A Micro-Variable Circular Orifice (MVOC) Fuel Injector with Variable Spray Angles and Patterns for Reducting NOx Emissions from Diesel Engines

Diesel engines are widely used due to their high fuel efficiency. However, conventional diesel engines have high NOx and soot emissions. Selective catalytic reduction (SCR) for NOx reduction is less accepted by the construction industry due to complexity and cost. In-cylinder NOx reduction is more desirable. When low temperature combustion and/or premixed charge compression ignition (PCCI) combustion reduces engine-out NOx and soot simultaneously, the conventional multi-hole injector limits operation ranges for PCCI. One major reason is due to the fixed injection spray angle. Currently, PCCI can only operate in low to medium loads. Conventional fixed-spray-angle nozzles have to be compromised for low-load PCCI and high-load conventional combustion. A larger spray angle for high loads will bring severe wall wetting and oil dilution for early and late injections. A fixed narrow spray angle optimized for low-load PCCI usually generates more soot for high-load combustion. The fixed spray angle is hardly adaptive to the moving combustion chamber geometry. Thus, a variable spray angle injector is desired. This research is to conduct combustion simulation and spray diagnostics to evaluate the feasibility of a key enabling technology¿a mixed-mode fuel injector with a micro-variable circular orifice (MVCO). The innovative MVCO injector provides a variable spray angle, which is smaller for early injection and larger for injection near top dead center (TDC), and a variable spray pattern, which is a conical mist-like spray for early injection with less penetration and turns into a multi-jet for later injection with higher penetration. The MVCO provides an optimized spray pattern to minimize surface-wetting, oil dilution, and emissions. For the first time, the MVCO enables a continuously variable spray pattern for combustion optimization with broad loads, speeds, and injection timings. The new MVCO fuel injector has the potential to offer a cost-effective solution for engine retrofit to reduce NOx through the following means: 1. Significantly reduces idle speed, thus reducing the fuel consumption and NOx. 2. Provides a flexible spray angle and pattern to match combustion chamber geometry and simultaneously reduce soot, NOx, HC, and CO. 3. Enables low-temperature premixed combustion with homogeneous atomization. Preliminary experiment results show that the MVCO fuel injector is capable of reducing NOx emissions by about 40 percent, and reduces fuel consumption between 8 and 10 percent at low to medium loads. The potential application of the MVCO fuel injector includes off-road diesel equipment and on-highway diesel engines. The MVCO injector is potentially an effective low-cost solution for new engines and engine retrofits for NOx reductions.