Abstract
The performance of an automotive turbocharger centrifugal compressor has been studied by developing a comprehensive one-dimensional (1D) code as verified through experimental results and a three-dimensional (3D) model. For 1D analysis, the fluid stream in compressor is modeled using governing gas dynamics equations and the loss mechanisms have been investigated and added to the numerical model. The objective is to develop and offer a 1D model, which considers all loss mechanisms, slip, blockage and also predicts the surge margin and choke conditions. The model captures all features from inlet duct through to volute discharge. Performance characteristics are obtained using preliminary geometry and the blade characteristics. A 3D numerical model was also created and a viscous solver used for investigating the compressor characteristics. The numerical model results show good agreement with experimental data through compressor pressure ratio and efficiency. The effect of the main compressor dimensions on compressor performance has been investigated for wide operating range and the portions of each loss mechanism in the impeller. Higher pressure ratio is achievable by increasing impeller blade height at outlet, impeller blade angle on inlet, diffuser outlet diameter and by decreasing impeller shroud diameter at inlet and blade angle at outlet. These changes may cause unfavorable consequences such as a lower surge margin or shorter operating range, which should be compromised with favorable changes. At lower rotational speeds, impeller skin friction mainly impacts the performance and at higher rotational speeds, impeller diffusion, blade loading and recirculation losses are more important. The results allow the share of each loss mechanism to be quantified for different mass flow rates and rotational speed, shedding new light on which losses are most important for which conditions. For a turbocharger, which must operate over a wide range of conditions, these results bring new insight to engineers seeking to optimize the compressor design as part of an internal combustion engine system.
Highlights
Turbochargers play an important role in the automotive industry and despite moves to electrify road transport, turbocharged internal combustion engines still dominate, likely to be the case for some decades for large commercial vehicles [1]
Diffusion and blade loading loss decreased as mass flow rate increased, explained by the reducing diffusion factor, D, which means the momentum loss of flow due to boundary layer and secondary
Using a 1D model the effect of the impeller and diffuser geometry on the compressor performance when the high pressure ratio at the design point was of interest investigated comprehensively and itemized as below: Impeller blade height at the outlet: Higher value led to higher pressure ratio, lower surge margin, later choke and wider operating range
Summary
Turbochargers play an important role in the automotive industry and despite moves to electrify road transport, turbocharged internal combustion engines still dominate, likely to be the case for some decades for large commercial vehicles [1]. Turbocharger performance, efficiency and stability at different operating conditions are governed mainly by the turbocharger’s compressor and turbine. Since the compressor affects the operation of the whole engine cycle, it is very important to investigate and improve its performance. For an engineer it is very helpful to predict the performance of the machine during the early design stages. Knowledge of the characteristic of compressor, such as efficiency and pressure ratio at different rotational speeds, and adequacy of surge and choke margin at low and high mass flow rates respectively, results in the ability to adjust the machine design to a more favorable operating domain
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