Specific heat in for the Otto cycle

In summary, the conversation discusses the process of modeling the Otto cycle using ideal gas properties for a class project. The speaker shares their approach of finding the specific calorific value of petrol and using it to approximate the value of qin. They mention using Excel solver to optimize the process and explain that their initial approximation does not affect the final optimized value. However, they express concern about not fully understanding the process of introducing heat in the Otto cycle and ask for alternative approaches to the problem.
  • #1
dinoclaro
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Thread moved from the technical forums to the schoolwork forums
A class project requires us to model the Otto cycle using ideal gas properties. We are not given the value for qin (specific heat in) and are told to make an intelligent approximation. My approach to this has been to find the calorific value of petrol, multiplying this by the density of petrol in which I then get the specific calorific value. I then proceed to multiply this by the volume of fuel in the cylinder (Volume at BDC divided by the air to fuel ratio). At the end of this process I get a value of around 980.35 J and cannot think of any way of converting this to specific heat as dividing by the mass obviously just returns the initial calorific value.

We are required to optimize the process using excel solver where the compression ratio and qin are the variables. Therefore this initial approximation has no bearing on the final optimized value (qin = 400Kj/Kg) . Although we are required to give an explanation of our initial value.

I fear that I am not understanding the Otto cycle process of where heat is introduced. Is there another way I should approach this problem?
 
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  • #2

FAQ: Specific heat in for the Otto cycle

1. What is specific heat in the context of the Otto cycle?

Specific heat is a thermodynamic property that measures the amount of heat required to raise the temperature of a unit mass of a substance by one degree. In the Otto cycle, specific heat is used to calculate the amount of heat absorbed or released during the compression and expansion processes.

2. How is specific heat related to the efficiency of the Otto cycle?

The specific heat of the working fluid in an Otto cycle directly affects the efficiency of the cycle. A higher specific heat means that the working fluid can absorb more heat during the combustion process, leading to a higher efficiency. Conversely, a lower specific heat results in lower efficiency.

3. How do you calculate specific heat in the Otto cycle?

The specific heat in an Otto cycle is calculated using the specific heat ratio, also known as the adiabatic index or gamma. This is a dimensionless quantity that represents the ratio of the specific heats at constant pressure and constant volume. The specific heat can be calculated using the formula: specific heat = (specific heat ratio / (specific heat ratio - 1)).

4. What factors can affect the specific heat in the Otto cycle?

The specific heat in the Otto cycle can be affected by the type of working fluid used, the temperature and pressure conditions, and the composition of the fuel-air mixture. Additionally, the specific heat can also be influenced by any heat transfer or energy losses within the system.

5. How can the specific heat in the Otto cycle be optimized?

To optimize the specific heat in the Otto cycle, engineers can make design choices such as selecting a working fluid with a higher specific heat ratio, controlling the temperature and pressure conditions, and minimizing heat transfer and energy losses within the system. Additionally, using more efficient combustion processes and fuel-air mixtures can also improve the specific heat and overall efficiency of the cycle.

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