Specific heat capacity

[Azmio]

I got confused a bit over the heat capacity of various gases. In my Bosch handbook, CO2 has cp of 0.82 and cv of 0.63. Nitrogen on the other hand has cp of 1.04 and cv of 0.74. From the property table it is clear that nitrogen has higher number if compared to CO2 but i am wondering on why many SAE papers keep on mentioning that CO2 has higher heat capacity. Is it because of the total charge has increased with the addition of EGR or the CO2 itself has higher specific heat capacity?

 

[crysta1c1ear]

http://www.engineeringtoolbox.com/carbon-dioxide-d_974.html

http://www.engineeringtoolbox.com/nitrogen-d_977.html

Specific heat capacity
- cp -
(kJ/kgK)


At 300K
Carbon Dioxide 0.846
Nitrogen 1.040

At 1000K
Nitrogen 1.167
Carbon Dioxide 1.234

I guess the documents you are looking at saying CO2 has the higher heat capacity are referring to hot gasses,
or maybe they are calculating on a per molecule rather than per kilogram basis.

It looks like at low temperatures it is easier to heat carbon dioxide than nitrogen, as you are warming less molecules when you heat a kilogram of CO2. And then at higher temperatures it takes more energy, as you have to make the molecules bend too. Diatomic molecules like nitrogen N-N stay linear. CO2
can bend 0-C-O

O
|
C-O

 

[Azmio]

Crystal,

Thanks a lot buddy. If I may ask, at peak cylinder temperature just after TDC, should we use cp or cv?

 

[SomptingGuy]

It sounds to me like you should be asking Santa for a copy of Heywood this Christmas.

- Steve

 

[Azmio]

sompting

I used heywood textbook in my internal combustion engine course back in 95. I still have it and been referring to it from time to time.

I'm not sure whether heywood textbook answered my question as what I posted above. if you happen to see the answer in heywood, tell me which page to go to

 

[SomptingGuy]

I would say that chapter 5 is your best bet. In my copy, section 5.4 starts on page 169: " Cycle analysis with ideal gas working fluid with Cv and Cv constant".

(However, my favourite is chapter 4: "Properties of working fluids". Maybe I'm just sad?)

- Steve

 

[SomptingGuy]

Yikes, what a typo!. "Cv and Cp constant"

- Steve