diesel cycle - a four-stroke cycle in which combustion takes place at constant pressure and heat is rejected at constant volume

The Diesel cycle is a combustion process of a reciprocating internal combustion engine. In it, fuel is ignited by heat generated during the compression of air in the combustion chamber, into which fuel is then injected. This is in contrast to igniting the fuel-air mixture with a spark plug as in the Otto cycle (four-stroke/petrol) engine. Diesel engines are used in aircraft, automobiles, power generation, diesel–electric locomotives, and both surface ships and submarines.

The Diesel cycle is assumed to have constant pressure during the initial part of the combustion phase (
V
2
{\displaystyle V_{2}} to
V
3
{\displaystyle V_{3}} in the diagram, below). This is an idealized mathematical model: real physical diesels do have an increase in pressure during this period, but it is less pronounced than in the Otto cycle. In contrast, the idealized Otto cycle of a gasoline engine approximates a constant volume process during that phase. The Diesel engine is a heat engine: it converts heat into work. During the bottom isentropic processes (blue), energy is transferred into the system in the form of work
W
i
n
{\displaystyle W_{in}}, but by definition (isentropic) no energy is transferred into or out of the system in the form of heat. During the constant pressure (red, isobaric) process, energy enters the system as heat
Q
i
n
{\displaystyle Q_{in}}. During the top isentropic processes (yellow), energy is transferred out of the system in the form of
W
o
u
t
{\displaystyle W_{out}}, but by definition (isentropic) no energy is transferred into or out of the system in the form of heat. During the constant volume (green, isochoric) process, some of the energy flows out of the system as heat through the right depressurizing process
Q
o
u
t
{\displaystyle Q_{out}}. The work that leaves the system is equal to the work that enters the system plus the difference between the heat added to the system and the heat that leaves the system; in other words, net gain of work is equal to the difference between the heat added to the system and the heat that leaves the system.

1. Diesel cycle L. Rajitha Lakshan Karunarathne MES_2020_016 Lecturer - Mr. Inosh Weerakoon Assignment 01 - Applied Thermodynamics Constant Pressure Heat Addition Cycle

2. CONTENT 02 What is Diesel Cycle? Diesel Cycle Analysis. How Diesel Cycle Implemented in 4 Stroke Diesel Engine? Thermal Efficiency Diesel Cycle Application, Impacts of Diesel Emissions, Pros and Cons.

3. 01.What is Diesel Cycle? Invented by Rudolph Diesel in 1893. Diesel is used as fuel The diesel engines are working on this principle. Known as constant pressure cycle. Has high thermal efficiency and compression ratio. The ideal diesel cycle consists of four processes. 03

4. 02. Diesel Cycle Analysis. Processes The 4 processes are as follows 1. Isentropic (reversible adiabatic) Compression 2. Constant pressure heat addition 3. Isentropic Expansion 4. Constant volume heat rejection. 04

5. 05

6. Process 1-2:-Isentropic compression As process 1-2 is isentropic therefore heat transfer in this process is zero. Q 1−2 = 0 The change in internal energy for this process is given by, du 1−2 = C v (T 2 −T 1 ) By using the first law of thermodynamics, Q 1−2 =du 1−2 +W 1−2 0 = C V (T 2 −T 1 )+W 1−2 ∴W 1−2 = C v (T 1 −T 2 ) 06

7. Process 2-3:- Constant pressure heat addition The rate of heat transfer is equal to the change in enthalpy, Q 2−3 =C p (T 3 −T 2 ) The change in internal energy for the process 2-3 is given by, du 2−3 =C v (T 3 −T 2 ) Now by using first law of thermodynamics for the process 2-3, Q 2−3 = du 2−3 +W 2−3 C p (T 3 −T 2 )=C V (T 3 −T 2 )+W 2−3 W 2−3 = (C P −C V )(T 3 −T 2 ) Or the work done is also given by, W 2−3 = P 2 (V 3 −V 2 ) 07

8. Process 3-4:- Isentropic expansion As the process 3-4 is isentropic process. Therefore, Q 3−4 =0 The change in internal energy for this process is given by, du 3−4 =C V (T 4 −T 3 ) Now by using the first law of thermodynamics, Q 3−4 = du 3−4 +W 3−4 0 = C V (T 4 −T 3 )+W 3−4 ∴W 3−4 = C v (T 3 −T 4 ) 08

9. Process 4-1:- Constant volume heat rejection No work done is done or gained by the process. ∴W 4−1 =0 The change in internal energy, du 4−1 =C V (T 1 −T 4 ) The first law of thermodynamics for the process 4-1 can be written as Q 4−1 =du 4−1 +W 4−1 Q 4−1 = C v (T 1 −T 4 )+0 Q 4−1 = C v (T 1 −T 4 ) 09

10. 03. How Diesel Cycle Implemented in 4 Stroke Diesel Engine? Diesel engine have 2 extra processes. Suction process Exhaust process. Diesel is used as fuel. Have overall 6 Processes. 10

11. 0-1: Suction process 1-2: Isentropic compression process 2-3: Constant volume heat addition 3-4: Isentropic Expansion 4-1: Constant volume heat rejection 1-0: Exhaust process 11

12. 0-1: Suction process 1-2: Isentropic compression process 2-3: Constant volume heat addition 3-4: Isentropic Expansion 4-1: Constant volume heat rejection 1-0: Exhaust process 12

13. Diesel cycle work done: The Net work done from the diesel cycle is given by, W Net = Q Net W Net = Q 2−3 +Q 4−1 W Net = C P (T 3 −T 2 )+C V (T 1 −T 4 ) 04. Thermal Efficiency. 13

14. Diesel cycle efficiency derivation: The thermal efficiency of the diesel cycle is the ratio of net work to the heat supplied. For diesel cycle, η= W Net /Q 2−3 η= [C P (T 3 −T 2 )+C V (T 1 −T 4 )]/C P (T 3 −T 2 ) η= 1+ C V (T 1 −T 4 )/C p (T 3 −T 2 ) – Equation-1]     14

15. For isentropic process 1-2, the relation between T1 and T2 is given by, – Equation-2]         15

16. For the process 2-3, the relation between temperature T2 and T3 is given by, Putting the value of T1 from equation 1] – Equation-3]         16

17. For isentropic process 3-4, the relation between temperature T3 and T4 is given by, Putting the value of T3 from equation 3] – Equation-4] )                 17

18. Put the value of T2, T3 and T4 in equation 1], This is the equation for the thermal efficiency of diesel cycle         18  

19. Mean Effective Pressure – MEP Describe the performance of reciprocating piston engines. MEP of an atmospheric diesel engine can range from 7 to 9 bar . 19

20. 05. Diesel Cycle Applications, Impacts of Diesel Emissions, Pros and Cons. Applications Used in two-stroke and four-stroke diesel engine. Diesel generators Locomotives Farming equipment In construction equipment In cargo and cruise ships In buses and trucks 20

21. Impacts of Diesel Emissions Human Health Heart and lung disease Environment Production of ground-level ozone Acid rain Global Climate Air and water quality, weather patterns, sea levels, ecosystems, and agriculture. 21

22. Advantages of Diesel engines H as the highest effective Can combust a huge variety of fuel Low fuel costs. It has a high energy density Good lubrication properties Low risk of catching fire Diesel engines have very good exhaust-emission behavior. 22

23. Disadvantages of Diesel engines Cars with Diesel engine usually cost more than a standard vehicle Maintenance of diesel engine and repair cost more. The new diesel fuel doesn’t have the same lubricating qualities. D ifficult to start a diesel engine in cold weather. Diesel engines much noise 23

24. Conclusion Discussed the process of the Diesel Cycle with the P-V and T-S diagrams and also have derived the equation for the Efficiency and Discussed the process of the Diesel Engine. Also considered about Diesel Cycle Applications, Impacts of Diesel Emissions, Pros and Cons. 24

25. Any Questions ? 25

26. References https://studentlesson.com/working-principles-advantages-and-disadvantages-of-diesel-engine-studentlesson/#Working_principles_of_diesel_engine https://themechanicalengineering.com/diesel-cycle/#Diesel_Cycle_PV_and_TS_Diagram https://www.mechanicalbooster.com/2017/10/diesel-cycle.html#How_Diesel_Cycle_Implemented_in_4_Stroke_Diesel_Engine https://mechcontent.com/diesel-cycle/#Diesel_cycle_PV_and_TS_diagram https://www.epa.gov/dera/learn-about-impacts-diesel-exhaust-and-diesel-emissions-reduction-act-dera 26