# Fuel and Combustion



## Ramnares P.E. (Feb 26, 2013)

I've started preparing for the PE exam with Thermal/Fluid depth using the MERM. I'm currently working through the Fuel and Combustion problem section of the Thermodynamics chapter and I've noticed that the Lindeburg 1. Has a fairly large number of problems dedicated to this, 2. The questions are lengthy and sometimes complicated, 3. The SMS for Thermal/Fluids doesn't ask questions that are similar.

Does anyone have any input on the stoichiometric fuel/combustion questions that show up on the exam?

Thanks!


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## ongreystreet (Feb 26, 2013)

I would look at 6 minute solutions and practice exams to get a better idea of the proportion and types of fuels questions that might be asked.

I passed first try and really still don't know that subject well enough to solve most problems, the MERM practice guide sometimes makes certain sections seems more daunting than they will be on the test, compressible aerodynamics is a good example of that, large practice section if I remember, very unlikely to ask a question on the test, and if they do it will probably be much more simple than the majority of practice problems.


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## ikesdsu (Feb 26, 2013)

The two times I took the test there were no combustion/ stoichiometric questions. If they did throw some of those in, they would have to be way easier than what was in the MERM.


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## Ramnares P.E. (Feb 26, 2013)

Thanks guys, it was daunting working through that section to say the least! I know mapuatech said he worked through those sections till he got 100% right and I can now appreciate the effort he put in. The stoichiometric problems are seriously kicking my...


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## ongreystreet (Feb 26, 2013)

The other problem with that section, like compressible aerodynamics, is that it isn't cumulative, knowing combustion and fuels won't help you understand other subjects on the test, meaning it's only worth studying after you get the big stuff down (basic fluids, pumps, basic thermo, cycles, systems, refrig, heat transfer, etc).


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## mizzoueng (Feb 27, 2013)

If you understand the basics of performing a chemical reaction balance, then you will be okay.

As for combustion, understanding the mass/energy balance will answer all of those questions.


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## MapuaTech (Feb 27, 2013)

we cant discuss the actual questions showed up in past exams.

my tip is this, study and oberved the types of fuels used in combustion. Notice that they have different products when reacted with air. And you will observe in merm what products should be expected for every types of fuel. From that, write the reaction equation and do the balancing. Calculation of theoretical and actual ratios will follow. practice practice and practice


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## Ramnares P.E. (Feb 27, 2013)

Sorry, I was not asking for the specific questions. I'm more concerned with the quantity and extent of the combustion questions. Lindeburg dedicates a large number of sample problems, so I was wondering if the test had a large number of combustion questions for Thermal/Fluids (not sure if I'm allowed to ask that)? Also, the Lindeburg questions are incredibly detailed, some with 2-1/2 page solutions which I doubt can be replicated in the exam.


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## ongreystreet (Feb 28, 2013)

Don't expect many on exam, look at practice tests, they will give you a rough idea of subject distribution. In Lindeburg, I only read the 1 hour problems, and din't solve any. When I was done going thru all my sections, I'd go back and take a look at those a bit more.


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## mizzoueng (Mar 1, 2013)

Well, if you are taking the thermo/fluids breadth, odds are in your favor.

I think what you are wanting to know is if there will be as many in depth combustion questions where you have to calculate the stoiciometric contents of different fuels and then blah blah blah blah.

A someone who just passed the oct 12 exam, I can tell you that I studied a lot and came to the conclusion that remembering that almost all problems can be reduced to a mass/enthalpy balance. Chemical balances are good to study as sometimes those popped up in the 6 minute problems.

Also, remember that no matter what, you should be able to answer a question in under 6 minutes. If you find yourself spending a lot of time on a problem, just skip it and come back later. No need fluttering yourself and wasting valuable time on something you may simply be over thinking. A common practice in problems produced by NCEES, which are used extensively in the study guides they sell, is that other problems on the test are based on the previous ones, sometimes you can gleam a solution from the later problems for and earlier one.

Lastly, just take a breath and calm down.


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## Jonhnny123 (Mar 2, 2013)

I think I encountered 2 combustion type problems. It's a weak area for me and I didn't bother studying it, since I thought it would be better to reinforce topics I already knew than try to learn a new subject. For one of the questions, I spent just a couple minutes on it and was able to solve it by following steps in the MERM. The other, I just guessed.

ongreystreet makes a great point. This is one of those "stand alone" topics, it doesn't really build on anything else. So don't get too worried if you're not 100% on this topic.


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## buffteya4 (Apr 18, 2013)

The types of Fuels and Combustion questions encountered on APR 2013 TF PE exam were a bit more complicated than the MERM reference tables had to offer.


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