In my Thermodynamics class, I was assigned a project to model a 4 stroke engine as an ideal Otto cycle. I chose to model the EX250J's engine since I have a 2009 Ninja 250R. I was hoping the people of this forum are able to assist me with this project.

Some information I already know are the compression ratio, bore, and stroke. One essential information that I can not find, but need to know is the pressure, temperature, and volume of the air + fuel mixture in the a cylinder when it the piston at it's bottom dead center. Or even the pressure, temperature, and volume of the fuel + air mixture the moment after ignition when the piston is at the top dead center. I also need to know the max and minimum temperature of the mixture.

Any help would be greatly appreciated. Thanks!

In my Thermodynamics class, I was assigned a project to model a 4 stroke engine as an ideal Otto cycle.................Any help would be greatly appreciated. Thanks!

Welcome to Ninjet.org, Leslie !!! :grouphug:

The parameters at the top bottom dead center should be close to ambient conditions.

As the compression is adiabatic, you could calculate the conditions at the top dead center assuming an ideal gas with zero heat transfer.

http://en.wikipedia.org/wiki/Otto_cycle

http://web.mit.edu/16.unified/www/SPRING/propulsion/notes/node25.html

Ideal versus real engine:

http://web.mit.edu/16.unified/www/SPRING/propulsion/notes/fig5OttoIdeal_web.jpg

http://web.mit.edu/16.unified/www/SPRING/propulsion/notes/fig5OttoReal_web.jpg

Welcome to Ninjet.org, Leslie !!! :grouphug:

The parameters at the top bottom dead center should be close to ambient conditions.

As the compression is adiabatic, you could calculate the conditions at the top dead center assuming an ideal gas with zero heat transfer.

http://en.wikipedia.org/wiki/Otto_cycle

http://web.mit.edu/16.unified/www/SPRING/propulsion/notes/node25.html

Ideal versus real engine:

http://web.mit.edu/16.unified/www/SPRING/propulsion/notes/fig5OttoIdeal_web.jpg

http://web.mit.edu/16.unified/www/SPRING/propulsion/notes/fig5OttoReal_web.jpg

Thanks. Would you happen to know actual values at each of the strokes? The professor actually wanted us to find all the valeus at each of the strokes and calculate the MEP and efficiency. If I have the temperature and pressure values at one of the strokes and the maximum temperature of the cycle, I can get all the other values.

How the heck does one obtain actual values?

You sure the prof isn't messing with your head?

The temperature varies throughout the volume and with time (although assume an instant at both TDC sand BDC).

I hated thermo. But I may be of some help here.

Volume of cylinder at BDC: The only thing you don't know is the volume of the space between the top of the piston and the bottom of the head. The rest of it is just volume of a cylinder, using the bore and stroke for dimensions. Approximate it.

Temp of air+fuel mix: For ease, I would assume that it's the same temp as the incoming air from outside. (it won't be because of pressure changes in the carbs and intake valves, along with heat transfer from the cold fuel, but let's keep this simple and not require a CFD analysis).

Volume at TDC: You have the CR. You know that it compresses the initial volume of fuel+gas by a factor of 12.5:1. So take your initial volume and divide by CR.

You should be able to solve for everything else, including max temp. IIRC, the idealized T-S diagrams and P-V diagram should be helpful.

I hated thermo. But I may be of some help here.

Volume of cylinder at BDC: The only thing you don't know is the volume of the space between the top of the piston and the bottom of the head.

Can't one calculate that if one knows cylinder displacement and compression ratio?

Thermo wasn't my favorite, either!

Can't one calculate that if one knows cylinder displacement and compression ratio?

Thermo wasn't my favorite, either!

Yes, I think so.

V_i - change in V = V_f
V_i / 12.5 = V_f

and change in V can be found from the bore and stroke, leaving us with 2 equations and two unknowns.

or something like that.
Then use PV=RT=constant to determine the change in pressure during the compression stroke.

amiright? it's been a while.

Thanks. Would you happen to know actual values at each of the strokes? The professor actually wanted us to find all the valeus at each of the strokes and calculate the MEP and efficiency. If I have the temperature and pressure values at one of the strokes and the maximum temperature of the cycle, I can get all the other values.

For your 2010 model, these are the values for one cylinder:

http://en.wikipedia.org/wiki/Kawasaki_Ninja_250R

Bore and Stroke: 62.0 mm × 41.2 mm
Compression Ratio: 11.6:1

The displacement volume (independent from the dead space at TDC) = Area of cylinder (bore) x stroke = (6.2 x 6.2 x Pi x 4.12) / 4 = 124.39 cm^3

Volume of combustion chamber at TDC = 124.39 / 11.6 = 10.72 cm^3

OOPS! I forgot that the newgen has a lower compression ratio than the pregen.


SSHHHhhhh Hernan, don't do the math for the OP! Give the equations, not the work. :p

EDIT: I really hate how over simplified the math has to be and how many assumptions have to be made in order to use the idealized cycle and the idealized P-V and T-S diagrams. Bleh. Just take CFD and let the computer do the hard work. On the other hand, leslieliang does your university use EES?

..........
SSHHHhhhh Hernan, don't do the math for the OP! Give the equations, not the work. :p
............

:angel: :angel: :angel:

Initial volume for compression and exhaust strokes or final volume for admission and work strokes = 124.39 + 10.72 cm^3 = ???

This may or may not help, it's the notes from my previous professor from his current section this semester. It's basically an overview of all the assumptions and gas law relationships for an Otto cycle.

You guys are scaring me now.

So my professor said I can assume that the intake stroke's pressure and temperature are atmospheric, given the engine is started at sea level on a nice normal sunny day, etc. The problem now is the max temperature. I have no idea what the temperature of the air-gas mixture is when it ignites. Does anyone have information on that?

Idle is about 350 when I go full throttle 1000~1200 is normal
Nitrous sends it close to 1400. If it goes over 1500 it melts plug tips.

...........The problem now is the max temperature. I have no idea what the temperature of the air-gas mixture is when it ignites. Does anyone have information on that?

What increases the temperature?

1) Adiabatic compression of ideal gas.
2) Combustion heat of the stoichiometric mix that fits inside the big volume at BDC.

http://www.engineeringtoolbox.com/stoichiometric-combustion-d_399.html

All that heat remains inside your ideal combustion chamber (adiabatic process) and increases P and T, which does the mechanical work during the following stroke.

For your 2010 model, these are the values for one cylinder:

http://en.wikipedia.org/wiki/Kawasaki_Ninja_250R

Bore and Stroke: 62.0 mm × 41.2 mm
Compression Ratio: 11.6:1

The displacement volume (independent from the dead space at TDC) = Area of cylinder (bore) x stroke = (6.2 x 6.2 x Pi x 4.12) / 4 = 124.39 cm^3

Volume of combustion chamber at TDC = 124.39 / 11.6 = 10.72 cm^3

the head is about 10cc as Hernan has stated here. this was confirmed to me by millennium.

Isn't part of the purpose of the question to be able to calculate ΔT from your equations based on the ideal process the engine is going through at that point?

We can't just do your work for you.

I won't tell him anymore

Construct p-v and T-s diagrams for your vehicle's engine, assuming an Otto cycle.

If you do not own a vehicle, then use a vehicle you regularly ride in/on. And if the engine isn't gasoline (spark-ignition), then use some other engine that is.

Research as much information about your engine as possible. Make reasonable assumptions otherwise.

Present these two diagrams (and all calculations) on a piece of paper. Provide details about your engine and vehicle.

Due Friday, April 4, in class.

That's my actual assignment. The temperatures are going to be all assumptions. In fact, my professor WANTS assumptions. He doesn't want accuracy. He wants us to approach this project with the correct method. I've never touched an engine in my life, so I have absolutely no idea where to start with the assumptions. That is the reason why I asked this community.

The last project I did, which was due yesterday, was calculating the efficiency of my refrigerator. I have not taken a heat transfer class before, so I had to assume or ballpark the Qin/Qout. I took water, calculated deltaT and the time it took. This is probably super wrong, but as I mentioned, he did not care for accuracy. Rather how we approach the problem and how much work we put in to do it.

So, yea, I can assume that the temperature max is the temperature at which gasoline combusts, which I have found on Google to be 530K. It just doesn't sound right to me because he did an example where the Tmax was 3400 degrees Rankine.

I have no idea what EES and CFD is. This is a very basic thermodynamics course.

Good luck!

For me, heat transfer was a much easier course (I remember getting a 3.7 or 3.8, but it was long ago). Thermodynamics sucked.

I like heat transfer way more than I liked thermo. CFD is computational fluid dynamics. Basically it's a fancy way of saying that you model something on the computer and the software does computing for the fluid behavior for as many data points as you care to wait for.

EES is a basic program. It stands for Engineering Equation Solver. It has thermo properties and is able to solve a gigantic number of equations and variables in an iterative manner. Meaning if you can get your hw problem into a set of related equations, it will spit out answers, even if you have variables that are all dependent upon each other. Ask your prof if your school has a license to distribute EES to all the students. It's a very useful program for heat transfer and fluids and any clas where you have a lot of equations and variables and don't want to do the algebra. It also has tons of properties that you would find in the back of your thermo or fluids or heat transfer book.

Can you go ask your professor during his/her office hours for help on the method? Honestly I'm fuzzy on this because I've not done any work with engine cycles since sophomore year. I definitely remember being able to calculate T_max based on the equations and the diagrams though.

is there a language setting on this site? This thread doesn't seem to be in English

Looking at my profs notes for his current class, he have them a T_min of 540R and a T_max of 2400R for the example problem of an ideal Otto cycle. Maybe just pull that out of your butt and call it a feasible assumption?

Idle is about 350 when I go full throttle 1000~1200 is normal
Nitrous sends it close to 1400. If it goes over 1500 it melts plug tips.

Eric, this is exhaust temps in Farenheit correct? This might be the closest thing we have to actual numbers for T_max for the purpose of this question.

Yes Fahrenheit. This is a static test with the nitrous. You can see the exhaust temp at idle. It will sit at 350-450 then with the tap of the button it jumps to 600+
https://www.youtube.com/watch?v=OxIZyXmn288&feature=youtube_gdata_player