# Otto and diesel cycle

In case of Otto cycle we consider that heat is immediately added to air fuel mixture(i.e constant volume heat addition) but in case of diesel cycle we consider heat addition at constant pressure and we also talk of cutoff ratios.why so??

russ_watters
Mentor
In case of Otto cycle we consider that heat is immediately added to air fuel mixture(i.e constant volume heat addition) but in case of diesel cycle we consider heat addition at constant pressure and we also talk of cutoff ratios.why so??
There are pros and cons to each. have you done a google search for this question?

In case of Otto cycle we consider that heat is immediately added to air fuel mixture(i.e constant volume heat addition) but in case of diesel cycle we consider heat addition at constant pressure and we also talk of cutoff ratios.why so??
http://charming.awardspace.com/otto_diesel/otto_diesel.html
In this website you can find explanations about the diesel engine, how and why it was developed,etc..
I read in an article that Rudolf diesel initialy used coal powder as fuel(sprayed over hot compressed air)but the combustion increased the pressure higher than the permissible limits so that the cylinder exploded during a trial.Later petroleum oil was used and the fuel was injected at lower rates so that combustion occurs approximately at constant pressure rather than constant volume.