Pulse System vs. Constant Pressure System in Turbochargers for Large Medium Speed Diesel Engines:
(a) Pulse System:
The pulse system, also known as the pulse converter system, is a specific type of turbocharging arrangement used in some large medium-speed diesel engines. It utilizes the pulsating nature of exhaust gas flow from each engine cylinder to optimize turbocharger performance. Here’s how it works:
- Exhaust Grouping: Unlike a constant pressure system where all exhaust pipes combine into a single large manifold, the pulse system groups exhaust pipes from a specific number of cylinders together.
- Pulse Wave Utilization: The exhaust piping for each group is designed to minimize interaction between the exhaust pulses from individual cylinders. This allows each pulse of high-velocity exhaust gas to reach the turbine inlet with minimal energy loss.
- Optimizing Turbine Response: By utilizing the individual high-pressure pulses from each cylinder group, the pulse system can improve the efficiency of energy transfer from the exhaust gas to the turbine. This allows for better responsiveness of the turbocharger, especially at lower engine speeds.
(b) Advantages of Pulse System over Constant Pressure System:
The pulse system offers several advantages compared to the more common constant pressure system for large medium-speed diesel engines:
- Improved Low-Speed Performance: The pulse system’s ability to utilize individual exhaust pulses is particularly beneficial at lower engine speeds. At these speeds, a constant pressure system might experience reduced efficiency due to lower exhaust gas flow. The pulse system’s focused use of high-pressure pulses helps maintain better turbocharger responsiveness and boost pressure at lower RPMs.
- Reduced Lag: Turbo lag refers to the delay between increased engine speed and the corresponding rise in boost pressure. The pulse system’s efficient utilization of exhaust pulses can help minimize turbo lag, leading to improved engine response and acceleration.
- Potential for Smaller Turbocharger: In some cases, the improved efficiency of the pulse system might allow for the use of a slightly smaller turbocharger compared to a constant pressure system for achieving the same performance. This can offer weight and space savings in some applications.
However, the pulse system also has some drawbacks:
- Increased Complexity: The pulse system requires a more complex exhaust manifold design with individual piping groups. This can increase manufacturing cost and maintenance complexity compared to the simpler design of a constant pressure system.
- Limited Applicability: The pulse system is most beneficial for large medium-speed diesel engines with a specific number of cylinders. It might not offer significant advantages for smaller engines or engines with a different cylinder configuration.
Overall, the choice between a pulse system and a constant pressure system depends on the specific application and engine design. For large medium-speed diesel engines where improved low-speed performance and responsiveness are crucial, the pulse system can offer significant advantages. However, its increased complexity needs to be considered.