Heat Input and Work Done In A Typical Engine Cycle

[JB63]

Hello all,

As part of a University assignment I have been given the task of creating a model in Microsoft excel to simulate engine pressure based on crank angle position. In order to do this crank angle and corresponding pressure for a Honda engine was recorded under the following 6 conditions:

Motored(No ignition) With Ignition
3000 RPM 3000 RPM
5000 RPM 5000 RPM
8000 RPM 8000 RPM

From this data I have calculated the volume inside the cylinder at any given time (Based on crank angle position), and then taken Logs of P & V and put on an XY scatter graph in order to find the polytropic index of the Compression and Expansion phases (Based on the gradient of the line). One part of the assignment is to simulate this pressure by considering the crank angle position, calculated volume and then using the polytropic index found earlier to find the resultant pressure - Combustion phase is also taken into account, with combustion calculations being used to simulate the extra pressure at this stage.

I am fairly happy with most of the above, however another section of the assignment is to look at heat input and work done, and then apply the first law of thermodynamics to the data which has been acquired. However once everything has been calculated I am ending up with a heat input from combustion of 263 Joules, and work done of approx 1200 Joules (Taking into account compression and expansion phases only) i.e the area under the PV diagram. Looking at the first law, I cannot understand how it is possible to get more work out than was put in.

If anybody has any ideas as to why this is the case, I would appreciate it if you could share your ideas.

If anyone is interested I will also be more than happy to share the engine data I've acquired, and the model itself.


Thanks,

Jordan

 

[EnergyMix]

Your post violates the Eng-Tips forum policies. Please read FAQ731-376, specifically item 9.

In specific answer to your question, either you have discovered a new source of energy and you need to patent it quickly and will retire rich at a very young age or you made a mistake ... which do you think is more likely?

 

[JB63]

Firstly apologies for effectively breaking rule 9 - I should have reviewed the forum policies prior to posting. However, I have exhausted all avenues and am struggling to find the necessary information on the internet. I also feel that the data & model I am offering to share in return for some help could be of a lot of use to some members.

I agree, a mistake is exactly what I have made. I can simulate pressure perfectly, (with use of combustion calculations), but maybe I have heat input in the wrong units or I have not accounted for something else. Apologies for wasting your time I suppose.

 

[EnergyMix]

I suggest you go talk to someone at your University -- your lab instructor, a grad assistant, even your teacher.