1. AE 427 THERMODYNAMIC CYCLE SIMULATION Prof.Dr. Demir Bayka

3. DIESEL ENGINE Diesel engines have been used as prime movers for heavy duty vehicles. Due to their high efficiency and low pollutant formation characteristics, their application to lighter duty vehicles has drawn much attention in recent years. Research in this field is continuing to develop engines with better operational characteristics necessitated by the energy crisis and environmental legislation's.

4. The development of an engine for a particular application can be approached either directly by exploratory testing or indirectly by using a mathematical model to predict the engine behaviour. For experimental investigations, extensive testing of the prototype is necessary, besides, selecting the best design from such testings is a task of considerable magnitude.

5. On the other hand reduction in time and costs for the development and design of new engines can be achieved through simulation models that give a good representation of the engine system.

6. The principle on which a simulation of the engine working cycle is based is essentially a step-by-step integration of the First Law of Thermodynamics applied to the working gas This is an instantaneous account of the energy balance.

7. STATE OF THE MIXTURE AT THE BEGINNING OF THE CYCLE The diesel engine cycle consists of the following sequence of events: 1. A compression stroke to raise the cylinder charge to a temperature and pressure higher than the ignition point of the fuel.. 2. An expansion stroke during which the "heat released" by the combustion of injected fuel is converted into useful mechanical work. 3. An exhaust stroke to expel the burned gases from the cylinder. 4. An intake stroke to induct air alone into the cylinder.

8. The complete cycle will be analyzed starting from the compression stroke when the intake valve closes, while the piston is moving upward. So the intake valve closing will be selected as the beginning of the cycle.

9. State of Mixture at the Beginning of the Cycle The clearance volume of the reciprocating engine contains some of the products of combustion at the end of the exhaust stroke. The clearance gases have a high temperature and mix with the air inducted, the final temperature being the temperature of the mixture at the beginning of the compression process.

10. The amount and temperature of the clearance gases have an appreciable effect on the temperature of the mixture at the end of the induction stroke, and since this temperature and the entire cycle process determine the state of clearance gases it is necessary to make assumptions about the state of mixture at the beginning of the cycle.

11. PROCEDURE Assume Cylinder Gas Pressure, Cylinder Gas Temperature and The Residual Gas Fraction in the chamber at the beginning of the cycle.

12. The Residual Gas Fraction Residual gases initially are assumed to be the combustion products from the previous cycle, its composition being fixed at the beginning of the exhaust stroke where the dissociation is considered to be complete. So, composition of residual gasses, x p is determined from the calculation of equilibrium composition of combustion products.

13. The composition of the charge at the beginning of the cycle is determined from the relation x i = x pi x res + x air x ai............(1) x i = mole fraction of i th specie in the cylinder. x pi = mole fraction of ith specie in the residual gas alone. x res = residual gas mole fraction in the cylinder. x ai = mole fraction of ith specie in air alone (if any). x air = mole fraction of air in the cylinder.

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