Language
Country/Area
No result found
Supercharger and Miller Cycle: How is energy bursting out in the engine?
In modern engineering, the Miller cycle is regarded as an innovative thermodynamic cycle, especially in the design of internal combustion engines. First patented by American engineer Ralph Miller in 1957, this engine technology combines the advantages of a supercharger to improve engine performance and achieve higher fuel efficiency.
Traditional internal combustion engines mostly use four strokes, including two high-power strokes: compression stroke and power stroke. In the Miller cycle, the intake valve is open for a long time, causing the compression stroke to be divided into two stages. During this process, part of the fuel mixture entering the cylinder is pushed back into the intake port, which usually results in a loss of power, but the Miller cycle compensates for this loss with the assistance of a supercharger.
The Miller cycle is characterized by its "fifth stroke", which is not common in traditional engine designs.
The design of the compression ratio and expansion ratio of the Miller cycle engine makes the compression of the fuel mixture more efficient. When the intake valve is closed, the piston performs real compression, which allows the engine to operate at a lower temperature, thus improving overall thermal efficiency.
Operation principle of Miller cycle
In the Miller cycle, the operation of the supercharger is crucial. This device can still produce sufficient boost at relatively low speeds, allowing the engine to maintain good performance under various operating conditions. In contrast, operating efficiency can be further improved through the combination of a supercharger and a turbocharger, but this also comes from higher technical challenges.
A notable feature of the Miller cycle is that when the piston starts to compress the fuel, the intake valve is still open, so that during the initial part of the compression stroke, the piston pushes part of the fuel mixture back into the intake manifold again. Tube. This may seem like a loss, but it's more than compensated for by the power of supercharging.
Control of inflation temperature
One of the advantages of the Miller cycle is that it can reduce the temperature of the inlet gas. Through the cooling effect of the supercharger, this operation not only improves the power performance of the engine, but also increases the density of the air while reducing pressure. The intention behind this design is to improve combustion efficiency and reduce nitrogen oxide emissions, which is particularly important in large diesel engines on ships and power plants.
Reducing the final charge temperature continuously improves the overall efficiency of the engine, and can further advance the ignition timing and break through the normal knock limit.
Compression ratio and energy efficiency
The Miller cycle greatly increases energy efficiency due to its effective combination of compression and expansion ratios. Since during the expansion stroke, the gas can be expanded almost to atmospheric pressure, this creates good conditions for the engine's energy recovery. However, these designs also come with some trade-offs, such as the loss of a supercharger and fluctuations in performance.
Supercharger Challenge
Although using a positive displacement supercharger can improve engine performance, it will also cause additional energy loss, accounting for about 15 to 20% of the generated power. In addition, the turbocharger may experience lag at low rpm, which requires the engine to rely on the Miller cycle to continue operating at lower rpm to make up for the performance gap.
Summary
In current automobile design, the Miller cycle is undoubtedly a major feature that improves combustion efficiency. Whether it is a general consumer car or a high-performance racing car, this engine design shows its excellent advantages and practicality. With the development of technology, the balance between supercharging technology and engine cycle will become increasingly critical in the future. So, how can future engine designs find the best balance between performance and environmental protection?
