A gasoline engine and a diesel engine differ significantly in two ways. First, the gasoline engine runs on a theoretical air standard cycle, often known as a “constant volume cycle,” which involves periodic combustion and work creation. When the piston is at top dead center (TDC) on its compression stroke, where pressure rises but the volume above the piston crown remains constant, combustion of the air/fuel charge is finished. To start a flame front, a high-tension spark from an electrical/electronic ignition system is transmitted to a spark plug. Combustion time is mostly determined by the speed at which the flame propagates, which is normally in the 20 to 40 second range.
The air/fuel ratio in today’s vehicle gasoline engines is “stoichiometric.” Simply described, it is the mass ratio (of air to combustible gas or vapor) at which complete combustion or chemical combination occurs. 14.5 oz
Second, unlike gasoline engines, diesel engines don’t have a stoichiometric air/fuel ratio. Because the air entering the cylinders is unthrottled, the air/fuel ratio in a diesel is extremely low at idle (minimum fuel delivery) (not restricted as it is on a typical gasoline engine). Because more fuel is injected to provide more power at higher loads/speeds, the diesel air/fuel ratio will run richer. As a result, at idle, the air/fuel ratio of a diesel engine can be as high as 90:1 or 100:1, with some engines running even leaner. The air/fuel ratio can decrease as low as 25:1 or 30:1 during full-load/high-speed operation. Furthermore, a diesel engine follows a theoretical “constant pressure cycle,” in which fuel is provided as the piston goes down the cylinder on its power stroke at a pace that keeps the cylinder pressure constant throughout the combustion process. The diesel is also reported to run on a heterogeneous charge of compressed air generated during the piston’s upward-moving compression stroke, which is backed up by a finely atomized spray of high-pressure liquid fuel injected just before the piston reaches TDC. The injected diesel fuel vaporizes due to the heat generated in the trapped air from the upward-moving piston compression stroke (hot high-pressure air only). The self-ignition capabilities of the air/fuel mixture initiate combustion to form a flame front within the combustion chamber after a short time (ignition) delay, where the air and injected fuel mix. As a result, any additional gasoline injected has no ignition delay and burns instantly. Peak cylinder pressures of 18002300 psi (12,41115,858 kPa) can be achieved with the greater compression ratio used in today’s high-speed, heavy-duty diesel engines.
(In actuality, no internal combustion engine, whether gasoline or diesel, uses either the constant pressure or constant volume combustion phases.) Each requires a little amount of crankshaft rotation to complete combustion, as well as a rise in cylinder pressure during the process. As a result, a dual cycle that falls somewhere between the Otto and Diesel curves would be a better representation of the theoretical curve for both gasoline and diesel IC engine cycles. Because IC engines do not run on ideal cycles and instead use real gas during combustion, they suffer from flow and pumping losses, as well as thermodynamic and mechanical losses owing to friction.)
Is Diesel cycle a constant pressure cycle?
Isentropic compression, isobaric heat addition, isentropic expansion, and isochoric heat rejection are the processes in the diesel cycle. As a result, an air standard diesel cycle consists of two adiabatic processes, one constant volume, and one constant pressure.
What is the engine also called as constant pressure cycle engine?
Explanation: The diesel cycle is known as a constant pressure cycle because the heat addition process occurs at a constant pressure, whereas the petrol cycle is known as a constant volume cycle because the heat addition occurs at a constant volume.
What is the difference between constant volume and constant pressure?
The heat of reaction is equal to the enthalpy change at constant pressure. The heat of reaction is equal to the change in internal energy at constant volume.
What is Diesel cycle process?
The Diesel cycle is a reciprocating internal combustion engine’s combustion process. The heat generated by the compression of air in the combustion chamber ignites the fuel, which is subsequently injected into the combustion chamber. This is in contrast to the Otto cycle (four-stroke/petrol) engine, which uses a spark plug to ignite the fuel-air mixture. Aircraft, vehicles, power generation, diesel-electric locomotives, and both surface and submarine ships employ diesel engines.
During the initial part of the combustion phase, the Diesel cycle is believed to have constant pressure (
What is the difference between Diesel cycle and Otto cycle?
For petrol or spark ignition engines, the Otto cycle is utilized, while for diesel or compression ignition engines, the diesel cycle is used. The major difference between the Otto and Diesel cycles is that in the Otto cycle, heat is added at a constant volume, but in the Diesel cycle, heat is added at a constant pressure.
Which cycle can be called as a constant volume cycle?
The constant volume heat addition cycle, often known as the Otto cycle, considers one special example of an internal combustion engine in which combustion occurs so quickly that the piston does not move during the process, and hence combustion is believed to occur at constant volume.