# A gasoline engine has a piston/cylinder with 0.1 kg air at ## Problem 156HP Chapter 3

Fundamentals of Thermodynamcs | 8th Edition

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Problem 156HP

A gasoline engine has a piston/cylinder with 0.1 kg air at 4 MPa, 1527°C after combustion, and this is expanded in a polytropic process with n = 1.5 to a volume 10 times larger. Find the expansion work and heat transfer using the heat capacity value in Table A.5.

TABLE A.5

Properties of Various Ideal Gases at 25°C, 100 kPa*(SI Units)

 Gas ChemicalFormula Molecular Mass(kg/kmol) R(kJ/kg-K) ρ (kg/m3) Cp0(kJ/kg-K) Cv0(kJ/kg-K) Steam H2O 18.015 0.4615 0.0231 1.872 1.410 1.327 Acetylene C2H2 26.038 0.3193 1.05 1.699 1.380 1.231 Air — 28.97 0.287 1.169 1.004 0.717 1.400 Ammonia NH3 17.031 0.4882 0.694 2.130 1.642 1.297 Argon Ar 39.948 0.2081 1.613 0.520 0.312 1.667 Butane C4H10 58.124 0.1430 2.407 1.716 1.573 1.091 Carton dioxide CO2 44.01 0.1889 1.775 0.842 0.653 1.289 Carton monoxide CO 28.01 0.2968 1.13 1.041 0.744 1.399 Ethane C2H6 30.07 0.2765 1.222 1.766
Step-by-Step Solution:

Solution 156HP

Step 1 of 3</p>

We are required to calculate the expansion work and heat transfer during the given process.

Step 2 of 3</p>

The mass of air in the cylinder is kg

The given process is polytropic and the value of is 1.5.

The initial specific volume is The final specific volume is The initial pressure is MPa kPa

Let the final pressure be .

In a polytropic process, constant

Thus,     kPa

The work done in a polytropic process is,  , where and are initial and final temperatures. C = 1800 K

From the ideal gas equation, , and Therefore,   K

Substitute and values in  J [R for air is (8.314/ air molar mass= 28.97 g/mol)] kJ

Therefore, the work done is 70.6 kJ.

Step 3 of 3

##### ISBN: 9781118131992

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