This paper describes a comprehensive laboratory project in a third-year&nbsp;applied thermodynamics course. The project provides students with an opportunity to apply concepts from thermodynamics, heat transfer, and numerical methods along with basic data analysis techniques to model the performance of a spark ignition engine. The project allows students to explore ways in which the basic Otto/Diesel/Dual cycle models they encounter in class can be extended to realistically account for non-isentropic and finite-duration heat release effects. In addition, this project provides students with an unique opportunity to bridge the gap between experimentation and model development. In most laboratory-based courses, students assess the validity of analytically or empirically derived results using data they have collected. However, it is rare to find instances in which students use the experimental data they have collected as inputs in models that they are developing.The project is conducted over two weeks. In the first week, students experimentally investigate the performance of a Cooperative Fuel Research (CFR) engine, which is a single-cylinder spark ignition engine with variable compression ratio and spark timing. Students acquire in-cylinder pressure data as a function of crank angle degree for various compression ratios and spark timing. They analyze the data to understand the impact of compression ratio and spark timing on the pressure-volume characteristics and global parameters such as indicated work, engine power and efficiency.In the second week, students develop and validate a numerical model of the compression, heat addition, and expansion strokes of the CFR engine. The numerical model utilizes the Weibe heat release model, which is an empirical model for the combustion process that captures the finite-duration heat release and variable spark timing effects. The Weibe model requires several empirically determined parameters, which the students obtain by fitting their model to the experimental data they collected the previous week. The model is incorporated into a closed-system energy balance along with the ideal gas equation of state to yield a set of differential equations for pressure and temperature. These equations are then numerically integrated to yield the pressure and temperature variation during the combustion process. In addition, the experimental data is also used to determine the polytropic exponents for the compression and expansion processes, which is also incorporated into the model. Students then use their model to investigate sensitivities of engine performance (power, efficiency, fuel consumption) to spark timing, compression ratio and fuel type. The numerical model helps the students more clearly understand the leading order sensitivity of engine performance&nbsp;to the compression ratio and spark timing because stochastic effects such as cycle-to-cycle variations are suppressed in the model.The paper also discusses challenges in the implementation of this project and hurdles encountered by students. Some suggestions to counter these issues are proposed. Finally, the paper concludes with a discussion of additional tasks and refinements that can be incorporated into this project.

Experimental and Computational Investigations of Spark Ignition Engine Performance

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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