Engine Exhaust Stream Research Articles

Modeling of diesel particulate filter temperature dynamics during exotherm using neural networks

Diesel Particulate Filter (DPF) in the diesel engine exhaust stream needs frequent regeneration (exotherm) to remove captured particulate matter (PM, or soot) without damaging to the porous DPF structure by controlling the peak temperatures and temperature gradients across the DPF. In this study, temperature distribution in a DPF is measured at 42 strategic locations in the test DPF under various regeneration conditions of exhaust flow rates, regeneration temperatures and soot loads. Then a data-based model with feed-forward neural network architecture is designed to model the thermal gradients and temperature dynamics of the DPF during the regeneration process. The neural network feature vector selection, network architecture, hyperparameter calibration process, measured data preprocessing, and experimental data acquisition procedure are evaluated. Over 7,400 experimental data points at various regeneration temperatures, flow rates and soot loads are used in training and validating the neural network model. It is found that the neural network model can accurately predict the 42 DPF bed temperatures simultaneously at different locations, and the time series analysis of both model-predicted and experimentally measured temperatures shows a good correlation. This indicates that the currently developed neural network model can provide spatial distribution of temperature in the DPF, and comprehend the nonlinearity of the temperature dynamics due to DPF soot load at exothermic conditions. These results demonstrate that the data-based model has capability in predicting thermal gradients within a DPF, aiding in determining a safer DPF regeneration strategy, onboard diagnostics and DPF development.

An Examination of Heat Transfer Dynamics in Pulsating Air Flow within Pipes: Implications for Automotive Exhaust Engines

The detailed understanding of heat transfer in the pulsating airflow in the pipe is critical to reducing heat losses in the engine exhaust stream and improving catalyst performance. In the present investigation, we have scrutinized the impact of pulsation frequencies ranging from 0-90 Hz on the flow velocity field and the consequent heat transfer through a horizontal pipe wall. The Nusselt numbers were evaluated at three distinct cross-sectional points moving from upstream to downstream, by systematically modulating the frequency. Temporal variations in the velocity field and temperature were captured utilizing particle image velocimetry (PIV) and dual-thermocouple probes, respectively. Intriguingly, while the Nusselt number for steady flow at 0 Hz closely adhered to Gnielinski’s equation, the pulsating flow demonstrated a peak between 25-35 Hz, a pattern not predicted by the prevailing quasi-steady-state theory. The observed frequency response of turbulence was found to be congruous with the Nusselt number, indicating that the heightened heat transfer at frequencies of 25-35 Hz could be attributed to the enhanced turbulence and the temperature gradient between the fluid and the wall surface during the deceleration phase in the hysteresis of turbulence in the pulsating flow. The unique frequency characteristics of heat transfer that were uncovered in this study, with respect to both flow velocity and temperature, offer valuable insights for devising strategies to mitigate heat loss during ignition and idling. Furthermore, these findings provide robust benchmarks for validating numerical simulations of pulsating flows in real-life automotive engines.

Effects of Biodiesel Addition on the Physical Properties and Reactivity of the Exhaust Soot Particles from Diesel Engine

The present study investigated the effects of adding 20 vol.% biodiesel to petroleum diesel (to produce a mixture termed B20) on the physical properties and reactivity of the resulting exhaust soot particles. Tests were performed at different engine loads of a constant speed, and the soot particles from the combustion of B20 and petroleum diesel fuel (DF) were collected from the engine exhaust stream. Transmission electron microscopy and Raman spectroscopy were employed for the analysis of soot morphology and nanostructure. The thermogravimetric analysis was used to determine the oxidative reactivity of the soot. For both the DF and B20 soot, increased engine loads result in soot aggregates with more compact morphology and primary soot particles with larger size and more organized structure. Compared to the DF soot, the B20 aggregates have a slightly more compact morphology and smaller primary particle size. No appreciable differences are observed in nanostructure between the DF and B20 soot. The thermogravimetric analysis demonstrates that the B20 soot is associated with lower peak temperature, burnout temperature and apparent activation energy, suggesting that it is more reactive than the DF soot.

3D printed catalytic converters with enhanced activity for low-temperature methane oxidation in dual-fuel engines

Catalytic converters with non-linear channel structures were prepared using 3D printing and tested in the oxidation of methane in a simulated dual-fuel engine exhaust stream. The design used a simple repeating angular offset between adjacent layers, which was sufficient to introduce complexity with minimal software programming. All 3D printed substrates were mechanically stable and, following washcoating with a composite catalyst, demonstrated higher catalytic activity in methane oxidation than a commercial honeycomb substrate. The methane conversion at e.g. 510 °C was 12.6% on the commercial sample, 72.6% for 90°, 80.1% for both 30° and 45°, and 89.6% for the 60° oriented structures. This enhancement is attributed to the increased turbulence/mass transfer and surface area than are possible using conventional straight-channelled substrates. Computational fluid dynamics (CFD) analysis confirmed that the higher methane conversion over 3D printed substrates is due (at least partially) to its higher turbulence kinetic energy. Backpressures over the 3D printed structures were also experimentally measured and compared with the conventional honeycomb monolith.

Carbon Dioxide Capture From Internal Combustion Engine Exhaust Using Temperature Swing Adsorption

Abstract: In order to reduce the CO2 emissions in the transportation sector, one can electrify the vehicle, switch to biofuel, or capture and store CO2 on board. In this study, integration of an on board CO2 capture and storage unit with an internal combustion engine has been proposed. The technology can be applied for various internal combustion or Stirling engines with targeted applications in the transportation sector. Truck transport for goods delivery is used as an example for on board CO2 capture and storage system design. The investigated system integrates a temperature swing adsorption system for CO2 capture with a turbo-compressor system to compress and liquefy the captured CO2 using the waste heat of the exhaust gases of the engine. Energy and exergy analyses of the proposed CO2 captured system are studied in details. The CO2 capture system for engine exhaust stream (car, truck, bus, ship or train) can capture 90% of the emitted CO2, without any energy penalty. This system can be integrated into overall mobility system (fuel-engine-CO2-fuel), where captured CO2 can be recycled as conventional liquid or gaseous fuels produced from renewable energy sources. Keywords: Carbon Dioxide Capture; Internal Combustion Engine; Exergy Analysis; Temperature Swing Adsorption; System Design and Integration; Heat Exchanger Network.

Modeling of Three-Way Catalyst Dynamics for a Compressed Natural Gas Engine during Lean–Rich Transitions

The main objective of the present research activity was to investigate the effect of very fast composition transitions of the engine exhaust typical in real-world driving operating conditions, as fuel cutoff phases or engine misfire, on the aftertreatment devices, which are generally very sensitive to these changes. This phenomenon is particularly evident when dealing with engines powered by natural gas, which requires the use of a three-way catalyst (TWC). Indeed, some deviations from the stoichiometric lambda value can interfere with the catalytic converter efficiency. In this work, a numerical “quasi-steady” model was developed to simulate the chemical and transport phenomena of a specific TWC for a compressed natural gas (CNG) heavy-duty engine. A dedicated experimental campaign was performed in order to evaluate the catalyst response to a defined λ variation pattern of the engine exhaust stream, thus providing the data necessary for the numerical model validation. Tests were carried out to reproduce oxygen storage phenomena that make catalyst behavior different from the classic steady-state operating conditions. A surface reaction kinetic mechanism concerning CH4, CO, H2, oxidation and NO reduction has been appropriately calibrated at different λ values with a step-by-step procedure, both in steady-state conditions of the engine work plan and during transient conditions, through cyclical and consecutive transitions of variable frequency between rich and lean phases. The activity also includes a proper calibration of the reactions involving cerium inside the catalyst in order to reproduce oxygen storage and release dynamics. Sensitivity analysis and continuous control of the reaction rate allowed evaluating the impact of each of them on the exhaust composition in several operating conditions. The proposed model predicts tailpipe conversion/formation of the main chemical species, starting from experimental engine-out data, and provides a useful tool to evaluate the catalyst’s performance.

Role of dispersant on soot-induced wear in Cummins ISB engine test

Wear performance of two fully formulated engine oils was evaluated using the Cummins ISB engine test. One of the oil formulations used a multifunctional DVII (Dispersant Viscosity Index Improver) component with enhanced antiwear characteristics to improve durability of engine components while the other formulation comprised of a conventional additive package. After the completion of engine-dynamometer tests, valvetrain components operating primarily in boundary lubrication regime were inspected for wear and weight loss in order to understand soot induced wear effects. In addition, soot was extracted and characterized using temperature resolved XRD, TEM, XANES, BET, Raman and EDS. XRD phase analysis of residue left behind after soot oxidation showed presence of crystalline compounds embedded in the soot structure (CaSO4, Ca3(PO4)2, Zn3(PO4)2 and ZnO). These species form ash pre-cursors which get trapped in the DPF (Diesel Particulate Filter) placed in the engine exhaust stream. The turbostratic structure of both soot samples remains the same prior to oxidation; however, the embedded crystalline and amorphous species in the soot structure slightly change with oil formulation. Surface area of the soot measured using BET was found to be inversely proportional to the weight of residue. Additionally, used oil analysis was performed to understand variation in viscosity, wear elements and soot content before and after the test. Findings in this study provide deeper insights into the mechanism for improved wear protection provided by DVII.

On-board thermochemical energy recovery technology for low carbon clean gasoline direct injection engine powered vehicles

Exhaust gas fuel reforming is a catalytic process that reclaims exhaust energy from the high temperature engine exhaust stream to drive catalytic endothermic fuel reforming reactions; these convert hydrocarbon fuel to higher enthalpy hydrogen-rich gas known as reformate. This technique has the potential to improve the thermal efficiency of internal combustion engines, as well as to simultaneously reduce gaseous and particulate emissions. This study demonstrates a novel, prototype exhaust gas fuel reformer integrated with a modern, turbocharged, 4-cylinder gasoline direct injection engine and analyses the effects on engine performance, combustion characteristics and emissions. The results suggest that exhaust gas fuel reforming raises the engine fuel efficiency through a combination of: exhaust energy recovery; improved engine thermal efficiency; and enhanced combustion at highly dilute operation, which considerably reduces NOx emissions by up to 91% and improves engine fuel consumption by up to 8%. The presence of hydrogen and exhaust gas diluents in the combustion charge also reduces particle formation for lower total particulate matter emissions (up to 78% and 84% for number and mass, respectively).

Nanostructure and oxidative properties of soot from a compression ignition engine: The effect of a homogeneous combustion catalyst

This study examined the influence of an iron-based homogeneous combustion catalyst on the oxidative behaviour and nanostructural characteristics of soot emitted from a single-cylinder compression ignition engine. The catalyst was homogeneously added into a commercial diesel as the reference at ultra low dosage ratios. Smoke opacity was measured using a smoke opacimeter in the engine exhaust stream to indicate the overall soot emission intensity. Soot particles were also sampled while the engine was maintained in steady-state operations and fuelled with the reference diesel and the catalyst treated fuels, respectively. The soot samples were subjected to thermogravimetric analysis (TGA) to study their oxidation reactivities in air, and transmission electron microscopy (TEM) for morphological characterisations. The smoke opacity results showed 7.3–39.5% less soot emissions when the catalyst was applied, depending on the catalyst dosage ratio. The TGA results revealed that soot from the catalyst treated fuels possessed higher oxidative reactivity as indicated by ignition at lower temperatures and faster oxidation rates than those of soot from the reference diesel. This tendency was more remarked as the catalyst dosage ratio increased. Subsequent TEM imaging analyses observed that the irregularly shaped, aggregated soot particles were made of a number of spherical primary particles. Smaller and more narrowly-distributed primary soot particles with the catalyst treated fuels than those of the reference diesel were evident. High-resolution TEM imaging revealed graphitic crystallite structures of the soot samples from both catalyst-treated and -untreated fuels with no obvious variations in the nuclei core areas, suggesting that the internal structure of the soot was not affected by the catalyst. It was evident that iron ions from the catalyst were more involved in the soot oxidation process, rather than in the early soot formation stage, and eventually resulted in smaller and narrowly-distributed primary soot particles.

Correlation Between Speciated Hydrocarbon Emissions and Flame Ionization Detector Response for Gasoline/Alcohol Blends

The U.S. renewable fuel standard has made it a requirement to increase the production of ethanol and advanced biofuels to 36 billion by 2022. Ethanol will be capped at 15 billion, which leaves 21 billion to come from other sources such as butanol. Butanol has a higher energy density and lower affinity for water than ethanol. Moreover, alcohol fueled engines in general have been shown to positively affect engine-out emissions of oxides of nitrogen and carbon monoxide compared with their gasoline fueled counterparts. In light of these developments, the variety and blend levels of oxygenated constituents is likely to increase in the foreseeable future. The effect on engine-out emissions for total hydrocarbons is less clear due to the relative insensitivity of the flame ionization detector (FID) toward alcohols and aldehydes. It is well documented that hydrocarbon (HC) measurement using a conventional FID in the presence of oxygenates in the engine exhaust stream can lead to a misinterpretation of HC emissions trends for alcohol fuel blends. Characterization of the exhaust stream for all expected hydrocarbon constituents is required to accurately determine the actual concentration of unburned fuel components in the exhaust. In addition to a conventional exhaust emissions bench, this characterization requires supplementary instrumentation capable of hydrocarbon speciation and response factor independent quantification. Although required for certification testing, this sort of instrumentation is not yet widely available in engine development facilities. Therefore, an attempt is made to empirically determine FID correction factors for oxygenate fuels. Exhaust emissions of an engine fueled with several blends of gasoline and ethanol, n-butanol and iso-Butanol were characterized using both a conventional FID and a Fourier transform infrared. Based on these results, a response factor predicting the actual hydrocarbon emissions based solely on FID results as a function of alcohol type and content is presented. Finally, the correlation derived from data presented in this study is compared with equations and results found in the literature.

Active Regeneration of Diesel Particulate Filter Employing Microwave Heating

Wall-flow diesel particulate filters (DPFs) are considered the most effective devices for the control of diesel particulate emissions. A requirement for the reliable operation of the DPFs, however, is the periodic and/or continuous regeneration of the filters. While microwave heating has been considered a potential active regeneration method for the DPFs, past studies on the technology have identified several technical problems leading to filter failure. The problems are mainly associated with the use of inappropriate filter materials for the microwave system and the generation of local hotspots due to uneven microwave heating, resulting in the physical damage to the filters. The objective of this study was to develop and demonstrate the technology employing a microwave-absorbing filter material coupled with an effective waveguide design for the reliable regeneration of DPFs. In this study, a well-equipped diesel emission control laboratory was established to conduct the experiments. The experimental facilities included a 6-kWe diesel generator, an exhaust flow control system, a diesel particulate filter system, a microwave energy supply system, a soot sampling system, a differential-pressure measurement system, and a temperature measurement system. The DPF was a silicone carbide wall-flow monolith filter enclosed in a quartz filter holder. A commercial 1.4-kWe microwave oven was modified to accommodate the quartz holder and a waveguide was engineered to evenly supply the microwave energy to the enclosed filter to achieve filter regeneration. In the experiments, the diesel engine exhaust was lined up to flow through the filter with a fixed flow rate. The microwave regeneration was triggered after a specific amount of soot loading was reached based on the differential pressure drop reading. The results have indicated that the designed system has been able to achieve uniform temperature profiles both in the radial and the vertical DPF positions. The off-line regeneration of DPF by microwave energy has been observed to be highly efficient in terms of energy consumption and regeneration efficiency. The DPM filtration efficiency has remained comparably high after 150 cycles of filtration/regeneration with no apparent physical damage to the DPF being observed. The on-line microwave regeneration of the DPF, however, is not as efficient as the off-line regeneration due to the insufficient oxygen concentration in the engine exhaust stream.

06/00127 A fuzzy gain scheduling PI controller application for an interconnected electrical power system: Çam, E. and Kocaarslan, I. Electric Power Systems Research, 2005, 73,(3), 267–274

Results are presented for in situ measurement of CO2, NOx and CO concentrations in exhaust emitted from an automotive diesel engine. These data were obtained with a series of temperature-controlled sensor probes and compared to exhaust concentrations measured simultaneously with an exhaust motor analyzer. The CO2 sensor is a Nernstian type with a Li2CO3|Au sensing electrode, a Li3PO4 electrolyte and a Li2TiO3 + TiO2|Au reference electrode. The total NOx sensor measures the difference between potential responses of two porous Pt electrodes on an ion-conducting stabilized cubic zirconia support. The potential difference results because one Pt electrode is covered with a catalyst to achieve a locally equilibrated NOx mixture, whereas the other electrode exposed to the sensing gas mixture, pre-equilibrated at a different temperature. The CO sensor is a resistive type and responds to selective sorption of reducing species. All sensor types have simple planar configurations but require accurate temperature control to deal with significant fluctuations in the engine exhaust stream. A constant sensor temperature of typically 400 °C is achieved with a ceramic heater strip and tight control using a direct digital PID algorithm. The NOx sensor requires a second temperature-controlled pre-conditioning filter. This filter is integrated in the probe and controlled with a thermo-coax heating wire and another PID implementation. Generally, the sensors responses in the engine agree with the laboratory tests, but calibration errors resulted due to lack of thermal homogeneity of the sensor. In addition, some drift is observed due to particulate contamination from the exhaust stream. The CO2 sensor appeared to be the most robust, though the probe signal may have been influenced by the evacuation effect at high gas velocities present in the car exhaust.

Temperature-controlled CO, CO 2 and NO x sensing in a diesel engine exhaust stream

Results are presented for in situ measurement of CO 2, NO x and CO concentrations in exhaust emitted from an automotive diesel engine. These data were obtained with a series of temperature-controlled sensor probes and compared to exhaust concentrations measured simultaneously with an exhaust motor analyzer. The CO 2 sensor is a Nernstian type with a Li 2CO 3|Au sensing electrode, a Li 3PO 4 electrolyte and a Li 2TiO 3 + TiO 2|Au reference electrode. The total NO x sensor measures the difference between potential responses of two porous Pt electrodes on an ion-conducting stabilized cubic zirconia support. The potential difference results because one Pt electrode is covered with a catalyst to achieve a locally equilibrated NO x mixture, whereas the other electrode exposed to the sensing gas mixture, pre-equilibrated at a different temperature. The CO sensor is a resistive type and responds to selective sorption of reducing species. All sensor types have simple planar configurations but require accurate temperature control to deal with significant fluctuations in the engine exhaust stream. A constant sensor temperature of typically 400 °C is achieved with a ceramic heater strip and tight control using a direct digital PID algorithm. The NO x sensor requires a second temperature-controlled pre-conditioning filter. This filter is integrated in the probe and controlled with a thermo-coax heating wire and another PID implementation. Generally, the sensors responses in the engine agree with the laboratory tests, but calibration errors resulted due to lack of thermal homogeneity of the sensor. In addition, some drift is observed due to particulate contamination from the exhaust stream. The CO 2 sensor appeared to be the most robust, though the probe signal may have been influenced by the evacuation effect at high gas velocities present in the car exhaust.

The Selective Non-Catalytic Removal (SNCR) of Nitric Oxides From Engine Exhaust Streams: Comparison of Three Processes

Three processes for the selective non-catalytic removal (SNCR) of nitric oxides from engine exhaust gases are compared. The three processes are similar but each uses a different chemical agent: ammonia, urea, or cyanuric acid. A number of operating conditions have been studied. In particular, results for the removal of nitric oxide are significantly different for the three processes as the oxygen concentration varies. Ammonia, urea, and cyanuric acid were found to be most effective at low, intermediate, and high oxygen concentrations, respectively. The implications of these results for a range of engines and engine applications are discussed.

Electron microscope comparisons of fine and ultra-fine carbonaceous and non-carbonaceous, airborne particulates

Particulate matter (PM) from a number of specific sources has been collected on carbon/formvar-coated 100-mesh nickel or copper grids for transmission electron microscopy (TEM) using a thermal precipitator. These sources included diesel truck exhaust, graphitic PM from brake-shop environments, jet engine exhaust streams, and a wide range of general airborne PM for comparison. Individual PM TEM images were compared with corresponding selected-area electron diffraction patterns and energy-dispersive (X-ray) spectra. Diesel PM was characterized by aggregate branching of carbonaceous spherules while graphitic PM consisted of layered carbon, crystalline carbon nanotubes and fullerene-related nanocrystals, and prominent mixtures of inorganic microcrystals. Essentially, all airborne PM collected was characterized by variations of cluster or aggregate morphologies and non-carbonaceous PM was mostly micro- or nanocrystalline. Mixtures of carbonaceous and nanocrystalline PM were also observed. Although tedious, individual PM analysis and comparison appears to be a necessary strategy to elucidate the apparent toxic effects increasingly identified with ultra-fine and nanoparticulates in the air.

Role of Methyl Nitrate in Plasma Exhaust Treatment

There is growing interest in the use of a nonthermal plasma combined with a catalyst for NOx removal from diesel engine exhaust streams. Such exhaust streams contain excess oxygen (typically 6−10%), low concentrations of hydrocarbons (typically 100−1000 ppm), and significant concentrations of water (typically 5−12%). Conversion of NOx to environmentally acceptable compounds, without requiring a scrubber or an added reductant, is the desired end result. In our research we observe the formation of substantial amounts of methyl nitrate (CH3ONO2) by the plasma discharge. Since similar compounds have been proposed as reaction intermediates in NOx removal, tests were performed to elucidate the effect of CH3ONO2 in the plasma−catalyst system. CH3ONO2 was prepared and added to the gas blend on test equipment simulating a diesel exhaust gas. A dielectric barrier plasma discharge was followed by a zeolite-based catalyst. Methyl nitrate introduced upstream of the plasma discharge is largely unreacted upon passing through the plasma. CH3ONO2 arriving at the catalyst is converted to methanol and NO2. While methyl nitrate was shown to be formed in this system, it is not a significant intermediate in the mechanism of conversion of NOx to nitrogen.

A signal processing framework based on dynamic neural networks with application to problems in adaptation, filtering, and classification

We present a coherent neural net based framework for solving various signal processing problems. It relies on the assertion that time-lagged recurrent networks possess the necessary representational capabilities to act as universal approximators of nonlinear dynamical systems. This applies to system identification, time-series prediction, nonlinear filtering, adaptive filtering, and temporal pattern classification. We address the development of models of nonlinear dynamical systems, in the form of time-lagged recurrent neural nets, which can be used without further training. We employ a weight update procedure based on the extended Kalman filter (EKF). Against the tendency for a net to forget earlier learning as it processes new examples, we develop a technique called multistream training. We demonstrate our framework by applying it to 4 problems. First, we show that a single time-lagged recurrent net can be trained to produce excellent one-time-step predictions for two different time series and also to be robust to severe errors in the input sequence. Second, we model stably a complex system containing significant process noise. The remaining two problems are drawn from real-world automotive applications. One involves input-output modeling of the dynamic behavior of a catalyst-sensor system which is exposed to an operating engine's exhaust stream, the other the real-time and continuous detection of engine misfire.

Chemical Sensors Play Growing Role in Analytical Sciences

Chemical sensors turn up in familiar places. As one common example, many modern automobiles contain a sensor that measures the concentration of oxygen in the engine exhaust stream. The signal from the sensor helps a microprocessorcontrolled device constantly adjust the engine's fuel/air ratio to provide the best tradeoffs, under changing conditions, between maximum mileage and minimum pollution. Chemical sensors are also playing an increasingly large role in the analytical sciences. Like the device in the auto, they provide real-time, on-site information about the presence and concentration of chemicals in a given environment. As a result, they often can eliminate the need for sample collection, sample preparation, and later analysis in a lab. These advantages, in turn, often can aid the development of cleaner and more efficient industrial processes, more dependable health care procedures, and more effective environmental cleanup efforts. The 1989 International Chemical Congress of Pacific Basin Societies...