Part b) determine the thermal efficiency Part c) determine the mean effective pr

Question

Part b) determine the thermal efficiency Part c) determine the mean effective pressure in kPa
*note the problem says use ideal gas model not perfect gas so you can't use the equation 1-(1/r^k-1) to find thermal efficiency I've already tried that and it didn't accept my answer. e previous | 4 of 4 return to assig An air standard Otto cycle is has a compression ratio of 9. At the beginning of the compression, pressure is 95 kPa and t , and the maxihum temperature in the cycle is 750 C. Use the IG model for air. Assume mass of air as 0 005 kg emperature is 30 °C. Heat addition to the air is 1kJ/kg Part A Determine the net work Express your answer to three significant figures and include the appropriate units. 146 /kJ Submit My Answers Give Up Incorrect: One attempt remaining; Try Again Part B Determine thermal efficiency Express your answer to the nearest tenth.

Explanation / Answer

An air standard otto cycle is considered that means the air is considered as ideal or perfect gas which are both same.

Compression ratio is given i.e rk=9

As we know compression ratio is the ratio of intial volume (before compression )and final volume (end of compression .

As we know the efficiency in air standard cycle is given by:   1-(1rk)1.4-1

Thus efficiency of otto cycle becomes      =1-(1/9)0.4=0.584

And efficiency=work/heat supplied

Thus, work done =.584*1kj/kg*.005kg=2.924*10-3 kJ

Mean effective pressure =work done/swept volume

Where swept volume is the difference between volumes at the starting of compression and at the end of compression in the internal combustion engine.i.e. V1-V2

To calculate V1 ,we use ideal gas equation PV=mRT

Thus, V1=mRT1/P1

M=mass=.005kg

R=characterstic gas constant=0.287kJ/kgK

T1=temperature at the starting of compression which is given in question=30 celcius=(30+273)K=303 K

Here degree Celsius is converted into Kelvin as all units are in Kelvin

Therefore, V1=0.005*0.287*303/95=0.00457 m3

And V1/V2 is given as the compression ratio=9

Therefore,V2=V1/9=0.0005085 m3

Hence swept volume=V1-V2=0.00457-0.0005085=0.0040615 m3

Now we can easily calculate mean effective pressure=work done/swept volume=

2.924*10-3 kJ/0.0040615 m3   =0.7199 kPa

Related Questions

Navigate

• Browse (All)
• Browse P
• Subjects

---