A turbocharger (TC) has to provide a required pressure ratio for efficient combustion and operation of an internal combustion engine (ICE). The turbocharger consists of a turbine and a compressor sides on the same shaft. The turbine utilizes the energy of exhaust gases while the compressor forces the air into the engine. The compressor with a wide operating range is a strict requirement in the automotive industry because the unit has to operate across all of the ICE regimes.
Even though any compressor has a design point, the ability to operate at low and high mass flows is critical for TC compressors. To satisfy the operating range requirement, a designer tries increasing mass flow at choke and decreasing mass flow at surge. This is quite a challenge. For smaller mass flow rates, the impeller outlet and diffuser should be optimized. The choice of a vaneless diffuser is always justified by increased flow range at the cost of efficiency.
To increase the right-most mass flow limit, a designer optimizes the compressor inlet. The common practice is to design blades with large inlet metal angles. Increase in inlet angles open larger area for the flow to pass. This, in turn, leads to large incidence angles at design point. Therefore, many TC compressors are designed with large positive incidence in the design point. The incidence angle increases for every speedline going toward the surge line. Incidence distribution on a TC compressor map is shown in the figure below. It is equal to +12 deg (with respect to tangent) in the design point.
Design point: An operating condition where a compressor reaches maximum efficiency
Compressor Map: Pressure versus mass flow characteristic at different rotational speeds and isoefficiency contours
Speedline: Dependence of pressure on mass flow rate for a given shaft speed
Surge: Left-most point on a compressor map for a given shaft speed
Choke: Right-most point on a compressor map for a given shaft speed
Incidence: The difference between inlet flow and metal angles. If an incidence is small, the flow has less resistance to enter the impeller.
Our next webinar is on Thursday, April 30th! Are you an engineer involved in the Aerospace Industry and its latest development, a manager interested in improving the performance of your aircraft engines, or a student interested in the future of aerospace and the current climate of the industry? You should attend! During the webinar we will be taking a close look at the most recent trends and developments of compressors in aircraft engines with a focus on the key factors for the successful development of aircraft engines.
Key factors for successful development of aircraft engines include technological viability, performance, and re-usability. As one of the industry’s most high-technology products, aircraft engines require innovation in manufacturing and especially in design. They also face the need for continuous development in its technical capabilities in terms of achieving not only higher efficiencies and reliability but also safety and environmental legislations.
It’s Throwback Thursday and we are sharing another of our past webinars! This week’s is called Centrifugal Compressor Design: Can You Really Avoid Choke and Surge?
Surge and choke are inherent, sophisticated phenomena in centrifugal compressor operation. They limit the operational range of any centrifugal compressor and cause severe damage to the machine if it is in surge condition. Several books cover the development of centrifugal compressor surge and choke models that can be applied in compressor control systems in order to avoid surge and choke; while these methods focus retroactively, there are some proactive methods that can be applied during the design phase of the machine. Continue reading “TBT Webinar: Centrifugal Compressor Design: Can You Really Avoid Choke and Surge?”→
Turbochargers, nowadays, are becoming increasingly common in the internal combustion engines of automobiles in order to improve fuel economy and meet government emission regulations. A turbocharger must provide a designed increase in pressure under load condition (design point) while generating enough power at the low end (loss mass flow region). Internal combustion engine working characteristics, however, prevent a centrifugal compressor from generating enough boost at the low end when radial turbine rotational speed is low. Continue reading “Free Webinar: Maximizing Turbocharger Boost with Advanced Design Features”→