1. Dataset Title: AIR POLLUTANT EMISSIONS FROM NATURAL GAS-FUELED PUMPJACK ENGINES IN THE UINTA BASIN 2. Name and contact information of PI: a. Name: Seth Lyman b. Institution: Bingham Research Center, Utah State University c. Address: 320 N Aggie Blvd, Vernal, Utah, 84078, United States d. Email: seth.lyman@usu.edu e. ORCiD ID: 0000-0001-8493-9522 3. Funding source (Agency, Grant Number) if applicable: Utah Division of Air Quality, Utah Legislature, Uintah Impact Mitigation Special Service District 4. Project summary, description or abstract: We measured a comprehensive suite of pollutants emitted from 58 natural gas-fueled pumpjack engines in Utah’s Uinta Basin between January and May 2021, with repeat measurements of five engines in January 2022. We documented the emissions composition of several makes and models of commonly used engines, including Ajax E42, E565, DP60, and DP80 engines; Arrow L795, C101, and C106 engines; and GM Vortec. 5. Brief description of collection and processing of data: See https://www.usu.edu/binghamresearch/files/reports/PJengineemissions_mar2022.pdf 6. Description of files (names, or if too numerous, number of files, file type(s):engines_finaldata.csv is a comma-separated values file that contains all the data. 7. Location of measurements: Uinta Basin, Utah. Exact locations, well names, and company names are anonymized to protect the competitiveness of the companies involved in the study. 8. Uncertainty, precision, and accuracy of measurements, if known: See https://www.usu.edu/binghamresearch/files/reports/PJengineemissions_mar2022.pdf 9. Quality assurance and quality control that have been applied: See https://www.usu.edu/binghamresearch/files/reports/PJengineemissions_mar2022.pdf 10. Known problems that limit datas use (quality control, sampling issues, etc.): Some carbonyl data may be an underestimate, as indicated in the dataset and described in See https://www.usu.edu/binghamresearch/files/reports/PJengineemissions_mar2022.pdf. 11. Notes about the data: a. Exhaust velocity was measured at the stack exit. All other physical and chemical properties of stack exhaust were measured at a distance of 0.3 to 1.2 m within the stack exit. b. O2, CO2, CO, H2O, stack temperature, stack dewpoint, stack pressure were measured with an Ecom J2KN Pro. CH4 was measured with an LGR FGGA. Alkanes, alkenes+acetylene, aromatics, and alcohols were all measured by collection in whole-air canisters and analysis in the lab by GC-GC-MS. Carbonyls were collected on DNPH cartridges and analyzed in the lab by HPLC. c. N.D. indicates that measured values were below instrument detection. Blank cells indicate that no valid data exists. In other words, and N.D. means we are confident the value was below detection, and blank means we have no idea what the value was. 12. Descriptions of parameters/variables --Sample number: arbitrary number to identify each sample. --Company: anonymized as A, B, or C. --Date and Time: date and time the sample collection started. --Date and Time: date and time the sample collection ended. --Duration: units of minutes. duration of sample collection. --Engine: make and model of the measured engine. --Engine rated power: units of horsepower. rated horsepower of the engine. --Engine speed: units of RPM. engine speed in rotations per minute, measured aurally. --Air-fuel ratio (lambda): unitless. the ratio of air to fuel during combustion, calculated using the Brettschneider Equation, from a paper written by Dr. Johannes Brettschneider, at Robert Bosch in 1979 and published in “Bosch technische Berichte”, Vol 6 (1979) N0. 4, Pgs 177-186.. --Stack diam: units of m. diameter of the stack at the exit. --Stack height: units of m. height of the stack at exit. --Stack orient.: orientation of the stack at exit, H for horizontal, V for vertical. --Stack temp: units of C. temperature of the stack exhaust gas. --Stack dewpt.: units of C. dewpoint of the stack exhaust gas. --Stack pressure: units of mbar. pressure of the stack exhaust gas. --Stack exit veloc.: units of m/sec. exhaust exit velocity. --Stack flow Rate: units of m3/min volumetric. exhaust volumetric flow rate. --Stack flow Rate RPM*displac: units of m3/min volumetric. exhaust volumetric flow rate estimated by multiplying engine displacement by RPMS. --Stack Std. Flow Rate: units of m3/min @25C. exhaust flow rate at standard conditions of 25C and 1 atmosphere. --O2: units of mole fraction. mole fraction of the indicated chemical in the exhaust gas. --N2: units of mole fraction. mole fraction of the indicated chemical in the exhaust gas. 17.19:1 is the fuel-air mass ratio for air:methane (https://x-engineer.org/automotive-engineering/internal-combustion-engines/performance/air-fuel-ratio-lambda-engine-performance/), but we are wanting volume ratio, since the N2% here is % by volume. density of air is 1184 g/m3 at std conditions, while density of methane is 656 at same conditions. so we multiply 17.19 by 656 and 1 by 1184, and we get a ratio of 11277:1184, or 9.52:1. so the equation is N2% = 78.09-100*((78.09/100)*((1/9.52)/[excess air ratio])). 78.09 is the % N2 in air. The air-fuel mixture contains a stoichiometric ratio, plus any exess air, which is measured by the ecom, so we divide the fuel:air volumetric ratio by excess air, since this gives us the amount of actual fuel in the mixture. Then we multiply by the % N2 in air.. --Ar: units of mole fraction. mole fraction of the indicated chemical in the exhaust gas. Calculated by multiplying the amount of N2 by the Ar to N2 ratio in air, 0.93/78.09. . --CO2: units of mole fraction. mole fraction of the indicated chemical in the exhaust gas. --CO: units of mole fraction. mole fraction of the indicated chemical in the exhaust gas. --CH4: units of mole fraction. mole fraction of the indicated chemical in the exhaust gas. --NMOC: units of mole fraction. mole fraction of the indicated chemical in the exhaust gas. --H2O: units of mole fraction. mole fraction of the indicated chemical in the exhaust gas. --total acctd for: units of mole fraction. total mole fraction of the exhaust gas that was accounted for. --AmbientTemp: units of Deg C. Ambient air temperature. --Amb RH: units of %. Ambient air relative humidity. --Amb Dewpt: units of Deg C. Ambient air dewpoint. --Amb Press: units of mbar. Ambient air pressure. --Wind speed: units of meters/second. Ambient wind speed. --Wind Dir: units of Degrees. Ambient wind direction. --Latitude: units of deg. latitude of the measurement trailer (de-anonymized dataset only). --Longitude: units of deg. longitude of the measurement trailer (de-anonymized dataset only). --Altitude: units of Altitude (m). altitude of the measurement trailer (de-anonymized dataset only). --CO2: units of g/hr. emission rate of the indicated compound or compound group. --CO: units of g/hr. emission rate of the indicated compound or compound group. --NO: units of g/hr. emission rate of the indicated compound or compound group. --NO2: units of g/hr. emission rate of the indicated compound or compound group. --NOx: units of g/hr. emission rate of the indicated compound or compound group. --NOx: units of g/hp-hr. emission rate of NOx divided by the rated horsepower of the engine, determined from measurements. --NOx engineering eqtn.: units of g/hp-hr. emission rate of NOx divided by the rated horsepower of the engine, calculated using the percent O2 and ppm NOx in the equation available on page 25 of http://sgirt.webfactional.com/filesearch/content/Air%20Quality%20Division/Programs/Compliance/Inspections-Inspection%20Documents/AQD_Inspections_Revised-Protocol.pdf.. --CH4: units of g/hr. emission rate of the indicated compound or compound group. --TNMHC (no Alcohols): units of g/hr. emission rate of the indicated compound or compound group. --Alkanes: units of g/hr. emission rate of the indicated compound or compound group. --Alkenes: units of g/hr. emission rate of the indicated compound or compound group. --Aromatics: units of g/hr. emission rate of the indicated compound or compound group. --Alcohols: units of g/hr. emission rate of the indicated compound or compound group. --Carbonyls: units of g/hr. emission rate of the indicated compound or compound group. --Ethane: units of g/hr. emission rate of the indicated compound or compound group. --Ethylene: units of g/hr. emission rate of the indicated compound or compound group. --Propane: units of g/hr. emission rate of the indicated compound or compound group. --Propylene: units of g/hr. emission rate of the indicated compound or compound group. --Iso-butane: units of g/hr. emission rate of the indicated compound or compound group. --N-butane: units of g/hr. emission rate of the indicated compound or compound group. --Acetylene: units of g/hr. emission rate of the indicated compound or compound group. --Trans-2-Butene: units of g/hr. emission rate of the indicated compound or compound group. --1-Butene: units of g/hr. emission rate of the indicated compound or compound group. --Cis-2-butene: units of g/hr. emission rate of the indicated compound or compound group. --isopentane: units of g/hr. emission rate of the indicated compound or compound group. --n-pentane: units of g/hr. emission rate of the indicated compound or compound group. --trans-2-pentene: units of g/hr. emission rate of the indicated compound or compound group. --1-pentene: units of g/hr. emission rate of the indicated compound or compound group. --cis-2-pentene: units of g/hr. emission rate of the indicated compound or compound group. --2,2-dimethylbutane: units of g/hr. emission rate of the indicated compound or compound group. --cyclopentane/2,3-dimethylbutane: units of g/hr. emission rate of the indicated compound or compound group. --2-methylpentane: units of g/hr. emission rate of the indicated compound or compound group. --3-methylpentane: units of g/hr. emission rate of the indicated compound or compound group. --Isoprene: units of g/hr. emission rate of the indicated compound or compound group. --1-Hexene: units of g/hr. emission rate of the indicated compound or compound group. --n-Hexane: units of g/hr. emission rate of the indicated compound or compound group. --Methylcyclopentane/2,4-dimethylpentane: units of g/hr. emission rate of the indicated compound or compound group. --Benzene: units of g/hr. emission rate of the indicated compound or compound group. --Cyclohexane: units of g/hr. emission rate of the indicated compound or compound group. --2-Methylhexane: units of g/hr. emission rate of the indicated compound or compound group. --2,3-Dimethylpentane: units of g/hr. emission rate of the indicated compound or compound group. --3-Methylhexane: units of g/hr. emission rate of the indicated compound or compound group. --2,2,4-Trimethylpentane: units of g/hr. emission rate of the indicated compound or compound group. --n-Heptane: units of g/hr. emission rate of the indicated compound or compound group. --Methylcyclohexane: units of g/hr. emission rate of the indicated compound or compound group. --2,3,4-Trimethylpentane: units of g/hr. emission rate of the indicated compound or compound group. --Toluene: units of g/hr. emission rate of the indicated compound or compound group. --2-Methylheptane: units of g/hr. emission rate of the indicated compound or compound group. --3-Methylheptane: units of g/hr. emission rate of the indicated compound or compound group. --n-Octane: units of g/hr. emission rate of the indicated compound or compound group. --Ethylbenzene: units of g/hr. emission rate of the indicated compound or compound group. --m/p-Xylene: units of g/hr. emission rate of the indicated compound or compound group. --Styrene: units of g/hr. emission rate of the indicated compound or compound group. --o-Xylene: units of g/hr. emission rate of the indicated compound or compound group. --n-Nonane: units of g/hr. emission rate of the indicated compound or compound group. --Isopropylbenzene: units of g/hr. emission rate of the indicated compound or compound group. --n-Propbylbenzene: units of g/hr. emission rate of the indicated compound or compound group. --m-Ethyltoluene: units of g/hr. emission rate of the indicated compound or compound group. --p-Ethyltoluene: units of g/hr. emission rate of the indicated compound or compound group. --1,3,5-Trimethylbenzene: units of g/hr. emission rate of the indicated compound or compound group. --o-Ethyltoluene: units of g/hr. emission rate of the indicated compound or compound group. --1,2,4-Trimethylbenzene: units of g/hr. emission rate of the indicated compound or compound group. --n-Decane: units of g/hr. emission rate of the indicated compound or compound group. --1,2,3-Trimethylbenzene: units of g/hr. emission rate of the indicated compound or compound group. --m-Diethylbenzene: units of g/hr. emission rate of the indicated compound or compound group. --p-Diethylbenzene: units of g/hr. emission rate of the indicated compound or compound group. --n-Undecane: units of g/hr. emission rate of the indicated compound or compound group. --n-Dodecane: units of g/hr. emission rate of the indicated compound or compound group. --Methanol: units of g/hr. emission rate of the indicated compound or compound group. --Ethanol: units of g/hr. emission rate of the indicated compound or compound group. --Isopropanol: units of g/hr. emission rate of the indicated compound or compound group. --formaldehyde: units of g/hr. emission rate of the indicated compound or compound group. --acetaldehyde: units of g/hr. emission rate of the indicated compound or compound group. --acrolein: units of g/hr. emission rate of the indicated compound or compound group. --acetone: units of g/hr. emission rate of the indicated compound or compound group. --propionalehyde: units of g/hr. emission rate of the indicated compound or compound group. --crotonaldehyde: units of g/hr. emission rate of the indicated compound or compound group. --2-butanone (MEK): units of g/hr. emission rate of the indicated compound or compound group. --methacrolein: units of g/hr. emission rate of the indicated compound or compound group. --butyraldehyde: units of g/hr. emission rate of the indicated compound or compound group. --benzaldehyde: units of g/hr. emission rate of the indicated compound or compound group. --valeraldehyde: units of g/hr. emission rate of the indicated compound or compound group. --tolualdehydes: units of g/hr. emission rate of the indicated compound or compound group. --hexaldehyde: units of g/hr. emission rate of the indicated compound or compound group. --CO2: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --CO: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --NO: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --NO2: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --NOx: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --CH4: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --Ethane: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --Ethylene: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --Propane: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --Propylene: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --Iso-butane: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --N-butane: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --Acetylene: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --Trans-2-Butene: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --1-Butene: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --Cis-2-butene: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --isopentane: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --n-pentane: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --trans-2-pentene: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --1-pentene: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --cis-2-pentene: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --2,2-dimethylbutane: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --cyclopentane/2,3-dimethylbutane: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --2-methylpentane: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --3-methylpentane: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --Isoprene: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --1-Hexene: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --n-Hexane: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --Methylcyclopentane/2,4-dimethylpentane: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --Benzene: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --Cyclohexane: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --2-Methylhexane: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --2,3-Dimethylpentane: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --3-Methylhexane: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --2,2,4-Trimethylpentane: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --n-Heptane: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --Methylcyclohexane: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --2,3,4-Trimethylpentane: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --Toluene: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --2-Methylheptane: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --3-Methylheptane: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --n-Octane: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --Ethylbenzene: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --m/p-Xylene: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --Styrene: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --o-Xylene: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --n-Nonane: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --Isopropylbenzene: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --n-Propbylbenzene: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --m-Ethyltoluene: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --p-Ethyltoluene: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --1,3,5-Trimethylbenzene: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --o-Ethyltoluene: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --1,2,4-Trimethylbenzene: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --n-Decane: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --1,2,3-Trimethylbenzene: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --m-Diethylbenzene: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --p-Diethylbenzene: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --n-Undecane: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --n-Dodecane: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --Methanol: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --Ethanol: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --Isopropanol: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --formaldehyde: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --acetaldehyde: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --acrolein: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --acetone: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --propionalehyde: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --crotonaldehyde: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --2-butanone (MEK): units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --methacrolein: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --butyraldehyde: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --benzaldehyde: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --valeraldehyde: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --tolualdehydes: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --hexaldehyde: units of ppm. concentration of the indicated compound or compound group in the exhaust gas. --Are carbonyls the lower limit?: For some samples, the DNPH cartridges used to collect carbonyls became saturated with carbonyls during sampling. This means that additional carbonyls existed in exhaust gas that were not captured by our method. If this was the case, this variable will say "yes." If the data are not compromised in this way, this variable will say "no.". --Stack description: description of the exhaust stack. --Notes: any notes of interest. --CH4: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --Ethane: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --Ethylene: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --Propane: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --Propylene: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --Iso-butane: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --N-butane: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --Acetylene: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --Trans-2-Butene: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --1-Butene: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --Cis-2-butene: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --isopentane: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --n-pentane: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --trans-2-pentene: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --1-pentene: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --cis-2-pentene: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --2,2-dimethylbutane: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --cyclopentane/2,3-dimethylbutane: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --2-methylpentane: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --3-methylpentane: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --Isoprene: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --1-Hexene: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --n-Hexane: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --Methylcyclopentane/2,4-dimethylpentane: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --Benzene: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --Cyclohexane: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --2-Methylhexane: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --2,3-Dimethylpentane: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --3-Methylhexane: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --2,2,4-Trimethylpentane: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --n-Heptane: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --Methylcyclohexane: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --2,3,4-Trimethylpentane: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --Toluene: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --2-Methylheptane: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --3-Methylheptane: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --n-Octane: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --Ethylbenzene: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --m/p-Xylene: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --Styrene: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --o-Xylene: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --n-Nonane: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --Isopropylbenzene: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --n-Propbylbenzene: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --m-Ethyltoluene: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --p-Ethyltoluene: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --1,3,5-Trimethylbenzene: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --o-Ethyltoluene: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --1,2,4-Trimethylbenzene: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --n-Decane: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --1,2,3-Trimethylbenzene: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --m-Diethylbenzene: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --p-Diethylbenzene: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --n-Undecane: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --n-Dodecane: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --Methanol: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --Ethanol: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine. --Isopropanol: units of fuel gas composition (fraction). fraction of the indicated compound in the natural gas used as fuel by the engine.