On Soot Sampling: Considerations when Sampling for TEM Imaging and Differential Mobility Spectrometer

Particulate matter (PM) has been sampled from a compression ignition engine using a differential mobility spectrometer (Cambustion DMS 500) and for imaging in a transmission electron microscope (TEM) with the aim of coupling these two measuring techniques. A known issue when coupling these two methods is that a devise like the DMS samples all PM, and the TEM only soot. To help resolve this issue, a thermal denuder was designed and built to remove all volatile organic compounds (VOC) from the sample prior to entering the DMS. For TEM imaging, soot was either collected directly onto a TEM grid using the thermophoretic effect or collected onto quartz filters with the soot then transferred onto the TEM grids. The direct to grid technique did not work after the denuder due to the gas temperature being too low for the thermophoretic effect; hence the reason to collect some soot using the quartz filters. Soot was removed from the filters using an ethanol wash/sonication technique. Morphology; diameter of gyration, projected area, primary particle size and fractal dimension have been compared between the two TEM sampling techniques, with or without the denuder. Denuder effectiveness has been assessed using TGA analysis of sampled soot. Issues concerning the sampling process itself are outlined. A comparison between the TEM and the DMS results is conducted with the discrepancies between them discussed. Direct and filter sampling gave similar results as long as the sonication process and grid prep is done properly, otherwise the filter wash technique results in a number of clusters of agglomerates which distorts the post processing and morphological data

Numerical investigation of particles turbulent dispersion in channel flow

This paper investigates the performance of Reynolds-averaged Navier-Stokes model on dispersion of particles in wall turbulence. A direct numerical simulation of wall-bounded channel flow with particles suspensions was set as a benchmark. The standard k-ω model coupled with two different eddy interaction models was used in Reynolds-averaged Navier-Stokes model and compared to the direct numerical simulation. Detailed comparisons between direct numerical simulation and Reynolds-averaged Navier-Stokes model on particle distribution evolving over time were carried out

Experimental studies of autoignition and soot formation of diesel surrogate fuels

Computational simulation has undergone vast development for internal-combustion engine research as a time- and costsaving tool. Yet combustion simulation for conventional hydrocarbon petroleum fuels faces difficult challenges since such fuels have very complex compositions, consisting of many different molecular species, for which data are sparse. The use of surrogate fuels for combustion simulation could provide a solution to this problem. In this investigation, n-heptane and mixtures of n-heptane and toluene were studied within a broad range of potential surrogate diesel fuels, and the ignition delay and soot formation trends were compared with those of diesel fuel. Ignition delays show good agreement with those for diesel fuel and it was also possible to replicate partially the soot formation behaviour for certain engine conditions. Further investigation is needed to find a surrogate fuel that closely matches over the range of operating conditions of a diesel engine.Engineering and Physical Sciences Research Council EP/G0277730/

Effects of biodiesel injector configuration and its injection timing on performance, combustion and emissions characteristics of liquid ammonia dual direct injection engine

Ammonia is a promising carbon-neutral fuel that can be stored and transported in liquid form, offering a viable alternative to diesel fuel. In addition, it can be used directly in diesel engine in its liquid form in dual fuel mode. Hence, a single-cylinder diesel engine was modified to implement two common rail (CR) injection systems, allowing the direct injection of liquid ammonia with biodiesel. As biodiesel was used for a pilot fuel with lower injected mass, this study aims to investigate the influence of the number of nozzles in the biodiesel injector on the performance, combustion, and emissions characteristics of the liquid ammonia-biodiesel dual direct injection engine. Therefore, the number of holes in the CR injector was closed in various configurations to improve injection parameters. Furthermore, various biodiesel start of injection (SOI) timings were tested, ranging from −24 to −14 CAD, while the SOI of ammonia was kept at −10 CAD with an ammonia mass ratio of 67.2%. The results showed that welding three nozzles from the original six-nozzle injector resulted in a remarkable 29.2% reduction in NH3 and CO emissions. Furthermore, the highest indicated thermal efficiency of 39.7% was obtained for the injector with 3b nozzles. Additionally, late injection of both fuels led to an increase in particulate matter emissions, from 10.5 to 15.2 mg/m3, due to the formation of fuel-rich zones at high temperatures. However, it reduced NOx and CO emissions by 1.4 and 4.4 g/kWh, respectively, compared to the early SOI of biodiesel. Moreover, the lowest N2O emission was measured at 115.0 ppm in the earliest SOI of biodiesel at −24 CAD

Experimental and numerical study on direct injection of liquid ammonia and its injection timing in an ammonia-biodiesel dual injection engine

Ammonia is an alternative carbon-free fuel that can be easily stored in a liquid phase, unlike hydrogen, and then directly utilized in diesel engines. Hence, a single-cylinder diesel engine was retrofitted for direct injection of liquid ammonia with pilot ignition of biodiesel in dual fuel combustion mode. The effects of the liquid phase of ammonia and ammonia energy share (AES) on combustion, emissions, and engine performance were investigated and compared with pure biodiesel operation. Moreover, various ammonia injection timings were studied to improve ammonia/biodiesel combustion and reduce emissions. A CFD model was developed and validated with experimental data to study ammonia/biodiesel sprays, combustion characteristics, and emissions formation. The results showed higher AES significantly reduced the local cylinder temperature due to the strong cooling effects of ammonia, therefore, a maximum AES of 50% was achieved. Increasing AES to 50% decreased combustion duration and combustion phasing by 26.2 and 4.4 CAD, respectively. However, it deteriorated the indicated thermal efficiency (ITE) by 1.3 percent point compared to pure biodiesel. Furthermore, retarding ammonia injection from −25 to −10 CAD significantly reduced NOx, CO, and ammonia emissions by 31.4%, 39.6%, and 31.3%, respectively. Ultimately, the optimal operating condition was suggested when ammonia was injected at −10 CAD and biodiesel at −16 CAD with AES of 50%

Effect of Excess Air Ratio and Temperature on NOx Emission from Grate Combustion of Biomass in the Staged Air Combustion Scenario

The combustion of biomass, in this case demolition wood, has been investigated in a grate combustion multifuel reactor. In this work a temperature range of 850-1000 degrees C is applied both for staged air combustion and nonstaged combustion of biomass to investigate the effects of these parameters on the emission levels of NOx, N(2)O, CO, hydrocarbons (C(x)H(y)),) and different other components. The composition of the flue gas is measured by four advanced continuous gas analyzers including gas chromatograph (GC), two Fourier transform infrared (FTIR) analyzers, and a conventional multispecies gas analyzer with fast response time. The experiments show the effects of staged air combustion, compared to nonstaged combustion, on the emission levels clearly. A NOx reduction of up to 85% is reached with staged air combustion. An optimum primary excess air ratio of 0.8-0.95 is found as a minimizing parameter for the NOx emissions for staged air combustion. Air staging has, however, a negative effect on N(2)O emissions. Even though the trends show a very small reduction in the NOx level as temperature increases in nonstaged combustion, the effect of temperature is not significant for NOx and C(x)H(y), neither in staged air combustion or nonstaged combustion, while it has a great influence on the N(2)O and CO emissions, with decreasing levels with increasing temperature

NOx emission reduction by staged combustion in grate combustion of biomass fuels and fuel mixtures

NOx and N2O emissions have been investigated for different pelletized biomass fuels and fuel mixtures thereof both with and without air staging in a grate fired multi-fuel reactor. The fuels investigated are wood, demolition wood and coffee waste, and selected mixtures of these. The multi-fuel reactor was operated at close to constant operating conditions due to impactor (ELPI) measurements, with a total excess air ratio of about 1.6, and a primary excess air ratio of about 0.8 in the air staging experiments. The reactor set point temperature was held constant at 850 degrees C. NOx emission levels as a function of air supply mode and fuel nitrogen content are reported, showing a large NOx reduction potential, up to 91% and corresponding to less than 20 ppm NOx at 11% O-2 for a fuel containing about 3 wt.% fuel-N, using air staging. The effect on N2O, however, is adverse at the selected set point temperature and optimum primary excess air ratio for NOx reduction. The effect of fuel mixing and fuel nitrogen content on the conversion of fuel nitrogen to NOx is also reported and discussed. Fuel mixing has a positive influence on the NOx emission level, but a negative influence on the overall conversion factor for fuel-N to NOx and N2O