Proof-of-Concept Numerical Study for NOx Reduction in Diesel Engines Using Enriched Nitrogen and Enriched Oxygen

The medium and heavy duty vehicle industry has fostered an increase in emissions research with the aim of reducing NOx while maintaining power output and thermal efficiency. This research describes a proof-of-concept numerical study conducted on a Caterpillar single-cylinder research engine. The target of the study is to reduce NOx by taking a unique approach to combustion air handling and utilizing enriched nitrogen and oxygen gas streams provided by Air Separation Membranes. A large set of test cases were initially carried out for closed-cycle situations to determine an appropriate set of operating conditions that are conducive for NOx reduction and gas diffusion properties. Several parameters - experimental and numerical, were considered. Experimental aspects, such as engine RPM, fuel injection pressure, start of injection, spray inclusion angle, and valve timings were considered for the parametric study. The numerical factors - initial swirl ratio, adaptive mesh refinement and thickness of enriched nitrogen and oxygen regions were also taken into account. Open-cycle combustion simulations were also carried out for specifically selected operating conditions to assess the potential performance of the dual air combustion concept vs. conventional air-intake. During this proof-ofconcept study, the prospect of using enriched nitrogen and enriched oxygen gas streams for combustion indicated a strong possibility of NOx reduction while maintaining power, thermal efficiency, and managing other emissions output when compared to conventional air-intake systems. Experimental studies and engine testing are in the process of being carried out based on the outcome of current numerical proof-of-concept study.