Test System Design And Combustion Character Study Of A Small Diesel Engine With Oxygen Enriched Inlet

The application of oxygen-enriched combustion technology in the diesel engines can not only raise the thermal efficiency of combustion and make its power performance and fuel economy improved, but also reduce soot emission significantly. This has great significance for the realization of energy saving and emission reduction in the vehicle. Active study is conducted on oxygen-enriched inlet combustion in diesel engines by many researchers and made a series of substantive progress. The method of the combination of simulations and experiments to explore the influence of oxygen-enriched inlet on combustion and emission performance in diesel engines was adopted in this paper. It provides reference for further study on the application of oxygen enriched combustion technology in diesel engines.Based on a single-cylinder direct injection, air-cooled diesel engine, a small diesel engine oxygen enriched combustion test system was devised. The test station includes engine test-bed, intake and exhaust system and data acquisition and processing system. When the construction and commissioning of the whole system is completed, the stability test of system is carried out for an hour at the rated speed varying load condition. Test results show that the system not only has the advantages of simple operation, stable running, safe and reliable, but also can achieve real-time display, automatic storage and effective processing of all the test data.In order to study the change of the performance and emissions of the diesel engine with the wide range of inlet oxygen concentration, the test system was applied to the oxygen enriched combustion test. The inlet oxygen concentration is 21%、24%、27% and 30% by volume. Test condition: rated speed 3000 r·min-1, no-load, medium load and high load. The results show that, at the range of 21%~30% of volume percentage of oxygen, with the increase of inlet oxygen concentration, the specific fuel consumption of the diesel engine reduced initially and then increased within a small range, the exhaust temperature increased and the soot emission significantly decreased, but the NO_x emission greatly increased.The engine operating condition was simulated by application FIRE software coupling the n-heptane reduced mechanism containing polycyclic aromatic hydrocarbon(PAH) formation. The simulation and its verification test were both carried out under the maximum torque point. Then, the oxygen enriched combustion was simulated on the model and the simulated condition was oxygen volume fraction from 21% to 30%. The simulation results show that, the oxygen enrichment(from 21% to 30%)increase the peak cylinder pressure of 3.32%, advance the start of combustion of 1.6 deg and rise the peak of average temperature in cylinder and wall heat flux. Among them, at the condition of 24% O2, the change of the results is the most significant. Benzene(A1) is one of the precursor of soot generated, the analysis of its impress-cuts of the mass distribution field in cylinder shows that, the increase of oxygen concentration can significantly inhibit the formation of benzene. But the oxygen enrichment makes the combustion more sufficient, cased a rise in the cylinder temperature, an extension in high temperature area, and an increment in the NO_x emission.