Mridul Gautam

Characterization of heavy-duty diesel vehicle emissions

Abstract Emissions of heavy duty diesel-powered vehicles were measured at the Phoenix Transit Yard in South Phoenix between 31 March 1992 and 25 April 1992 using the West Virginia University Transportable Heavy-Duty Vehicle Emissions Testing Laboratory (Mobile Lab). Thirteen heavy-duty trucks and buses were tested over this period. The vehicles were operated with diesel No. 2 and Jet A fuels, with and without a fuel additive, and with and without particulate control traps. The chassis dynamometer Mobile Lab tested vehicles over the Central Business District (CBD) driving cycle. Particulate matter in the diluted exhaust was sampled proportionally from a total-exhaust dilution tunnel. Emission rates and compositions of PM 2.5 particulate mass, elements, ions, bulk organic and elemental carbon, and gaseous and particulate polycyclic aromatic hydrocarbons were averaged for various classes of fuels and particulate matter control. Emission rates for PM 2.5 mass averaged 0.2 and 1 g mile −1 for trucks and buses with and without particulate traps, respectively. Emission rates for elemental carbon averaged 0.02 and 0.5 g mile −1 for trucks and buses with and without particulate traps, respectively. Diesel particulate exhaust was comprised mainly of organic and elemental carbon (80–90%) and sulfate (up to 14%). The new diesel source composition profiles are similar to one determined earlier in Phoenix. Polycyclic aromatic hydrocarbons comprised no more than a few percent of the particulate organic carbon but their relative abundances may be useful for distinguishing diesel emissions from those of other combustion sources.

Computer simulation of bubbles in large-particle fluidized beds

A distinct element model is used to study the hydrodynamics of large-particle fluidized beds. The computed bubble rise velocity, voidage variations, averaged particle/particulate and fluid velocities are compared with the other continuum theory based on two fluid model. Based on the averaged particle/particulate velocities in a grid cell, deformation of the particle layers predicted by the two fluid model and the distinct element method are also compared. The predicted characteristics of bubble formation, motion, and eruption at the bed surface are in good qualitative agreement with the experimental observations. The quantitative differences in predicting the above parameters along with the advantages and limitations of two approaches for the case of a single isolated bubble rising in a two-dimensional fluidized bed are discussed.

Effect of diesel soot contaminated oil on engine wear — investigation of novel oil formulations

Abstract Exhaust Gas Re-circulation (EGR) has been found to be very effective in reducing emissions of oxides of nitrogen, for light duty diesel engines. However, EGR results in a sharp increase in particulate matter emissions in heavy-duty diesel engines. The effects of soot contaminated engine oil on wear of engine components was examined using a statistically designed experiment. The three oil properties studied were phosphorous level, dispersant level and sulfonate substrate level. The above three variables were formulated at two levels: High (1) and Low (−1). This resulted in a 23 matrix (eight oil blends). The effect of soot was also taken into consideration, which resulted in a 24 factorial experiment. A three-body wear machine was designed and developed to simulate and estimate the extent of wear. Ball-on-flat-disk tests were conducted to qualitatively study wear by comparing wear scars due to soot with wear scars due to a known abrasive (alumina). A Scanning Electron Microscope (SEM) was used to study the microstructures of the wear scars. Surface chemical analysis was performed on soot particles and wear scars using Energy–Dispersive X-ray Analysis (EDAX). Results show that diesel soot interacts with oil additives reducing the oils anti-wear properties possibly by abrasive wear mechanism. Statistical analysis (GLM) showed that the phosphorous level plays a dominant role on oils wear performance. The effect of dispersant level was not very significant, though on an average, higher dispersant levels reduced wear. The effect of sulfonate was not revealed within the range of these concentrations. Ball-on-flat-disk type tests also revealed the increased wear due to the presence of soot. SEM studies of Wear Scar Diameters suggest that soot is abrasive.

Diesel and CNG Transit Bus Emissions Characterization By Two Chassis Dynamometer Laboratories: Results and Issues

Emissions of six 32 passenger transit buses were characterized using one of the West Virginia University (WVU) Transportable Heavy Duty Emissions Testing Laboratories, and the fixed base chassis dynamometer at the Colorado Institute for Fuels and High Altitude Engine Research (CIFHAER). Three of the buses were powered with 1997 ISB 5.9 liter Cummins diesel engines, and three were powered with the 1997 5.9 liter Cummins natural gas (NG) counterpart. The NG engines were LEV certified. Objectives were to contrast the emissions performance of the diesel and NG units, and to compare results from the two laboratories. Both laboratories found that oxides of nitrogen and particulate matter (PM) emissions were substantially lower for the natural gas buses than for the diesel buses. It was observed that by varying the rapidity of pedal movement during accelerations in the Central Business District cycle (CBD), CO and PM emissions from the diesel buses could be varied by a factor of three or more. The driving styles may be characterized as aggressive and non-aggressive, but both styles followed the CBD speed command acceptably. PM emissions were far higher for the aggressive driving style. For the NG fueled vehicles driving style had a similar, although smaller, effect on NO{sub x}. It is evident that driver habits may cause substantial deviation in emissions for the CBD cycle. When the CO emissions are used as a surrogate for driver aggression, a regression analysis shows that NO{sub x} and PM emissions from the two laboratories agree closely for equivalent driving style. Implications of driver habit for emissions inventories and regulations are briefly considered.

Parametric studies on the formation of diesel particulate matter via nucleation and coagulation modes

Abstract The objective of this study is to develop a physical model that accurately accounts for the nucleation, coagulation, and condensation processes in the formation of particulate matter (PM) inside the exhaust plume of the diesel-fueled vehicles. The PM concentration has been predicted based on the fuel sulfur content, fuel-to-air ratio, exhaust flow rate, and the ambient conditions. It was predicted that the critical nucleus diameter of the particles decreased by approximately 30% and the number concentration increased by a factor of 6 with the increase in relative humidity from 10% to 90% for a fuel with 50 ppm sulfur content. The parametric studies suggested that the condensation effects are very important near the stack. Ignoring the contribution from condensation term decreased PM count median diameter from 52 to 10 nm . A fair agreement is observed between the numerically predicted PM size distribution and concentration and the experimentally measured values.

Idle emissions from heavy-duty diesel vehicles: review and recent data.

Abstract Heavy-duty diesel vehicle idling consumes fuel and reduces atmospheric quality, but its restriction cannot simply be proscribed, because cab heat or air-conditioning provides essential driver comfort. A comprehensive tailpipe emissions database to describe idling impacts is not yet available. This paper presents a substantial data set that incorporates results from the West Virginia University transient engine test cell, the E-55/59 Study and the Gasoline/Diesel PM Split Study. It covered 75 heavy-duty diesel engines and trucks, which were divided into two groups: vehicles with mechanical fuel injection (MFI) and vehicles with electronic fuel injection (EFI). Idle emissions of CO, hydrocarbon (HC), oxides of nitrogen (NOx), particulate matter (PM), and carbon dioxide (CO2) have been reported. Idle CO2 emissions allowed the projection of fuel consumption during idling. Test-to-test variations were observed for repeat idle tests on the same vehicle because of measurement variation, accessory loads, and ambient conditions. Vehicles fitted with EFI, on average, emitted [~20 g/hr of CO, 6 g/hr of HC, 86 g/hr of NOx, 1 g/hr of PM, and 4636 g/hr of CO2 during idle. MFI equipped vehicles emitted ~35 g/hr of CO, 23 g/hr of HC, 48 g/hr of NOx, 4 g/hr of PM, and 4484 g/hr of CO2, on average, during idle. Vehicles with EFI emitted less idleCO, HC, and PM, which could be attributed to the efficient combustion and superior fuel atomization in EFI systems. Idle NOx, however, increased with EFI, which corresponds with the advancing of timing to improve idle combustion. Fuel injection management did not have any effect on CO2 and, hence, fuel consumption. Use of air conditioning without increasing engine speed increased idle CO2, NOx, PM, HC, and fuel consumption by 25% on average. When the engine speed was elevated from 600 to 1100 revolutions per minute, CO2 and NOx emissions and fuel consumption increased by >150%, whereas PM and HC emissions increased by ~100% and 70%, respectively. Six Detroit Diesel Corp. (DDC) Series 60 engines in engine test cell were found to emit less CO, NOx, and PM emissions and consumed fuel at only 75%of the level found in the chassis dynamometer data. This is because fan and compressor loads were absent in the engine test cell.

Criteria pollutant and greenhouse gas emissions from CNG transit buses equipped with three-way catalysts compared to lean-burn engines and oxidation catalyst technologies

Engine and exhaust control technologies applied to compressed natural gas (CNG) transit buses have advanced from lean-burn, to lean-burn with oxidation catalyst (OxC), to stoichiometric combustion with three-way catalyst (TWC). With this technology advancement, regulated gaseous and particulate matter emissions have been significantly reduced. Two CNG transit buses equipped with stoichiometric combustion engines and TWCs were tested on a chassis dynamometer, and their emissions were measured. Emissions from the stoichiometric engines with TWCs were then compared to the emissions from lean-burn CNG transit buses tested in previous studies. Stoichiometric combustion with TWC was effective in reducing emissions of oxides of nitrogen (NOX), particulate matter (PM), and nonmethane hydrocarbon (NMHC) by 87% to 98% depending on pollutants and test cycles, compared to lean combustion. The high removal efficiencies exceeded the emission reduction required from the certification standards, especially for NOX and PM. While the certification standards require 95% and 90% reductions for NOX and PM, respectively, from the engine model years 1998–2003 to the engine model year 2007, the measured NOX and PM emissions show 96% and 95% reductions, respectively, from the lean-burn engines to the stoichiometric engines with TWC over the transient Urban Dynamometer Driving Schedule (UDDS) cycle. One drawback of stoichiometric combustion with TWC is that this technology produces higher carbon monoxide (CO) emissions than lean combustion. In regard to controlling CO emissions, lean combustion with OxC is more effective than stoichiometric combustion. Stoichiometric combustion with TWC produced higher greenhouse gas (GHG) emissions including carbon dioxide (CO2) and methane (CH4) than lean combustion during the UDDS cycle, but lower GHG emissions during the steady-state cruise cycle. Implications: Stoichiometric combustion with three-way catalyst is currently the best emission control technology available for compressed natural gas (CNG) transit buses to meet the stringent U.S. Environmental Protection Agency (EPA) 2010 heavy-duty engine NOX emissions standard. For existing lean-burn CNG transit buses in the fleet, oxidation catalyst would be the most effective retrofit technology for the control of NMHC and CO emissions.

Influence of Real-World Engine Load Conditions on Nanoparticle Emissions from a DPF and SCR Equipped Heavy-Duty Diesel Engine

The experiments aimed at investigating the effect of real-world engine load conditions on nanoparticle emissions from a Diesel Particulate Filter and Selective Catalytic Reduction after-treatment system (DPF-SCR) equipped heavy-duty diesel engine. The results showed the emission of nucleation mode particles in the size range of 6-15 nm at conditions with high exhaust temperatures. A direct result of higher exhaust temperatures (over 380 °C) contributing to higher concentration of nucleation mode nanoparticles is presented in this study. The action of an SCR catalyst with urea injection was found to increase the particle number count by over an order of magnitude in comparison to DPF out particle concentrations. Engine operations resulting in exhaust temperatures below 380 °C did not contribute to significant nucleation mode nanoparticle concentrations. The study further suggests the fact that SCR-equipped engines operating within the Not-To-Exceed (NTE) zone over a critical exhaust temperature and under favorable ambient dilution conditions could contribute to high nanoparticle concentrations to the environment. Also, some of the high temperature modes resulted in DPF out accumulation mode (between 50 and 200 nm) particle concentrations an order of magnitude greater than typical background PM concentrations. This leads to the conclusion that sustained NTE operation could trigger high temperature passive regeneration which in turn would result in lower filtration efficiencies of the DPF that further contributes to the increased solid fraction of the PM number count.

Differential pressure measurements in a slugging fluidized bed

Abstract Detailed information on local fluid bed behavior cannot be obtained using global instrumentation. However, dual static pressure probes (DSPP) which measure local axial differential pressures can be used to infer the presence of bubbles or slugs in a fluid bed. DSPP consist of two probe stems, one positioned vertically above the other, connected to a differential pressure transducer. Response of DSPP has been modeled and is fast enough to capture transient phenomena in a fluid bed, provided that a low-dead-volume transducer is used. DSPP with 1.27-cm, 1.9-cm, and 2.54-cm stem spacings have been used to measure slugging properties of a 13.97-cm diameter air-fluidized bed filled with 3.175-mm nylon spheres. Over 500 20-second pressure traces were digitally recorded for two distributor types, a variety of bed heights, air flow rates and probe positions. Slugging frequency was found from selected traces using the autocorrelation function, Fourier transform and power spectral density function, and was shown to decrease with bed height. Slug velocity was found using cross-correlation of signals from two DSPP, and was shown to increase with air throughput and decrease slightly with bed height.

Lateral sloshing in partially filled elliptical tanker trucks using a trammel pendulum

Fluid sloshing in partially filled tanker trucks is the problem herein being addressed. In these vehicles, lateral fluid sloshing during turning and sudden lane change manoeuvres is the main cause for low rollover threshold. Fluid models and equivalent mechanical spring-bob and pendulums models have been used to simulate the lateral fluid sloshing in various tank shapes. A novel idea of an elliptical trammel pendulum for elliptical tank geometries is proposed. The bases of selecting the parameters of this pendulum such as pendulum mass, length of arms, and location of fixed mass are derived and verified using a finite element approach.