A Novel Algorithm for Evaluating the Accuracy of In-Cylinder Convective Heat Transfer Coefficient Estimation Models in Port Water-Injected Diesel Engine /
Asad Asghar Janjua
- 118p. Soft Copy 30cm
This research study focuses on evaluating the accuracy of three classical empirical models (Eichelberg, Woschni, and Hohenberg Models) commonly used to estimate the in-cylinder gas-to-wall spatially-averaged-instantaneous-convective heat transfer coefficient (HTC) in a four-stroke high-speed diesel (HSD) engine. The investigation specifically examines effects of port water injection on HTC at low, part, and high load conditions using a retrofitted port water injection system capable of generating variable water injection rates. The absence of a reliable accuracy determination experimental methodology for HTC models in port water injected-diesel engines has prompted the development of an algorithm. This approach utilizes a novel model-based, sequential flow approach using experimental data to develop an algorithm for determination the accuracy of HTC models. The primary data source consists of 36000 experimentally measured in-cylinder pressure values, obtained at 0.36-degree intervals. Separate pressure measurements were conducted for each of the three loading conditions, with six variations in water injection rates within each condition. The algorithm follows a twostep process. First, thermodynamic models are employed to derive essential parameters such as in-cylinder volume, temperature, internal energy, thermodynamic work, and exhaust heat. In the second step, the algorithm calculates the in-cylinder convective heat transfer coefficients using the Eichelberg, Woschni, and Hohenberg models. Notably, these models yield different HTC values for identical engine operating conditions and water injection rates. Using the derived HTC values, the algorithm calculates the heat loss to the cylinder walls, enabling the determination of the engine's cumulative heat release based on thermodynamic relations involving internal energy, work, exhaust heat, and heat loss. By comparing the fuel cumulative heat release with the engine cumulative heat release, the algorithm calculates the engine's combustible efficiency. To identify the heat transfer coefficient model that closely matches a reference value of 98% for engine combustible efficiency, the algorithm compares the calculated values from all testing conditions. The model that generates the highest number of occurrences closest to the referenced 98% is considered the most accurate heat transfer coefficient estimation model xix for high-speed diesel engines utilizing port water injection. The algorithm was implemented on the data obtained from three operating conditions. Each operating condition was tested without water injection and five water injections rates using successive increase in water mass. Total of 36000 in-cylinder pressure values were used for each operating condition and at each water injection rate to obtain all thermodynamic values used in the research. This led to 54 engine combustible values. These engine combustible values then provided 18 most accurate values corresponding to 18 water injection rates for three engine operating conditions. The accuracy of each HTC model was estimated by algorithm at each operating condition and for entire engine operation as well. According to reference value of 98% combustible efficiency; the algorithm calculated that at low and high loading conditions, Hohenberg model estimated most accurate HTC values with 66.66% and 100% accuracy. At medium loading condition, Woschni model estimated most accurate HTC values with 66.66% accuracy. According to algorithm, Hohenberg model estimated HTC values with 67% accuracy for overall engine operation. This research addresses a critical gap in accurately estimating HTC in water-injected diesel engines and provides valuable insights for optimizing engine performance.