GB2376502A

GB2376502A - The concept of zero to negative exhaust lead in two cycle engines employing the Kadenacy effect

Info

Publication number: GB2376502A
Application number: GB0110373A
Authority: GB
Inventors: Martin Leonard Stanley Flint
Original assignee: Individual
Current assignee: Individual
Priority date: 2001-04-27
Filing date: 2001-04-27
Publication date: 2002-12-18
Also published as: GB0110373D0

Abstract

The invention applies to improvements to the Kadenacy Effect employed in Two Cycle engines, and in particular to Two Cycle Double Acting Barrel Engines of the Hermann type that employ the Uniflow Open Top Sleeve Valves and piston movement to control inlet and exhaust valve timing. It is this Sleeve Valve control, in conjunction with reciprocating piston motion, that permits the concept of "Zero to Negative Exhaust Lead". This concept, when combined with the rapid opening and closing of the Exhaust Port in less than 1/300<SP>th</SP> of a second, before the Inlet Port is opened, that creates the Kadenacy Effect over a wider operating speed range than hitherto. (The Kadenacy effect is the drawing in of cool fresh air by the depression created by the very high velocity of the out-rushing mass of the exhaust gas of the previous cycle.)

Description

THE CONCEPT OF ZERO TO NEGATIVE EXHAUST LEAD IN TWO CYCLE ENGINES EMPLOYING THE KADENACY EFFECT The invention applies to improvements to the Kadenacy Effect employed in Two Cycle engines, and in particular to Two Cycle Double Acting Barrel Engines of the Hermann type that employ the Uniflow Open Top Sleeve Valves and piston movement to control inlet and exhaust valve timing. It is this Sleeve Valve control, in conjunction with reciprocating piston motion, that permits the concept of "Zero to Negative Exhaust Lead". This concept, when combined with the rapid opening and closing of the exhaust port, before the inlet port is opened, that creates the Kadenacy Effect over a wider speed range than hitherto.

To provide an understanding of how the above mentioned invention can be used in a Two Cycle Double Acting Barrel Cam Engine of the Hermann type using a Uniflow Sleeve Valve arrangement, is shown in Figures 1 and 2.

In addition to this invention, the engine design shown in Fig. 1 incorporates many other ideas and mechanisms already tried and tested on more conventional engine types, but not it is believed in a Two-Cycle Double Acting Barrel Cam Engine of the Hermann type using a Uniflow Sleeve Valve arrangement.

There has always existed the knowledge that if the TwoCycle engine could, successfully, in practice, give the same power from its expansion stroke as is obtained on the Four-cycle engine, the competition between the Two and Four-cycle would be over and the Two-cycle engine would command the market. The only factors that have prevented the Two-Cycle engine from giving double the power, for its equivalent capacity, of a Four-Cycle engine, have been the impurity of the air charge and high internal temperatures.

In a conventional Two-Cycle engine with porting arrangements of the cross, loop and uniflow families, the scavenging process consists of first releasing the exhaust gases so that the cylinder pressure is reduced to below scavenging air pressure, then delivering the fresh air charge. This sweeps out most of the remaining residual and inert gases, then fills the cylinder with compressed air. In an ideal scavenging process the

pressurised air acts like a piston in pushing the burnt gases out of the cylinder without actually mixing with them. However, in practice there is always some contamination of the incoming compressed air charge by the previous cycles exhaust gas remnants.

Michael Kadenacy, researching in the 1930's at the Armstrong-Whitworth company, worked on ways of overcoming these problems of impurity of the air charge and high internal temperatures. He discovered that if the period of the exhaust opening and closing was less than a 1/300th of a second, the speed of the exhaust gas exchange from the cylinder to atmosphere was extremely rapid. Guidelines extracted from his work identified that if the exhaust port area is equal to the piston bore area, and the exhaust duration is less than a 1/300th of a second, then a depression is created within the cylinder to approximately 0.3 bar.

This depression is rapidly replaced with about 0. 7 bar (10.1 psi) boost of clean, uncompressed cool fresh air at atmospheric pressure and temperature. He called his discovery the"Kadenacy Effect" In engines employing the Kadenacy Effect, the fresh air charge is not called upon to push out any of the exhaust gases, as is the requirement on conventionally scavenged Two-Cycle engines. On the contrary, clean uncompressed cool fresh air is drawn by the depression created by the very high velocity (approximately 1380 m/sec) of the out-rushing mass of the exhaust gas of the previous cycle. Kadenacy's effect can be at its most beneficial when an exhaust port is rapidly opened and closed in less than 1/300 sec as late as possible in the expansion stroke.

The significance of this phenomena is, that the incoming air at atmospheric pressure, is not heated by any compression, neither is there any residual exhaust gas remaining in the cylinder from the previous cycle to contaminate an incoming charge. The real benefits are that this incoming charge of pure cool air at atmospheric pressure and temperature comes without any expenditure of energy by the engine.

Although there are no records of Kadenacy measuring emissions, if his work could be repeated and measured today, there are likely to be some reductions to emissions, especially N02 measurements. The inducted

pure cool air charge, with its greater weight of oxygen, enables the molecules of fuel injected to find their oxygen more readily. This results in more efficient and cooler combustion. If the low exhaust temperatures (320 C) recorded by Kadenacy in his experiments at peak Bmep are an indication of lower combustion temperatures then it is a reasonable assumption expect that the N02 emissions would be lower. The benefits of these attributes have also resulted in lower peak cylinder pressures being of the order of 10% less, whilst at the same time the mean effective pressures and BHP have been approximately 60% higher.

To achieve the benefits from the Kadenacy Effect the following points should be considered :- * Exhaust lead * Rapid exhaust valve opening and closing * Streamlining the flow passages * Exhaust tuning and elimination of the effect of reverse flow of exhaust gases.

This Patent Application recognises these points with one exception. That exception is Exhaust Lead and this requirement is replaced by the concept of"Zero to Negative Exhaust Lead"i. e. the Exhaust Port 1 is closed before the Inlet Port 4 is opened, (See Fig. 3 & 4), rather than in the case of conventional Two-Cycle engines, whereby both exhaust and inlet ports are open for a period of time together to allow scavenging. i. e. Positive Exhaust Lead (See Fig, 5). Normally, Exhaust Lead period is measured in output shaft degrees.

For additional understanding of Kadenacy's work see GB Patents ranging from 308593 to 48865 circa years 1930 to 1940 and US Patents 2102559 to 2148249.

The concept of"Zero to Negative Exhaust Lead" considers two aspects of Exhaust Lead with reference to the relevant positions of the Sleeve Valve and Piston towards the end of the expansion stroke (See Fig. 3).

Firstly, what is meant by"Zero Exhaust Lead", is that the exhaust port is just closed by the returning sleeve valve at the same instant as the descending piston top exposes the upper edge of the inlet ports. This is the ideal state whereby expansion stroke has been maximised and the piston is at its lowest position in the expansion phase of the Two cycle process (See Figs. 6).

Secondly,"Negative Exhaust Lead"means that exhaust port has closed a little earlier and the piston has to descend a little further, prior to the upper edge of the inlet port being exposed to the inrush of cool air at atmospheric or boosted pressure. This, perhaps is a more practical approach, which sacrifices a very small amount of expansion whilst providing a little extra time for the high speed desmodromic action of the Sleeve Valve Rotary Actuator device. i. e. 1/300 sêcond or less (See Fig, 7) Another, and the most important feature, is to ensure that the high speed operation of Sleeve Valve movement is independent of the Barrel Engines output shaft. This means that the actuation of the Sleeve Valve occurs at

1/300th of a second or less regardless of output shaft rpm, thus creating the"Kadenacy Effect"over a wide speed range.

Micheal Kadenacy realised the limitation of narrow speed range and attempted to overcome this (See US Patent No 2113480). It is not known if this mechanical solution was ever built and operated.

It is the concept of"Zero to Negative Exhaust Lead" and the fast operation of the Sleeve Valve and it's independency of the output shaft, that provides the capability of trapping a depression regardless of engine speed. This suggests that"Kadenacy Effect" could operate over a wider rpm range than hitherto. Moreover, it would still enable an engine to start and operate without the costly need of a scavenge blower and its drive, as required with other Two Cycle engines. This feature presents both a significant technical and economic benefit.

In order to achieve the reliable opening and closing of the sleeve valve in the operating time necessary to create the"Kadenacy Effect", the Sleeve Valve requires a positive opening and closing in a rapid manner. This can be achieved in this invention by using a"Piezo-Electric-Hydraulic servo control to switch hydraulic pressure to a Rotary Actuator".

Piezo-Electric-Hydraulic operating devices are used on 2nd generation Common Rail Fuel Injection systems and are chosen for their rapid response times of 0. 1 msec. The timing of the Piezo-Electric-Hydraulic Rotary

Actuator is controlled by the engine ECU which also controls the timing of the Common Rail Fuel Injection system.

Fig. 1 Two Cycle Double Acting Barrel Cam EngineLongitudinal Section.

Fig. 2 Two Cycle Double Acting Barrel Cam EngineSections XX, YY and View A Fig. 3 Shows the Exhaust Port open and the Inlet Port closed.

Fig. 4 Shows the Inlet Port open and the Exhaust Port closed.

Fig. 5 Shows the port area diagrams for Positive Exhaust Lead Fig. 6 Shows the port area diagrams for Zero Exhaust Lead Fig. 7 Shows the port area diagrams for Negative Exhaust Lead.

Claims

CLAIMS 1 The employment of the "Zero to Negative Exaust Lead concept to the rapid opening and closing of an exhaust port in a Two-Cycle Double Acting Barrel Cam Engine of the Hermann type using a Uniflow Sleeve Valve arrangement shown in Fig. 1 and 2. This action creates the"Kadenacy Effect". The Open Top Sleeve valve is actuated to both open and close the Exhaust Port independantly of output shaft rpm. The actuation must be rapid and in a controlled manner, and be within a duration of less than 1/300 of a second (3.33 milliseconds). This rapid opening and closure of the Exhast Port must be completed towards the end of an expansion stroke and immediately before the Inlet Port is opened by the top edge of the piston as it approaches BDC. By these actions, the"Kadenacy Effect"provides a trapped depression in the operating cylinder over the engines operating speed range.
2 Improvements resulting from Claim 1 in the Brake Thermal Efficiency (BTE), Brake Mean Effective Pressure (BMEP), whilst achieving higher and smoother Torque characteristics, lower exhaust temperatures and lower levels of emissions of both naturally aspirated (NA) and pressure charged and interceded engines of the Two or Four Cycle type 3 Any Two-Cycle Double Acting Barrel Cam Engine being fueled by Diesel, DME, Syntrolium, Gasoline, HC Gas or Hydrogen, having a plurality of the inventions set forth in any one of the preceding claims 1 and 2.