Diesel Cycle vs Otto Cycle 

 we will discuss the difference between the Diesel cycle and vs Otto Cycle. Both these cycles are air standard cycles of automobile engines. Otto cycle is used for petrol or spark ignition engines while the diesel cycle is used for diesel or compression ignition engines. The main difference between the Otto cycle and the Diesel cycle is that in the Otto cycle heat addition takes place at constant volume and in diesel cycle heat addition takes place at constant pressure. This is the major difference between the Otto cycle and diesel cycle. There are many other differences which are described below. S.No. Otto Cycle Diesel Cycle 1. Otto cycle is given by the Nicolas Otto in 1876. It was given by Dr. Rudolph Diesel in 1897. 2. It is ideal cycle for petrol engine. It is ideal cycle for diesel engine. 3. Otto cycle has higher thermal efficiency. It has lower thermal efficiency. 4. This cycle has comparatively low compression ratio. It compresses the mixture up to 11:1 ratio. Diesel cycle has high compression ratio. It compresses the mixture up to 22.1 ratios. 5. Otto cycle engine used spark plunge to ignite the air fuel mixture. Fuel automatically ignites due to high temperature of compressed gas. 6. Heat addition takes place at constant volume. Heat addition takes place at constant pressure. 7. Air fuel mixture drawn into the cylinder during intake stroke. Once air is drawn into intake stroke. Fuel is injected after end or compression stroke by an injector. Otto Cycle The Otto Cycle, describes how heat engines turn gasoline into motion. Like other thermodynamic cycles, this cycle turns chemical energy into thermal energy and then into motion. The Otto cycle describes how internal combustion engines (that use gasoline) work, like automobiles and lawn mowers. Application The Otto Cycle provides the energy for most transportation and was essential for the modern world. Specifically, the vast majority of automobiles seen on the road today use the Otto Cycle to convert gasoline into motion. Any machine (the list[1] would go on and on) that uses gasoline will be divided into two categories of engines as seen below. Types of engines that use the Otto Cycle Figure 1. A two stroke engine[2] Figure 2. A four stroke engine[3] The PV diagram (pressure-volume diagram) of the ideal Otto cycle is show above fig. This diagram models how the changes in pressure and volume of the working fluid (gasoline and air fuel) change due to the combustion of hydrocarbons which powers the movements of a piston, creating heat, to provide motion for a vehicle. There are expansion (increased volume chamber) piston motions—caused when the thermal energy is released from combustion— inducing work being done by the gas and on the piston. In contrast, when the piston does work on the gas, the engine chamber is being compressed (decreasing in volume). It is important to note that Figure, depicts an ideal process for any engine using the Otto cycle. It describes the basic working steps in a gasoline engine. The slight modification which depicts a more realistic situation of the Otto Cycle's PV diagram for a two stroke and four stroke engine is explained on their respective pages. The work done by the engine can be calculated by solving the area of the closed cycle. The following describes what occurs during each step on the PV diagram, in which the combustion of the working fluid—gasoline and air (oxygen), changes the motion in the piston: Green line: Referred to as the intake phase, the piston is drawn down to the bottom to allow the volume in the chamber to increase so it can "intake" a fuel-air mixture. In terms of thermodynamics, this is referred to as an isobaric process. Process 1 to 2: During this phase the piston will be drawn up, so it can compress the fuel-air mixture that entered the chamber. The compression causes the mixture to increase slightly in pressure and temperature—however, no heat is exchanged. In terms of thermodynamics, this is referred to as an adiabatic process. When the cycle reaches point 2, that is when the fuel is met by the spark plug to be ignited. Process 2 to 3: This is where combustion occurs due to the ignition of fuel by the spark plug. The combustion of the gas is complete at point 3, which results in a highly pressurized chamber that has a lot of heat (thermal energy). In terms of thermodynamics, this is referred to as an isochoric process. Process 3 to 4: The thermal energy in the chamber as a result of combustion is used to do work on the piston—which pushes the piston down—increasing the volume of the chamber. This is also known as the power stoke because it is when the thermal energy is turned into motion to power the machine or vehicle. Purple line (Process 4 to 1 and exhaust phase): From process 4 to 1, all waste heat is expelled from the engine chamber. As the heat leaves the gas, the molecules lose kinetic energy causing the decrease in pressure.[6] Then the exhaust phase occurs when the remaining mixture in the chamber is compressed by the piston to be "exhausted" out, without changing the pressure.