Turbochargers are becoming an essential device in internal combustion engines as they boost the intake air with more pressure in order to increase the power output. These devices are normally designed for a single steady design point but the pulsating flow delivered from the internal combustion engine is everything but steady. The efficiency drop experienced in the off-design points by the fixed geometry turbochargers have made some research groups to look into new variable geometry solutions for turbocharging. A nozzle ring is a device which normally achieves a higher performance under design conditions, but the efficiency rapidly drops at off-design conditions. In this paper, a variable angle nozzle ring is designed and implemented in the model of a radial turbine of a turbocharger in order to study its potential when working under real internal combustion engine cycles. To understand the profit margin the turbine performance is compared with two turbines with the same impeller geometry: one without nozzle ring and one with a nozzle ring with a fixed angle. The results show that the maximum efficiency angle function calculated for the variable angle nozzle ring achieves an improvement in the total efficiency of 5 % when comparing with a turbine with a fixed angle and 18 % when comparing with a vaneless turbine. The improved guidance achieved due to the variable blade angle leads to less turbine losses and therefore more mechanical energy can be extracted from the exhaust mass flow throughout all the combustion cycle but a further study should be made in order to match all the engine operations points. Notably, taking the pulsating boundary conditions into consideration, a remarkable improvement is achieved already for the fixed angle nozzle ring.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:kth-174345 |
| Date | January 2015 |
| Creators | Carrasco Mora, Enrique |
| Publisher | KTH, Kraft- och värmeteknologi |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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