The hydrocarbon combustion reaction releases heat energy and is an example of an exothermic reaction. Below is a hydrocarbon combustion animation showing the net reaction that occurs when methane combines with oxygen.ĬH 4 + 2O 2 → CO 2 + 2H 2O Heat Energy ( Enthalpy) Methane releases its chemical energy by undergoing hydrocarbon combustion. However, this means that it is also a significant contributor to climate change since this methane produces a fair amount of the carbon dioxide that humans emit into the atmosphere.īelow is a table of some of the basic properties of methane. It can even provide energy for transportation. Methane combustion (see simulation at bottom of page) provides a significant fraction of the world's primary energy, and is used for home heating, cooking food, heating water, and electrical generation. It has a shorter atmospheric lifetime than CO 2, at 12 years, but this is "balanced" by the fact that it is more effective at trapping heat than CO 2, as methane has a GWP ( Global warming potential) of 21. Methane is also a greenhouse gas, like carbon dioxide (CO 2). Īt typical temperatures and pressures it is a gas and makes up around 95% of the content of liquefied natural gas, and around 80-90% of natural gas. Methane is the main hydrocarbon component of natural gas, which is a type of fossil fuel. As a hydrocarbon, it can undergo hydrocarbon combustion which gives off heat. Methane is an alkane with the chemical formula CH 4. Space filling model of methane the white spheres represent hydrogen atoms and the black spheres represent carbon atoms. If desired, the nonroad CO2 equivalent methane emissions may be estimated outside the model by multiplying the CH 4 output by its GWP.Figure 1. However, nitrous oxide and CO 2 equivalent are not modelled for nonroad equipment. Methane emissions are modeled as a function of total hydrocarbons. Nonroad atmospheric CO 2 is computed from BSFC in the same way as onroad CO 2 is computed from onroad fuel consumption. tons will depend on the units selected on the “General Output” panel. Whether this is grams, kilograms, pounds, or U.S. The input for this value is in lbs/bhp-hr, but engine population and activity are applied within MOVES, so MOVES outputs the total mass of fuel per day for the given engine category in the nation or selected county. The equation and GWP values used by MOVES to calculate CO 2 equivalent emissions are documented in Section 4.2 of the Greenhouse Gas and Energy Consumption Rates for Onroad Vehicles MOVES3.įor nonroad equipment, fuel consumption is modelled as “Brake Specific Fuel Consumption” (BSFC). For more information on GWPs, see EPA’s website, Understanding Global Warming Potentials. Note, these GWP values have not been updated recently. Nitrous oxide (N 2O) has a GWP value of 298. In MOVES:ĬO 2 has a GWP value of 1 (the reference). If selected, MOVES will estimate total "CO 2 equivalent" emissions for onroad vehicles by multiplying CH 4 and N 2O emissions by their global warming potential (GWP) and adding them to the atmospheric CO 2 estimate to calculate the CO 2 equivalent. MOVES does not estimate hydrofluorocarbon (HFC) emissions. In addition, MOVES models onroad vehicle emissions of methane (CH4) and nitrous oxide (N 2O), which also contribute to climate change. We refer to this CO 2 as "atmospheric" and calculate it based on the total carbon in the fuel. While small portion of the fuel used in the vehicle is initially released to the atmosphere as unburned fuel or as carbon monoxide (CO), we assume that eventually all of the released carbon will convert to CO 2 in the atmosphere (i.e., the “oxidation fraction” equals one). MOVES estimates only the direct emissions from the vehicle and does not model the upstream emissions or energy consumption from producing the fuel. The CO 2 equation used by MOVES and the carbon content of each fuel are documented in Section 4.1 of the Greenhouse Gas and Energy Consumption Rates for Onroad Vehicles MOVES3. Then using the fuel carbon content, MOVES calculates the CO 2 emitted from burning the fuel in the vehicle. MOVES calculates the energy it takes to operate an onroad vehicle based on energy consumption rates as explained in the technical reports Greenhouse Gas and Energy Consumption Rates for Onroad Vehicles MOVES3 (pdf) (November 2020, EPA-420-R-20-015) and Exhaust Emission Rates for Heavy-Duty Onroad Vehicles in MOVES3 (pdf) (November 2020, EPA-420-R-20-018). See More Frequent Questions about MOVES and Related Models.
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