Mwila C. Mulenga

A Thermal Response Analysis on the Transient Performance of Active Diesel Aftertreatment

Diesel fueling and exhaust flow strategies are investigated to control the substrate temperatures of diesel aftertreatment systems. The fueling control includes the common-rail post injection and the external supplemental fuel injection. The post injection pulses are further specified at the early, mid, or late stages of the engine expansion stroke. In comparison, the external fueling rates are moderated under various engine loads to evaluate the thermal impact. Additionally, the active-flow control schemes are implemented to improve the overall energy efficiency of the system. In parallel with the empirical work, the dynamic temperature characteristics of the exhaust system are simulated one-dimensionally with in-house and external codes. The dynamic thermal control, measurement, and modeling of this research intend to improve the performance of diesel particulate filters and diesel NOx absorbers.

Effect of Hydrogen Peroxide on Premixed Iso-Octane/Air Combustion

The effect of hydrogen peroxide (H2 O2 ) on premixed isooctane/air combustion was numerically investigated using detailed chemical kinetics (Peters’ mechanism) via CHEMKIN. Two cases were examined: one-dimensional, planar, adiabatic, premixed flame, which is of fundamental importance to many combustion systems including internal combustion engines, and zero-dimension, adiabatic Homogeneous Charge Compression Ignition (HCCI). Initial conditions investigated were at 298 K and 1 atm for the premixed flame and 343 K and 1 atm for the HCCI. The effects of H2 O2 addition on combustion characteristics including burning velocity, flame temperature, species concentration and ignition delay were deduced. Hydrogen peroxide was utilized as a possible means of emissions reduction. Specifically, the potential of CO reduction due to increased intermediate OH species was studied. The utilization of H2 O2 as a means of controlling ignition timing was also explored.Copyright

Prospect of Reduced CO and NOx Emissions in Diesel Dual Fuel Engines

A numerical analysis of homogeneous natural gas/diesel/air mixture, that could be formed when small amounts of diesel pilot are used in a diesel dual fuel engine or when using natural gas/diesel dual fuel homogeneous charge compression ignition combustion, was studied to provide insight on future experimental investigations to be conducted by the institution. Use was made of Curran’s normal-heptane mechanism in CHEMKIN to deduce its effects on lean fuel/air mixtures with respect to ignition timing and carbon monoxide (CO) and oxides of nitrogen (NOx ) emissions. For the cases considered, increase in the amount of n-heptane addition resulted in advanced ignition closer to TDC thereby increasing peak cylinder pressure and gross IMEP. Increase in the amount of n-heptane addition also resulted in early decomposition of the fuel consequently advancing the production of OH radicals that oxidised the CO. For the same fuel/air mixture strength, increase in the amount of n-heptane addition increased NOx production due to increased peak temperature, residence time and availability of O2 . When using leaner mixtures and small amounts of n-heptane to promote/advance ignition, however, peak cylinder temperatures were reduced and hence comparatively reducing engine-out NOx emissions.Copyright