OTTO CYCLE DEFINITION 2

[harrisj]

I have researched a number of websites and books to get a definition of the Otto cycle.

In most cases it is synonymous with 4-stroke, and in others seems to be associated only with spark ignition.

My view is that it describes the 4-stroke cycle, whether spark or diesel, reciprocating or Wankel.

Anyone care to comment on this, and put me straight?

 

[strokersix]

The Otto cycle is an ideal thermodynamic cycle with the characteristic of constant volume combustion.

It says nothing about the hardware involved. It is often used as a model for spark ignited engines.

 

[MGaberik]

Yes, Otto describes constant volume heat addition regardless of 2 stroke, 4 stroke, wankel or other method of managing the working fluid. Practical SI engines approach the ideal Otto cycle.
Diesel cycle describes constant pressure heat addition, again regardless of engine mechanical approach.

 

[franzh]

I think I may have missed something. Doesn’t the Carnot cycle more accurately describe the ideal thermodynamic cycle and not Otto?

See as an example:

http://www.grc.nasa.gov/

http://WWW/K-12/airplane/otto.html

I have always believed that the Otto cycle simply describes the events outlined via the PV diagram. In actuality, the Otto cycle is virtually unobtainable, as there are significant friction and heat rejection losses. The Otto cycle can functionally describe the ideal cycle, but the diesel cycle brings other factors in play, as there is no “V” curve, and the 2 cycle combines functions, very broadly covered by the PV 4 cycle graph, with significantly more losses, but regained in additional power strokes.
Franz

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[GregLocock]

The way I heard it - the Carnot cycle is the most efficient, but very diffult to approach in practice, since it relies on some very time consuming processes.

The Otto cycle is an attempt to break the typical SI cycle down into a series of easy to understand/analyse thermodynamic processes

The ideal Diesel cycle is the same sort of approach for a typical CI engine cycle.



Cheers

Greg Locock

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[harrisj]

Thank you all for the posts here. However, I'm still confused. I understand the PV diagrams for idealised engines, and have a reasonable grasp of flame propagation in Diesel and petrol engines.

My problem (maybe where I should have started) is as follows:

A small supplier is offering me a high speed rotary engine which is still under development. It runs on kerosene type fuel, injected into the combustion chamber, and has a spark plug. It runs at a CR of about 15:1 which is high for a petrol engine but low for a diesel. He tells me it runs on the Otto cycle. There is no supercharging.

Possibly this is just a problem of nomenclature, but I feel I should understand what happens in the combustion chamber. This is a mystery to me and apparently to the supplier!

Has anyone come across such an engine?

 

[icrman]

It would be what Mr. Otto originally came up with.
Intake, compression, power, exhaust

 

[strokersix]

The ideal constant volume or Otto cycle is isentropic compression, constant volume heat addition, isentropic expansion, and constant volume heat rejection. This is an IDEAL cycle used for analysis purposes and for a theoretical reference point to understand real cycles.

The real cycle in an engine includes exhaust, intake, and blowdown events as well as heat transfer and a myriad of other processes.

 

[icrman]

I think Mr. Otto was more concerned about the events, and just plain getting it to run. If he was so concerned about the thermodynamic aspects, he would have created a year 2005 formula 1 engine back then. LOL
So instead of Cycle maybe it should be Otto events. Anyway I would suppose some will get what I'm trying to say here.