instantaneous position of the piston and the progress of the combustion process.
Since, in a conventional engine, the instantaneous position of the piston is determined solely by geometrical considerations, as explained above, efforts must be made to match the progress of the combustion process to the movement of the piston. Ignition of the fuel air mixture, whether by a spark in a spark-ignited engine or due to compression in a diesel engine, occurs at a predetermined point which is typically 5.degree. to 40.degree. before the top dead centre postion (TDC). Combustion of the fuel takes places from the ignition point until anything up to typically about 40.degree. after TDC. Combustion of the fuel takes place in two indistinct overlapping stages, the first of which is flame propagation in which the flame spreads from the point at which ignition initially occurs throughout the entire air/fuel mixture and in the second of which the fuel is actually burnt and the power output of the engine is produced. In a conventional engine it is desirable that the flame propagation is essentially complete before TDC and since the rate of flame propagation is an inverse function of the pressure of the air/fuel mixture this places a practical limit on the maximum compression ratio that can be used and necessitates the use of additional measures to maximise the rate of flame propagation before the increasing pressure of the air/fuel mixture results in a significant decrease in the flame propagation rate. Thus whilst it is desirable to increase the compression ratio because this increases the mean effective pressure (m.e.p.) and thus the power output and also the efficiency of the engine, the factor refered to above places a practical upper limit on the compression ratio. The necessity of maximising the flame propagation rate generally requires the production of swirl and/or turbulence in the air/fuel mixture by the provision of a complex combustion chamber shape, swirl-inducing inlet ports, squish areas and the like, all of which add to the complexity and cost of the engine.
Notwithstanding the various measures referred to above which are generally taken in connection with conventional reciprocating piston engines, the efficiency of combustion still remains relatively low. This results not only in the power output and efficiency of the engine being considerably less than that which would be theoretically achieveable but also in
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Environmental Engines Limited
Okonsky David A.
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