Anil Singh Bika

Characterization of Soot Deposition and Particle Nucleation in Exhaust Gas Recirculation Coolers

Cooled exhaust gas recirculation (EGR) is used to control engine out NOx (oxides of nitrogen) emissions from modern diesel engines by re-circulating a portion of the exhaust gases into the intake manifold of an engine after cooling it through a heat exchanger commonly referred to as an EGR cooler. However, EGR cooler fouling due to presence of soot particles and hydrocarbons (HC) in engine exhaust leads to a decrease in cooler efficiency and increased pressure drop across the cooler. This can adversely affect the combustion process, engine durability, and emissions. In this study, a multicylinder diesel engine was used to produce a range of engine out HC and soot concentrations to investigate soot deposition and particle nucleation in an EGR cooler. A portion of the engine exhaust was passed through an EGR cooler, while particle size and HC concentration measurements were made at the cooler inlet and outlet. Tests were conducted over a range of EGR cooler coolant temperatures and engine out soot and HC concentrations to determine the impact on the nucleation and accumulation modes of the exhaust particle size distributions. A reduction in the accumulation mode particle concentration at the EGR cooler outlet was observed for high soot concentrations indicating soot deposition within the EGR cooler. As the EGR coolant temperature was reduced, the outlet accumulation mode particle concentration was reduced further, indicating increased soot deposition in the cooler due to increased thermophoresis. There were no signs of diffusiophoresis due to HC diffusion within the cooler over the range of conditions used in the study. A significant increase in outlet nucleation mode particle concentration was observed for the low soot concentrations. This mode increased with either increasing HC concentration or decreasing coolant temperature, indicating the saturation ratio (SR) dependence of the nucleation mode formation. However, as the soot concentration was increased, the nucleation mode disappeared because of HC adsorption onto the increased soot surface area. Copyright 2012 American Association for Aerosol Research

Comparison of water and butanol based CPCs for examining diesel combustion aerosols

The introduction of condensation particle counters (CPCs) utilizing water as the condensing fluid provides an alternative to traditional butanol based CPCs. Previous evaluations, using atmospheric and laboratory test aerosols, have verified performance. This study compares the performance of multiple water and butanol based CPC models using a diesel engine exhaust challenge aerosol. A total of 5 CPCs used in a scanning mobility particle sizer (SMPS) configuration were compared. TSI models 3786, and 3782 use water as the condensing fluid while models 3010, 3025A, and 3775 use butanol. The test aerosol was generated by a turbocharged, direct injection diesel engine running at constant speed and load, with two fuels, a low sulfur diesel and 99% soy methyl ester biodiesel fuel. Tests were conducted using a single SMPS platform and switching CPCs for each set of tests. In addition, the tests were repeated with long and nano differential mobility analyzer (DMA) columns. Four of the five CPCs agreed well, giving a standard deviation of the overall average geometric mean diameter of less than 1 nm between the 4 CPCs. The fifth CPC, TSI model 3782 did not agree well with the others. The cause of this disagreement is thought stem in part from the use of water as a condensing fluid, but primarily from a lack of sheath air in the 3782 design. The performance of the TSI 3786, an ultrafine water-based CPC with sheath flow showed far better agreement with the butanol CPCs throughout most mobility diameters.

Size and volatility of particle emissions from an ethanol-fueled HCCI engine

ABSTRACT A scanning mobility particle sizer was used to determine the size, number, and mass concentration of particle emissions from an ethanol-fueled homogeneous charge compression ignition (HCCI) engine. Semi-volatile particle composition was characterized using tandem differential mobility analysis (TDMA). Variable temperature thermal conditioning was used to gain insight into particle volatility and a catalytic stripper was used to determine the solid particle distribution. Four engine conditions were evaluated, including low to moderate range loads and motoring (deceleration, coasting). Results indicated that aerosol from a fully premixed HCCI engine under firing conditions is formed almost entirely via nucleation of semi-volatile material originating from the lubricating oil. TDMA analysis indicated 98% of total particle volume evaporated below 100°C. Results pointed towards homogeneous nucleation of precursors derived from the organic species in the lubricating oil, possibly in combination with a sulfur species. The motoring condition, with no fuel injected, exhibited the highest number and mass concentrations. During motoring, there was poor sealing leading to increased atomization of oil and associated ash emissions. Emissions were lower during firing with better sealing and much less atomization, but evaporation of the most volatile fractions of the lubricating oil still led to significant PM emissions consisting of nearly entirely semi-volatile particles containing very little ash.