Cylinder Pressure graph

David G · Jun 18, 2015

I found a nice graph of typical cylinder pressures that show the different phases. This graph is clean, but noise before or after the peak would indicate detonation.

<image src="http://forums.yesterdaystractors.com/photos/mvphoto22828.gif"/>

buickanddeere · Jun 18, 2015

Pretty good graph.
Some of these explain the Brayton Cycle that the Otto combustion engine uses. It shows why increasing the compression ratio provides a reduced percent gain in power and efficiency. Any why part load diesel efficiency is lousy compared to full load efficiency.
https://www.google.ca/search?q=rankine+cycle+graph&biw=1280&bih=663&tbm=isch&tbo=u&source=univ&sa=X&ei=ATODVf60Hcix-AH3nIHAAQ&sqi=2&ved=0CBwQsAQ#tbm=isch&q=brayton+cycle+graph+

David G · Jun 18, 2015

This graph shows a representative system. One thing to note is the pressure wave will take a finite amount of time, regardless of RPM but the cycle time varies due to changes in RPM. You have to light the mixture earlier to get the peak pulse to happen at the right position of the crank, thus the need for centrifugal advance. Variable valve timing falls into the same issue, you want to open the valves earlier at higher RPM's. Modern engines get a flat torque curve by varying both the valve timing and ignition timing.

The big natural gas engines I work on are optimum pressure around 15 degrees ATDC, I would imagine most engines are about the same time so the most torque can be applied to the crankshaft.

buickanddeere · Jun 18, 2015

(quoted from post at 18:30:21 06/18/15) This graph shows a representative system. One thing to note is the pressure wave will take a finite amount of time, regardless of RPM but the cycle time varies due to changes in RPM. You have to light the mixture earlier to get the peak pulse to happen at the right position of the crank, thus the need for centrifugal advance. Variable valve timing falls into the same issue, you want to open the valves earlier at higher RPM's. Modern engines get a flat torque curve by varying both the valve timing and ignition timing.

The big natural gas engines I work on are optimum pressure around 15 degrees ATDC, I would imagine most engines are about the same time so the most torque can be applied to the crankshaft.

It's all about area under the curve.

Cylinder Pressure graph

David G

Well-known Member

buickanddeere

Well-known Member

David G

Well-known Member

buickanddeere

Well-known Member

Similar threads