Diesel Exhaust Emissions and Mitigations

This chapter presents a concise treatment of diesel engine exhaust emissions and its mitigations. The working principle of the diesel engine is first given to establish the background and further to describe the influence of various parameters that affect the formation of engine exhaust emissions. The factors that influence exhaust emissions are linked to the engine design and the operating factors that promote good fuel-air mixing and combustion. These factors are air induction, fuel injection equipment, fuel injection schemes, in-cylinder gas exchange process and heat transfer. Thermochemistry essentially gives insight to the global reaction kinetics and how this is applied in practical engine combustion determinations in terms of equivalence ratios. Based on these, the fuel spray structure, atomization, penetration and the spray combustion model are described. The formation of exhaust emissions such as carbon monoxide, unburnt hydrocarbon and its intermediates, oxides of nitrogen and soot in diesel engines has been discussed. The techniques of their mitigation from the view of internal factors that deals with the optimization of engine design and it performance, as well as various exhaust after-treatment techniques used for NOx and soot reduction have been briefly discussed

Gas phase thermometry of hot turbulent jets using laser induced phosphorescence

This article is made available through the Brunel Open Access Publishing Fund. Copyright @ 2013 OSAThe temperature distributions of heated turbulent jets of air were determined using two dimensional (planar) laser induced phosphorescence. The jets were heated to specific temperature increments, ranging from 300 – 850 K and several Reynolds numbers were investigated at each temperature. The spectral ratio technique was used in conjunction with thermographic phosphors BAM and YAG:Dy, individually. Single shot and time averaged results are presented as two dimensional stacked images of turbulent jets. YAG:Dy did not produce a high enough signal for single shot measurements. The results allowed for a direct comparison between BAM and YAG:Dy, revealing that BAM is more suitable for relatively lower temperature, fast and turbulent regimes and that YAG:Dy is more suited to relatively higher temperature, steady flow situations

Comparison Of Cavitation Phenomena In Transparent Scaled-Up Single-Hole Diesel Nozzles

The structure and evolution of cavitation in a transparent scaled-up diesel nozzle having a hole inclined at 90, 85, 80 and 0 degree to the nozzle axis has been investigated using high-speed motion pictures, flash photography and stroboscopic visualization. Observations revealed that at the inception stage, cavitation bubbles were not seen at the same locations in all the four nozzles. Cavitation bubbles grew intensively and developed into cloud-like structures. Shedding of the cloud cavitation was observed. When the flow was increased further the cloud-like cavitation bubbles developed into a dense large-scale cavitation cloud extending downstream of the hole. Under this condition the cavitation started mainly as a glassy sheet at the entrance of the hole. Until this stage the spray appeared to be symmetric. When the flow was increased beyond this stage, a sheet of cavitation covered a significant part of the hole on one side, extending to the hole exit. This non-symmetric distribution of cavitation within the hole resulted in a jet, which atomized on the side where more cavitation was distributed and non-atomizing on the side with less cavitation. The distribution of cavitation in the hole was different for different nozzles

Atomisation and Combustion Studies of Diesel Sprays

This thesis addresses two potential problems facing investigators involved in Diesel engine development: fuel atomisation and soot formation. A particular concern has been cavitation in nozzles and its influence on the spray and combustion, investigated through impingement studies, scaled-up transparent nozzle studies and evaluation of hydro grinding effects in a real-size nozzle. Besides cavitation, air dilution effects on soot formation were studied using Laser Induced Incandescence (LII) and two-colour pyrometry. A method was developed to study the instantaneous fuel jet momentum and nozzle discharge coefficient for a non-stationary injection process. The time-resolved fuel jet momentum and nozzle discharge coefficient provides information about the transient phenomena taking place during the injection period due to cavitation. Scaled-up transparent nozzles were used to observe the flow structure within the nozzle hole and to evaluate its effect on the jet emerging from the nozzle flow. The asymmetric distribution of cavitation discovered within the hole had a strong influence on the spray pattern. Under realistic engine conditions, two nozzles each with a hole along the nozzle axis and the same momentum distribution in time, but different inlet geometries, were chosen to study the cavitation effects on combustion. Even though there were differences in the internal turbulence and nozzle discharge coefficient due to cavitation, no major differences were observed in spray angle, penetration, ignition delay, flame structure, temperature or soot concentration between these two equivalent nozzles. LII measurements revealed that soot formation occurred on the inside boundary of the flame periphery where the temperatures are high and oxygen concentration is depleted. In addition, no soot formation was observed initially in the central core of the spray. During later stages, soot production in the interior of the flame caused the soot concentration to be higher in the central region close to the tip of the flame. In diluted environments, the effective ambient oxygen concentration available for reactions is lower, so the reaction rates and flame temperatures are reduced, which delays the first appearance of soot near the nozzle tip and decreases the overall soot formation. However, due to lack of oxygen, the soot that is formed is not effectively oxidised in the later stages, particularly close to the flame tip where very low temperatures were observed

Atomisation and Combustion Studies of Diesel Sprays

This thesis addresses two potential problems facing investigators involved in Diesel engine development: fuel atomisation and soot formation. A particular concern has been cavitation in nozzles and its influence on the spray and combustion, investigated through impingement studies, scaled-up transparent nozzle studies and evaluation of hydro grinding effects in a real-size nozzle. Besides cavitation, air dilution effects on soot formation were studied using Laser Induced Incandescence (LII) and two-colour pyrometry. A method was developed to study the instantaneous fuel jet momentum and nozzle discharge coefficient for a non-stationary injection process. The time-resolved fuel jet momentum and nozzle discharge coefficient provides information about the transient phenomena taking place during the injection period due to cavitation. Scaled-up transparent nozzles were used to observe the flow structure within the nozzle hole and to evaluate its effect on the jet emerging from the nozzle flow. The asymmetric distribution of cavitation discovered within the hole had a strong influence on the spray pattern. Under realistic engine conditions, two nozzles each with a hole along the nozzle axis and the same momentum distribution in time, but different inlet geometries, were chosen to study the cavitation effects on combustion. Even though there were differences in the internal turbulence and nozzle discharge coefficient due to cavitation, no major differences were observed in spray angle, penetration, ignition delay, flame structure, temperature or soot concentration between these two equivalent nozzles. LII measurements revealed that soot formation occurred on the inside boundary of the flame periphery where the temperatures are high and oxygen concentration is depleted. In addition, no soot formation was observed initially in the central core of the spray. During later stages, soot production in the interior of the flame caused the soot concentration to be higher in the central region close to the tip of the flame. In diluted environments, the effective ambient oxygen concentration available for reactions is lower, so the reaction rates and flame temperatures are reduced, which delays the first appearance of soot near the nozzle tip and decreases the overall soot formation. However, due to lack of oxygen, the soot that is formed is not effectively oxidised in the later stages, particularly close to the flame tip where very low temperatures were observed

Cavitation: a Contributary Factor in the Transition from Symmetric to Asymmetric Jets in Cross-flow Nozzles

The structure and evolution of cavitation and its influence on jet patterns from two transparent cross-flow nozzles with holes inclined at 90 degrees (nozzle A) and 80 degrees (nozzle B) to the nozzle axis have been investigated using high-speed motion pictures, flash photography and stroboscopic visualization. At the onset, cavitation inception was in the form of travelling bubbles, which were transported along the flow and clearly detached from the wall. As the flow was increased the bubbles grew and merged into a dense group of bubbles (cloud cavitation), partly unsteady and shedding. Further increasing the flow caused the cavitation at the entrance to transform mainly into a glassy appearance and at this stage the cavitation was well inside the hole and the spray appeared symmetric. When the flow was increased beyond this stage, cavitation extended to the exit of the hole, occupying a significant part of the hole on one side, resulting in a jet that atomized on the side where cavitation was most extensive and a non-atomizing jet on the side with less cavitation. The distribution of cavitation in the hole is very sensitive to the nozzle geometry and it substantially influences the spray dispersion