Dissertation/Thesis Abstract

State-based engine models for transient applications with a scalable approach to turbocharging
by Bell, Clay S., Ph.D., Colorado State University, 2015, 156; 3720372
Abstract (Summary)

Microgrids have the potential to improve energy surety, increase the penetration of renewable energy, and provide electrical power in remote areas; however, reduced system inertia contributes to challenges in maintaining power quality during operation. In this dissertation a state-based mean-value turbocharged diesel engine model is developed for applications in microgrid. The model is validated against transient data collected during step load testing at Colorado State University’s Engines and Energy Conversion Laboratory. A controller with an air-fuel ratio based smoke limit and load based gain schedule is implemented to improve agreement with experimental data when compared to a simplified model frequently used in microgrid control studies. The state-based model is capable of variable speed operation, extending the utility to transient applications beyond micro-grid.

Due to the uncertainty around transient performance, lean burn gas engines typically are employed in steady load applications such as distributed generation or industrial systems such as natural gas compression in order to take advantage of the low cost of the fuel, improved efficiency, and reduced emissions. There is significant interest in natural gas engines for microgrids due to the low fuel cost and indications that natural gas supplies would be secure during an interruption of the national electric grid. In addition, replacing diesel engines with gas engines has been identified as a method to reduce cost and emissions associated with drilling and well stimulation. However; both of these applications involve transients which may exceed the capabilities of lean-burn natural gas engines. In this dissertation a state based mean-value turbocharged lean-burn natural gas model is developed to study transient control strategies. Transient data was unavailable; however the model exhibits the expected characteristics during transient loading, namely limited load acceptance capability due to turbocharger lag and narrow air-fuel ratio limits.

Collecting and processing turbocharger performance data to a form appropriate for simulation is one of the more difficult and effort intensive steps when implementing state based engine models. A method is developed to implement non-dimensional performance maps thereby allowing a range of turbochargers to be modeled from the same performance data, reducing the effort required to implement models of different sizes. The non-dimensional maps seek to model the performance of compressor and turbine families in which the geometry of the rotor and housing are similar, and allow the turbocharger to be scaled for simulation in much the same way used to design customized sizes of turbochargers. A method to match the non-dimensional compressor map to engine performance targets by selecting the compressor diameter is presented, as well as a method to match the turbine to the compressor.

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Indexing (document details)
Advisor: Bradley, Thomas, Zimmerle, Daniel
Commitee: Olsen, Daniel, Young, Peter
School: Colorado State University
Department: Mechanical Engineering
School Location: United States -- Colorado
Source: DAI-B 77/01(E), Dissertation Abstracts International
Source Type: DISSERTATION
Subjects: Mechanical engineering
Keywords: Diesel engines, Dynamics, Natural gas engines, Turbochargers
Publication Number: 3720372
ISBN: 978-1-339-01352-7
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