What are the types of processes that occur in the Otto cycle?
The four-stroke Otto cycle is made up of the following four internally reversible processes: 1–2, isentropic compression; 2–3, constant-volume heat addition; 3–4, isentropic expansion; and 4–1, constant-volume heat rejection.
The ideal Otto cycle is an example of an isochoric process when it is assumed that the burning of the gasoline-air mixture in an internal combustion engine car is instantaneous. There is an increase in the temperature and the pressure of the gas inside the cylinder while the volume remains the same.
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.
In such a case, a better approach for modelling the situation will be to assume heat addition initially at constant volume and then at constant pressure. That is why dual combustion cycle is used.
In the Otto cycle, there is no heat transfer during the process 1–2 and 3–4 as they are isentropic processes.
Explanation: The Otto cycle is air standard cycle and is used in SI engine. Explanation: This is the functioning of a four-stroke internal combustion engine.
An isobaric process is a process occurring at constant pressure. The first law of thermodynamic equation for the isobaric process remains the same as the pressure remains constant and because of the volume change, the system does work.
1) Isochoric process is a chemical process that takes place in a thermodynamic system under a constant volume. 1) An isobaric process is a chemical process that takes place in a thermodynamic system under constant pressure. 2) There is no change in volume ΔV=0.
An example of the isobaric process includes the boiling of water to steam or the freezing of water to ice. In the process, a gas either expands or contracts to maintain constant pressure and hence the net amount of work is done by the system or on the system.
The Otto engine operates with a mixture compressed in a cylinder by a piston. Shortly before the piston reaches the top the mixture is ignited with a spark, and the flame propagates at a normal velocity into the unburned mixture, increasing the pressure and moving the…
What is Otto cycle also called?
constant temperature cycle and pressure cycle.
The air standard Otto cycle is modeled as a closed system with a fixed air/fuel mass, and uses the following process assumptions: 1-2 Compression which is reversible and adiabatic. 2-3 Heat addition from fuel. 3-4 Expansion which is reversible and adiabatic.
Diesel cycle is used in the compression ignition engine.
6 Diesel Cycle
An idealized Diesel engine cycle is shown in Figure 3.12. This cycle can operate with a higher compression ratio than the Otto cycle because only air is compressed and there is no risk of auto-ignition of the fuel.
However, higher compression ratios will make gasoline engines subject to engine knocking, caused by the autoignition of an unburned mixture, if lower octane-rated fuel is used. The unburned mixture may auto-ignite by detonating from pressure and heat alone rather than igniting the spark plug at exactly the right time.
The Otto Cycle involves four engine strokes. A stroke is defined as a process in which the cylinder's piston moves up to the top of the engine or down to the bottom of the engine.
13.7.1 Mean Effective Pressure (MEP; Otto Cycle)
At the beginning of the compression stroke, the temperature is 300K and pressure is 100 kPa. Thermal energy q is supplied at 1840 kJ/kg.
Compression stroke: The valves are closed and the piston moves upwards, reducing the volume available and thus increasing the pressure. Near the end of this stroke, the combustion starts either triggered by a spark (in spark ignition engines) or self-induced by the pressure levels (as in compression ignition engines).
What is Isochoric Process? A thermodynamic process taking place at constant volume is known as the isochoric process. It is also sometimes called as an isometric process or constant-volume process.
An isochoric process is one where the volume stays constant, and the temperature and pressure change relative to each other. An isothermal process is one where the temperature stays constant, and the pressure and volume change relative to each other.
Is isobaric compression possible?
Specific heat capacity
An isobaric process is shown on a P–V diagram as a straight horizontal line, connecting the initial and final thermostatic states. If the process moves towards the right, then it is an expansion. If the process moves towards the left, then it is a compression.
The adiabatic process has been important for thermodynamics since its early days. It was important in the work of Joule because it provided a way of nearly directly relating quantities of heat and work. Energy can enter or leave a thermodynamic system enclosed by walls that prevent mass transfer only as heat or work.
The process in which there is no exchange of heat between the system an the surrounding is known as adiabatic process. The process during which the temperature of gas remains constant is known as isothermal process.
An isochoric process, also called an isometric process or an isovolumetric process, is a process during which volume remains constant. The name is derived from the Greek isos, "equal", and khora, "place."
A refrigerator works isothermally. A set of changes take place in the mechanism of a refrigerator but the temperature inside remains constant. Here, the heat energy is removed and transmitted to the surrounding environment. Another example of an isothermal process is the heat pump.
Detailed Solution. Since volume of pressure cooker is constant hence it is an Isochoric process.
The Otto cycle engine employs a spark to ignite a mixture of air and, traditionally, gasoline2 compressed by the piston within the engine cylinder. This spark ignition causes an explosive release of heat energy that increases the gas pressure in the cylinder, forcing the piston outwards as the gas tries to expand.
The Otto cycle is a cycle of engine operation which requires four strokes of the piston: for induction, compression, ignition, and exhaust. The fuel and air mixture is compressed before combustion is started by an electrical spark or other means. Named after German engineer Nikolaus Otto.
The main difference between Otto and Diesel cycle is that The otto cycle explosion process takes place at a constant volume process and the Diesel cycle explosion process takes place at a constant pressure process.
For the Otto cycle engine, the expansion ratio is equal to the compression ratio, whereas for the Miller cycle engine, one can define a 'Miller cycle ratio', , expressing the relative difference between expansion ratio and compression ratio: ε = r e r c = V c / V a V b / V a = V c V b where is the Miller cycle ...
Is the Otto cycle a polytropic process?
The Otto cycle includes four branches: two isochors and two reversible adiabatic processes. The adiabatic processes may be replaced by two polytropic processes to account for the deviations from the ideal branches.
The first process in the Otto cycle is an adiabatic compression, which decreases the volu me and increases the pressure. No heat flows into or out of the system during this process but work is done by the surroundings on the system.
In a closed-cycle OTEC system, warm seawater vaporizes a working fluid such as ammonia flowing through an evaporator. The vapor expands at moderate pressures and turns a turbine coupled to a generator that produces electricity.
Solved Problem 3.7 - An ideal air-standard Otto cycle engine has a compression ratio of 8. At the beginning of the compression process, the working fluid is at 100 kPa, 27°C (300 K), and 800 kJ/kg heat is supplied during the constant volume heat addition process.
What is the overall best compression format? It depends on user's need, with compression ratio being only one factor of the equation. ZPAQ and ARC are the best compressors, but 7Z and RAR formats has a clear advantage in terms of decompression speed, faster than for any other tested format.
Increase in compression ratio increases the pressure and temperature of the gases at the end of the compression stroke. This decreases the ignition lag of the end gas and thereby increasing the tendency fordetonation.
A higher compression ratio (CR) is beneficial for engines. That's because the higher ratio allows for an engine to extract more energy from the combustion process due to better thermal efficiency. Higher compression ratios allow the same combustion temperatures to be achieved with less fuel.
In Diesel cycle, process 1-2 is isentropic compression process. It gives, Hence, the compression ratio of an ideal Diesel-cycle is 24.3, which is much higher than the compression ratio of an ideal Otto-cycle, which is 6.7.
Hence, for constant values of compression ratio, both the efficiencies have same values. But in practice, Brayton cycles are used for larger values of compression ratios and Otto cycle is used for small values of compression ratio. Hence, the formula of efficiency may be same but their applications are different.
Diesel Cycles have four stages: compression, combustion, expansion, and cooling.
How many stages are there in the Otto cycle?
Otto Cycles have four stages: expansion, cooling, compression, and combustion.
The four-stroke cycle is often called the Otto cycle, after the German Nikolaus…
The most significant difference between the ideal Otto cycle and the ideal Diesel cycle is the method of igniting the fuel-air mixture.
In the diesel engine, only air is initially introduced into the combustion chamber. The air is then compressed with a compression ratio typically between 15:1 and 23:1. This high compression causes the temperature of the air to rise.
Solved Problem 3.6 - An ideal air-standard Diesel cycle engine has a compression ratio of 18 and a cutoff ratio of 2. At the beginning of the compression process, the working fluid is at 100 kPa, 27°C (300 K).
Otto cycle The Otto Cycle is named after Nikolaus Otto (1832–1891, German) who is credited as the first creator of a petroleum fuel based internal combustion engine operating under a four stroke cycle.
The Otto engine operates with a mixture compressed in a cylinder by a piston. Shortly before the piston reaches the top the mixture is ignited with a spark, and the flame propagates at a normal velocity into the unburned mixture, increasing the pressure and moving the…
Although for a given compression ratio the Otto cycle has higher efficiency, because the Diesel engine can be operated to higher compression ratio, the engine can actually have higher efficiency than an Otto cycle when both are operated at compression ratios that might be achieved in practice.
While the original Otto cycle engine used gasoline as a fuel source, diesel engines use the same 4-cycle operation through mixing a fuel/air mixture, fuel compression, downward combustion and exhaust. The difference being a diesel fuel/air mixture is ignited by compression instead of a spark.
Thus, the Otto cycle is the most efficient and the Diesel cycle is the least efficient of the three cycles.
Which cycle is more efficient for the same compression ratio?
For same compression ratio, the efficiency of an Otto cycle is higher than that of the diesel cycle.
Diesel cycle is used in the compression ignition engine.