Abstract
Increasingly stringent regulations to reduce vehicle emissions have made it important to study emission mitigation strategies. Highly accurate control of the air-fuel ratio is an effective way to reduce emissions. However, a less accurate sensor can lead to reduced engine stability and greater variability in engine efficiency and emissions. Additionally, internal combustion engines (ICE) are moving toward higher compression ratios to achieve higher thermal efficiency and alleviate the energy crisis. The objective of this investigation was to analyze the significance of the accuracy of air-fuel ratio measurements at different compression ratios. In this study, a calibrated 1D CFD model was used to analyze the performance and emissions at different compression ratios. The results showed that carbon monoxide (CO) and nitrogen oxides (NOx) were sensitive to the equivalence ratio regardless of the compression ratio. With a slight change in the equivalence ratio, a high compression ratio had little effect on the change in engine performance and emissions. Moreover, with the same air-fuel ratio, an excessively high compression ratio (CR = 12) might result in knocking phenomenon, which increases the fluctuation of the engine output parameters and reduces engine stability. Overall, for precise control of combustion and thermal efficiency improvement, it is recommended that the measurement accuracy of the equivalence ratio is higher than 1% and the recommended value of the compression ratio are roughly 11.
Highlights
The engine efficiency and emissions were systematically evaluated at varied compression ratios (CR = 8,9,10,11,12) at a fixed engine speed = 2000 rpm with different equivalence ratio measurement accuracy around the stoichiometric ratio (14.7)
It is commonly recognized that indicated specific fuel consumption (ISFC), indicated mean effective pressure (IMEP), indicated thermal efficiency (ITE), and exhaust gas temperature (EGT) are the key evaluation indicators of engine efficiency at various fluctuations in air-fuel ratio
A calibrated one-dimensional computational fluid dynamics model was utilized to analyze the effect of equivalence ratio measurement accuracy on engine efficiency and emissions at different compression ratios
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The effectiveness of precise control of the equivalence ratio was mainly influenced by the accuracy of an air-fuel ratio measurement and the precision of the intelligent management system. The studies related to air-fuel ratio control have focused more on advanced intelligent algorithms or control system strategies, while the literature to date is scarce about equivalence ratio measurement accuracy [13]. The precision of the air-fuel ratio was primarily determined by the product of the accuracy of the advanced control strategy and the sensor measurement data. It is of great importance to investigate engine efficiency and emissions for various equivalence ratio measurement accuracies at different compression ratios. The goal of the investigation was to study the effect of air-fuel ratio measurement accuracy on engine efficiency and emissions at varied compression ratios. The fluctuations of engine performance and emissions indicators were quantified based on Gt-power
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