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The secret difference between the Miller cycle and the Atkinson cycle: Why is more than 20% of the power output converted?
In the engineering field of internal combustion engines, the Miller cycle is a thermodynamic cycle proposed and patented by American engineer Ralph Miller in 1957, marking a major change in internal combustion engine technology. This technology not only improves the operating efficiency of internal combustion engines, but also lays the foundation for environmentally friendly power systems.
The Miller cycle is designed to allow the engine to operate in a way that offsets the performance losses of the Atkinson cycle.
Basic principles of Miller cycle
Conventional piston internal combustion engines generally operate using four strokes, two of which are considered high-power strokes: the compression stroke and the power stroke. In the Miller cycle, the opening time of the intake valve is extended so that part of the mixed gas can be pushed out at the beginning of the compression stroke, forming the so-called "fifth stroke". While this design helps improve energy conversion efficiency, it also creates challenges because some of the gas is exhausted back into the intake manifold.
In the Miller cycle, this loss is compensated by the use of a supercharger, which improves the overall efficiency of the engine.
Charge Temperature and Compression Ratio
In the Miller cycle, low temperatures increase the density of the air, thereby increasing the engine's power without increasing the compression ratio of the cylinder and piston. When the charge temperature is lowered, the fuel mixture burns at a higher force, helping to reduce nitrogen oxide (NOx) emissions, especially in heavy-duty diesel engines.
In addition, the Miller cycle's superior expansion ratio compared to the compression ratio also allows more power to be extracted during the combustion process, increasing the overall efficiency of the engine. This shows that the potential applications of this technology in aviation and industrial transportation are very broad.
By increasing the effective compression ratio and expansion ratio, the Miller cycle achieves the goal of improving energy efficiency.
Benefits and Challenges of Superchargers and Turbochargers
In the Miller cycle, the supercharger usually brings about a power loss of about 15% to 20% to drive the supercharger to charge, which is its disadvantage. But in comparison, turbochargers can use exhaust gas more efficiently, reducing power dependence and pressure loss, especially when low-speed operation is not required.
Although turbochargers have performance delays, their potential for application in commercial engines cannot be underestimated as technology advances.
Advantages and applications of Miller cycle
The main advantage of the Miller cycle is that its expansion ratio is greater than the compression ratio, which makes it possible to more effectively reduce emissions during operation and further improve engine performance. This technology is particularly suitable for diesel engines used in ships and large power plants.
Although the Miller cycle has better power output than the Atkinson cycle, in practical applications it is still necessary to balance the relationship between efficiency and structural cost so as to make adjustments based on actual needs.In the context of pursuing sustainable development, how to effectively integrate these advanced technologies will be the key to promoting the advancement of internal combustion engine technology.
With the growing demand for environmentally friendly travel, internal combustion engine technology faces major challenges and opportunities. The further development and application of the Miller cycle may inject new impetus into future transportation. As technology advances, which powertrain do you think will become mainstream in the next market?
