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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Method for removing soot from exhaust gases

A method for oxidizing soot from diesel exhaust gas from a diesel engine. The method involves providing a diesel particulate filter for receiving the diesel exhaust gas; coating a catalyst composition on the diesel particulate filter; and contacting the soot from the diesel exhaust gas with the catalyst coated diesel particulate filter at a temperature sufficient to oxidize the soot to carbon dioxide. The catalyst composition is a doped or undoped manganese oxide octahedral molecular sieve (OMS-2) material. A diesel exhaust gas treatment system that includes a diesel particulate filter for receiving diesel exhaust gas from a diesel engine and collecting soot; and a catalyst composition coated on the diesel particulate filter. The catalyst composition is a doped or undoped manganese oxide octahedral molecular sieve (OMS-2).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Effect of nitric oxide and exhaust gases on gasoline surrogate autoignition: iso-octane experiments and modeling

Exhaust gas recirculation (EGR) is widely used in advanced internal combustion engines to reduce engine emissions as well as control combustion phasing. Among various species present in EGR gases, CO 2 and H 2 O are two major components that can thermally and chemically affect fuel autoignition. It is of fundamental interest to isolate the thermal and chemical effects of CO 2 and H 2 O on fuel autoignition, especially as such an effort has not been reported in the literature. Moreover, nitric oxide (NO) is known to exhibit strong chemical effects on fuel autoignition, which in turn affects engine combustion phasing. The effects of ultra-low NO addition (< 100 ppm) on fuel autoignition at low temperatures are also not well understood. Recognizing these problems, autoignition experiments of iso-octane (a major gasoline surrogate component) in air are performed in this study using a rapid compression machine at varying compressed pressures, equivalence ratios, dilution levels with an EGR gas analogue (consisting of CO 2 , H 2 O, O 2 , and N 2 ) and N 2 only, and varying amounts of NO addition. Furthermore, the thermal and chemical effects of the EGR gas analogue are isolated and evaluated by comparing the ignition delay time datasets of EGR and N2-only diluted cases.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Catalytic Removal of Oxygen and Pollutants in Exhaust Gases from Pressurized Oxy-Combustors

The primary goal of this project was to develop and validate advanced catalytic materials and systems for purifying the flue gas generated from pressurized oxy-combustors in an effort to achieve the purity specifications of carbon dioxide (CO 2 ) streams required by the U.S. Department of Energy (USDOE) for application in enhanced oil recovery. The technology has shown great potential for improving energy efficiency, simplifying process complexity, and lowering costs compared with current state-of-the-art oxy-combustion flue gas purification technologies. Laboratory studies were conducted for the development, characterization, and screening of metal catalysts for residual oxygen (O 2 ) reduction with methane (CH 4 ) and multifunctional carbon catalysts for combined nitrogen oxides (NO x ), sulfur oxides (SO x ), and mercury (Hg) removal. A bench-scale reverse-flow fixed-bed (RFFB) reactor and a trickle-bed direct-contact cooler (DCC) reactor capable of treating 15 standard liters per min of pressurized oxy-combustion flue gas were fabricated and tested with both a simulated flue gas in the laboratory and a slipstream of actual flue gas at a 100 kW th Staged, Pressurized Oxy-Combustion (SPOC) pilot facility. Process simulation and techno-economic studies were performed to evaluate the energy efficiency and cost of the developed catalytic flue gas purification process integrated into a conceptual 550-MWe SPOC power plant. The goal and objectives of the project have been successfully accomplished. A cobalt-manganese (CoMn) oxide catalyst was developed and demonstrated in the bench-scale RFFB reactor in either a reverse-flow or one-direction flow mode of operation that met the success criterion of performance for residual O 2 reduction. A carbon catalyst was developed and demonstrated in the bench-scale DCC reactor that met the success criterion of performance for combined NO x /SO x /Hg removal. Slipstream testing of the integrated DCC-RFFB system at the SPOC pilot facility demonstrated stable operation and verified the superior performance obtained in the laboratory. The techno-economic analysis showed that a 550-MWe SPOC plant integrated with the catalytic flue gas purification process would result in costs of electricity of $\$$96.94/MWh and $\$$80.27/MWh in two assessed cases compared with $\$$91.07/MWh reported for the USDOE’s Current Technology Case, which generated only a partially pure CO 2 stream. On the basis of the results and findings from this project, scale-up studies of materials production and system demonstration and optimization studies of reactors and processes are recommended at the next stage of technology development.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2023

Low soot stoichiometric compression-ignition combustion

A combustion system including a combustion mechanism that injects oxygenated fuel into a combustion chamber. The oxygenated fuel mixes with the intake air in the combustion chamber where the air-fuel ratio in a portion of the combustion chamber is stoichiometric. The combustion mechanism includes an ignition mechanism that ignites the air-fuel mixture that generates a threshold number of particulates during combustion of the air-fuel mixture. The combustion system further includes an exhaust gas recirculation (EGR) device that recirculates a portion of the exhaust gases back into the combustion chamber. The EGR device recirculates the portion of the exhaust to lower combustion temperature resulting in reduced amount of nitrogen oxide in the exhaust. The combustion system further includes a three-way catalytic converter in line with the exhaust channel to convert a second portion of the exhaust gases, leading to lower pollutant emissions than conventional combustion systems.

Pickett, Lyle M.↗
DOE OSTI2019

GDCI transient EGR error compensation

A GDCI engine recirculates exhaust gases to a combustion chamber using desired early injection parameters for a steady state engine operation from a controller. An engine control system detects a load increase relative to the steady state engine operation, and insufficient recirculated exhaust gases to the combustion chamber are delivered in response to the detected load increase as a result of transport delays. A last fuel injection into the combustion chamber during an engine cycle with multiple fuel injections is delayed as compared to the steady state engine operation. Combustion phasing within the combustion chamber is retarded in response to the delayed injection.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2020

Mercury Speciation During Vitrification of LAW

n this work, laboratory and engineering-scale tests were conducted that mimic the reactive environment of the Hanford Tank Waste Treatment and Immobilization Plant (WTP) low activity waste (LAW) melter and off-gas system in order to assess the speciation of mercury at select points in the processing system. The experimental protocols, test equipment, feed materials used, and rationale for testing are detailed in the Test Plan for this work. Particular attention was paid to the amount and speciation of mercury in submerged bed scrubber (SBS) solutions, which are intended to be recycled back to the melter feed at the WTP. Results are presented from detailed mercury analysis of these solutions using Environmental Protection Agency (EPA) Method 1630 and modifications to this method for dimethyl mercury and methyl mercury as well as EPA Method 1631 and modifications to this method for total, dissolved, elemental, suspended, and ionic mercury. Testing was conducted in two separate sets of experiments: (1) One set of tests (crucible-scale furnace tests) that involved heating small batches of mercury-spiked melter feed in crucibles to determine the amount of mercury retained in the glass and the species of mercury in the exhaust gases; (2) A second set of tests (DM10 melter tests) was planned that involved creating LAW melter plenum gas compositions using the DM10 melter system, injecting mercury into the off-gas stream, and passing that stream though a reactor that simulates various plenum gas conditions. Operational issues led to the need to use one of the VSL DM100 melters in place of the planned DM10 melter for these tests. The speciation of mercury after exposure to those conditions was monitored. In both sets of tests, the exhaust gases were run through a scrubber that was intended to mimic the LAW SBS in order to determine how much of the mercury exiting the melter would be retained in the primary off-gas system fluids and in what form. After passing through the SBS, the exhaust stream was analyzed to determine particulate, ionic, elemental, and total mercury passing downstream of the SBS. In tests employing gases derived from the DM100 melter that were spiked with elemental mercury, the processing system provided gas temperatures and residence times that are representative of the WTP LAW vitrification system in order to assess the effect of those conditions on mercury speciation. The Decontamination Factor (DF) across the system in the tests with mercury-spiked DM100 melter exhaust was determined using the analytical data from EPA Method 30B (Fluegas Adsorption Mercury Speciation (FAMS TM )) exhaust samples and the amount of mercury detected in the SBS solutions. Mercury species used in melter feed crucible scale tests were divalent (chloride and iodide), monovalent (chloride and fluoride), and elemental mercury. Individual tests included only a single form of mercury in the feed. The results for total mercury mass balances in the crucible tests are also presented.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2019

First results from the implementation of the ITER diagnostic residual gas analyzer prototype at Wendelstein 7-X

Fusion reactors and long pulse fusion experiments heavily depend on a continuous fuel cycle, which requires detailed monitoring of exhaust gases. We have used a diagnostic residual gas analyzer (DRGA) built as a prototype for ITER and integrated it on the most advanced stellarator fusion experiment, Wendelstein 7-X (W7-X). The DRGA was equipped with a sampling tube and assessed for gas time of flight sample response, effects of magnetic field on gas detection and practical aspects of use in a state of the art fusion environment. The setup was successfully commissioned and operated and was used to observe the gas composition of W7-X exhaust gases. The measured time of flight gas response was found to be in the order of a second for a 7 m sample tube. High values of magnetic field were found to affect the partial pressure readings of the DRGA and suggest that additional shielding is necessary in future experimental campaigns.

47 OTHER INSTRUMENTATION↗
DOE OSTI2023

CO 2 coverage on Pd catalysts accelerates oxygen removal in oxy-combustion systems

Oxy-combustion systems result in enriched CO 2 in exhaust gases; however, the utilization of the concentrated CO 2 stream from oxy-combustion is limited by remnant O 2 . CH 4 oxidation using Pd catalysts has been found to have high O 2 -removal efficiency. Here, in this study, the effect of excess CO 2 in the feed stream on O 2 removal with CH 4 oxidation is investigated by combining experimental and theoretical approaches. Experimental results reveal complete CH 4 oxidation without any side-products, and a monotonic increase in the rate of CO 2 generation with an increase in CO 2 concentration in the feed stream. Density-functional theory calculations show that high surface coverage of CO 2 on Pd leads to a reduction in the activation energy for the initial dissociation of CH 4 into CH 3 and H, and also the subsequent oxidation reactions. A CO 2 -rich environment in oxy-combustion systems is therefore beneficial for the reduction of oxygen in exhaust gases.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Performance of a Natural Gas Solid Oxide Fuel Cell System With and Without Carbon Capture

The fuel cell program at the United States Department of Energy (DOE) National Energy Technology Laboratory (NETL) is focused on the development of low-cost, highly efficient, and reliable fossil-fuel-based solid oxide fuel cell (SOFC) power systems that can generate environmentally-friendly electric power with at least 90 percent carbon capture. NETL’s SOFC technology development roadmap is aligned with near-term market opportunities in the distributed generation sector to validate and advance the technology while paving the way for utility-scale natural gas (NG)- and coal-derived synthesis gas-fueled applications via progressively larger system demonstrations. The present study represents a part of a series of system evaluations being carried out at NETL to aid in prioritizing technological advances along research pathways to the realization of utility-scale SOFC systems, a transformational goal of the fuel cell program. In particular, the system performance of utility-scale NG fuel cell (NGFC) systems with and without carbon dioxide (CO2) capture is presented. The NGFC system analyzed features an external auto-thermal reformer (ATR) feeding the fuel to the SOFC system consisting of planar anode-supported SOFC with separated anode and cathode off-gas streams. In systems with CO2 capture, an air separation unit (ASU) is used to provide the oxygen for the ATR and for the combustion of unutilized fuel in the SOFC anode exhaust along with a CO2 purification unit to provide a nearly pure CO2 stream suitable for transport for usage in enhanced oil recovery operations or for storage in underground saline formations. Remaining thermal energy in the exhaust gases is recovered in a bottoming steam Rankine cycle while supplying any process heat requirements. A reduced order model (ROM) developed at the Pacific Northwest National Laboratory (PNNL) is used to predict the SOFC performance. The ROM, while being computationally effective for system studies, provides other detailed information about the state of the stack, such as the internal temperature gradient, generally not available from simple performance models often used to represent the SOFC. Such additional information can be important in system optimization studies to preclude operation under off-design conditions that can adversely impact overall system reliability. The NGFC system performance was analyzed by varying salient system parameters, including the percent of internal (to the SOFC module) NG reformation—ranging from 0 to 100 percent—fuel utilization, and current density. The impact of advances in underlying SOFC technology on electrical performance was also explored.

solid oxide fuel cell (SOFC), natural gas fuel cel↗
DOE OSTI2020

Aging of Concrete for the Evaluation of Repair Materials to Protect the Walls of the HCAEX Tunnel at Savannah River - 20301

H-Canyon, located in the Savannah River site, is a unique facility for chemical reprocessing of plutonium, highly-enriched uranium, and other radioactive materials. The exhaust gases of the H-Canyon are sent through the H-Canyon Exhaust (HCAEX) tunnel for contamination removal. Robotic inspections of the tunnel revealed significant degradation of the reinforced concrete structure that was associated with acid attack, and could compromise the structural stability of the tunnel. Thus, the identification and evaluation of potential repair materials that could be applied on the degraded walls to mitigate and prevent further degradation is of significant interest to the Department of Energy and the Savannah River representatives. This research effort has been divided into two phases: 1) Development and evaluation of aged concrete under accelerated aging conditions (which is the focus of this paper) and 2) Evaluation of potential repair materials applied on aged and non-aged concrete under simulated aggressive conditions. In order to develop and evaluate concrete samples exposed to accelerated aging conditions in simulated aggressive environments, a literature review of the HCAEX tunnel was conducted that included 1) characterization and extent of the concrete damage, 2) environmental conditions inside the tunnel and 3) primary deterioration mechanisms. In addition, potential coatings and/or repair materials for degraded concrete surfaces exposed to aggressive environments (primarily acidic) were selected from the literature review and the most common testing and measurements for evaluating acid attack phenomena, erosion, etc. were reviewed. From the literature review findings, a preliminary bench-scale test plan for the concrete aging was developed, including accelerated aging tests with aggressive conditions (acid fumes, humidity, etc.). Concrete samples were exposed to the aging accelerated conditions (e.g. immersion in acid solutions) and visual inspection, mass loss and pH change (acid solution) were recorded over time. Correlations between the visual inspection, mass loss and pH changes results and the aging time or the aging conditions were developed. Specimens submitted to the highest acid concentration showed the fastest and most intense degradation. The type of coarse aggregate (limestone) used for the concrete seemed to be the cause of the fastest aging observed, compared to the cement paste. The research findings created the foundation for the ongoing investigation, in which new concrete samples with a mix design similar to the HCAEX tunnel will be tested and will serve as the substrate for testing the selected coatings and /or repair materials. In this paper, the literature review and preliminary results from the aging tests are provided. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2019

Vehicle Exhaust Monitoring Applications using loT platform

Vehicle emission is a major source of air pollution. A significant number of deaths is associated with air pollution. The existing vehicle emission monitoring system is unable to mitigate the pollution properly. Real-time pollution measurement is necessary to address the problem more precisely. The purpose of this project is to develop novel Vehicle Emission Monitoring Applications (VEMA) using the real-time measurement of pollutants from a vehicle tailpipe where exhaust gases enter the environment. As a part of the project, 2 technologies have been used for exhaust gas monitoring. First, an off-the-shelf exhaust gas monitoring prototype has been acquired. Second, a brand new platform was developed using off-the-shelf components. The project focused on predictive application for smart mobility and for large large fleet companies and enterprises. A data collection methodology was developed and tested by collecting close to 20 hours of data within Washington State under varying speeds, altitudes, road conditions etc. An approach for data curation was also used and finally, a simple Machine Learning was used for recognizing patterns between inputs such as vehicle speed and altitude and output such as NOx emission from vehicle exhaust pipe.

47 OTHER INSTRUMENTATION↗
DOE OSTI2023

The Impact of Oxidation-Induced Degradation On Materials Used in Hydrogen-Fired Microturbines

Hydrogen-fueled microturbines are being considered as part of the future green microgrid. However, the use of hydrogen as a fuel presents new challenges for selection and development of suitable high temperature materials for hydrogen combustion. The burning of hydrogen is expected to result in higher operating temperatures and higher than typically observed water vapor contents in exhaust gases versus burning natural gas. In the present work, foil specimens of various Fe- and Ni-based alloys were oxidized in air + 10 % H 2 O and air + 60% H 2 O for up to 5,000 h at 700 °C to simulate the exhaust atmosphere of natural gas and hydrogen-fueled microturbines. Here, the impact of alloy composition and water vapor content on the oxidation/ volatilization induced loss of wall thickness was experimentally evaluated. Enhanced external oxidation and volatilization of Cr 2 O 3 and Ti-doped Cr 2 O 3 scales was observed in air + 60% H 2 O compared to air + 10% H 2 O. No significant impact of the higher water vapor content was observed on Al 2 O 3 scales formed on Fe-based alumina forming alloys. Lifetime modeling was employed to predict the combined effects of water vapor content, gas flow rates, temperature and alloy composition on the oxidation-induced lifetime of the investigated materials.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Dicarboxylic acid emissions from a GDI engine equipped with a catalytic gasoline particulate filter

Dicarboxylic acids play an important role in atmospheric chemistry, yet their emissions from primary sources, such as internal combustion engines, has not been extensively studied. In this paper, KOH impregnated quartz filters were loaded with exhaust gases from a gasoline direct injection (GDI) engine equipped with a catalytic gasoline particulate filter (GPF). All filters were analyzed for carboxylic and dicarboxylic acids using a derivatized gas chromatography-mass spectroscopy method. Exhaust gas was sampled from pre-GPF and post-GPF locations to determine the performance of the GPF regarding acid conversion. Lean and stoichiometric engine modes were considered with non-oxygenated gasoline and 10% splash blended ethanol in gasoline (E10) to examine the impact of stoichiometry and fuel type. Acid emissions represented as much as 0.51% of total unburned hydrocarbon emissions for total monocarboxylic acids and as much as 0.40% for total dicarboxylic acids. Individual acid concentrations were as high as 38 mg/kg-fuel for monocarboxylic acids and as high as 29 mg/kg-fuel for dicarboxylic acids. Overall, the study found that fuel oxygenates had mixed impact on the acid emissions. Engine-out monocarboxylic acids were reduced when using the E10 fuel by approximately 30–45% for the stoichiometric condition and increased marginally for the lean condition. Dicarboxylic acid emissions were generally insensitive to ethanol content. However, the engine condition significantly affected the acid emissions. Lean operation produced a factor of two to an order of magnitude higher emissions rates of both monocarboxylic and dicarboxylic acids than the stoichiometric condition. The catalytic GPF eliminated between 80 and 92% of the acids emitted from the engine, allowing some acids to be emitted into the environment.

42 ENGINEERING↗
DOE OSTI2023

THE IMPACT OF OXIDATION-INDUCED DEGRADATION ON MATERIALS USED IN HYDROGEN-FIRED MICROTURBINES

Hydrogen-fueled microturbines are being considered as part of the future green microgrid. However, the use of hydrogen as a fuel presents new challenges for selection and development of suitable high temperature materials for hydrogen combustion. The burning of hydrogen is expected to result in higher operating temperatures and higher than typically observed water vapor contents in exhaust gases than after burning natural gas. In the present work, foil specimens of various Fe- and Ni-based alloys were oxidized in air + 10vol.% H2O and air + 60vol.% H2O for up to 5,000 h at 700 °C to simulate the exhaust atmosphere of natural gas and hydrogen-fueled microturbines. The impact of alloy composition and water vapor content on the oxidation/ volatilization induced loss of wall thickness was experimentally evaluated. Enhanced external oxidation and volatilization of Cr¬2O3 and Ti-doped Cr2O3 scales was observed in 60 % H2O compared to 10% H2O. No significant impact of the higher water vapor content was observed on Al2O3 scales formed on Fe-based alumina forming alloys. Lifetime modeling was employed to predict the combined effects of water vapor content, gas flow rates, temperature and alloy composition on the oxidation-induced lifetime of the investigated materials

Romedenne, Marie↗
DOE OSTI2022

Effects of Synthesis Gas Concentration, Composition, and Operational Time on Tubular Solid Oxide Fuel Cell Performance

There is tremendous potential to utilize the exhaust gases and heat already present within combustion chambers to generate electrical power via solid oxide fuel cells (SOFCs). Variations in system design have been investigated as well as thorough examinations into the impacts of environmental conditions and fuel composition/concentration on SOFC performance. In an attempt to isolate the impacts of carbon monoxide and hydrogen concentration ratios within the exhaust stream, this work utilizes multi-temperature performance analyses with simulated methane combustion exhaust as fuel combined with dilute hydrogen baseline tests. These comparisons reveal the impacts of the complex reaction pathways carbon monoxide participates in when used as an SOFC fuel. Despite these complexities, performance reductions as a result of the presence of carbon monoxide are low when compared to similarly dilute hydrogen as a fuel. This provides further motivation for the continued development of SOFC-CHP systems. Stability testing performed over 80 h reveals the need for careful control of the operating environment as well as signs of carbon deposition. As a result of gas flow disruption, impacts of anode oxidation that may normally not hinder power production become significant factors in addition to coarsening of the anode material. Thermal management and strategies to minimize these impacts are a topic of future research.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Ability of Particulate Matter Index to describe sooting tendency of various gasoline formulations in a stratified-charge spark-ignition engine

This study investigates the ability of Particulate Matter Index (PMI) to describe the sooting behavior of various gasoline formulations in a stratified-charge (SC) spark-ignition engine. Specifically, the engine was operated at 2000 rpm with an intake pressure of 130 kPa where soot formation is known to primarily occur in the bulk gases. Exhaust soot emissions were measured for nine test fuels at various exhaust gas recirculation levels. A comparison between measured soot levels and PMI shows that PMI is a relatively poor predictor of the sooting tendency of the tested fuels under lean SC combustion. Among the fuels, three fuels, namely the diisobutylene blend, High Olefin, and E30 fuels exhibit measured soot behavior opposite of that predicted by PMI. Optical diagnostics were utilized to further investigate the in-cylinder phenomena for these three fuels. Analysis of natural luminosity and diffused back-illumination extinction imaging suggests that fuel-induced differences in the amount of soot formed are responsible for a majority of the discrepancy in measured versus predicted sooting tendency. Fuel-induced differences in soot oxidation and spray development seem to play minor roles. Because the combustion and air-fuel mixing processes for lean SC combustion are different from conventional stoichiometric operation it is hypothesized that the PMI correlation needs to be modified to account for differences in stoichiometric air-fuel ratio and level of oxygenation between fuels. Furthermore, the role of fuel volatility in PMI possibly needs to be de-emphasized for SC operation with fuel injection into compression-heated gases.

42 ENGINEERING↗
DOE OSTI2020

DIGITAL APPLICATIONS USING REAL-TIME VEHICLE EXHAUST INFORMATION

Vehicle emission is a major source of air pollution that causes a significant number of deaths globally. It has a profound impact on energy and the environment as well. The existing vehicle emission monitoring system is unable to help mitigating the pollution properly and therefore, requires precise real-time pollution measurement. The purpose of this paper is to discuss novel applications using the real-time measurement of pollutants from a vehicle tailpipe where exhaust gases enter the environment. Today, it is possible to measure such emission due to the emergence of affordable digital technologies such as the Internet of Things (IoT), wireless connectivity, cloud platform, and artificial intelligence. This paper discusses how digital technologies can be used for real-time monitoring of NOx gas as a measure of vehicle emission and predictive analytics applications. A description of data collection and pre-processing methodologies, actual collected data, and an approach to identify patterns between inputs such as vehicle speed and altitude and output such as NOx emission are included. Applying a simple neural network has produced promising results and is a first step towards developing predictive applications.

Digital, Vehicle Exhaust, IoT, AI, 1.4.2, Predicti↗
DOE OSTI2017

A numerical investigation on methane combustion and emissions from a natural gas-diesel dual fuel engine using CFD model

Natural gas (NG)-diesel dual fuel engines have been criticized for their high emissions of unburned methane. The past research on methane emissions from dual fuel engines has focused on the measurement of methane concentration in exhaust gases. The development of approaches capable of minimizing methane emissions requests the detailed spatial distribution of methane in-cylinder during the combustion and post combustion processes. However, it is difficult to experimentally measure the spatial distribution of methane in-cylinder. Here this research presents a numerical study on the combustion process of a NG-diesel dual fuel engine using the computational fluids dynamics (CFD) model CONVERGE coupled with a reduced primary reference fuel (PRF) mechanism. The model was validated against the heat release process and the emissions of nitrogen oxide, methane and carbon monoxide measured in a single cylinder dual fuel engine. The validated CFD model was applied to investigate the combustion of methane and n-heptane and the spatial distribution of methane in the dual fuel engine. This is most likely the first attempt to visualize the spatial distribution of methane in dual fuel engines using CFD. The objective of this study is to numerically simulate the methane combustion process, especially the methane present outside the pilot spray, quantify the methane combustion in each combustion stage, and visualize the spatial methane distribution in cylinder. The results showed that the momentum produced by the pilot fuel injection and combustion pushed the combustion products of pilot fuel and methane within the pilot spray plume toward the unburned methane-air mixture. Such a movement enhanced the mixing of the hot combustion products and the relatively cold unburned methane-air mixture during the main combustion process and dominated the combustion of methane presented outside the pilot fuel spray plume. Based on the simulation results at a low load condition (4.05 bar), the main combustion process consumed 43–53% of the methane fumigated into the intake mixture. The post-combustion oxidation process consumed 17–29% of the intake methane, which was 36.2–51.8% methane that survived the main combustion process. In comparison, 27–35% methane emitted the engine without participating the combustion process. The unburned methane at exhaust valve opening was mainly observed at the center of the cylinder. In comparison, the contribution of the crevice and boundary layer around the cylinder liner to methane emissions was relatively small. The slip of methane through the dual fuel engines was due to the fact that the premixed mixture was too lean to support the propagation of the turbulent flame initiated by the pilot fuel and the lack of pilot fuel vapor reaching the center of the combustion chamber because of the geometric limitations of the fuel injection system and the reduced mass of pilot fuel injected into the cylinder. The approaches aiming to enhance the combustion of methane and minimize methane emissions from dual fuel engines should focus on those capable of increasing the volume of pilot fuel vapor formed after injected into the cylinder.

42 ENGINEERING↗