{"id":2481,"date":"2019-09-13T16:05:34","date_gmt":"2019-09-13T23:05:34","guid":{"rendered":"https:\/\/c21-wp.phas.ubc.ca\/?post_type=article&p=2481"},"modified":"2019-10-22T11:56:51","modified_gmt":"2019-10-22T18:56:51","slug":"fossil-fuels-for-transport","status":"publish","type":"article","link":"https:\/\/c21.phas.ubc.ca\/article\/fossil-fuels-for-transport\/","title":{"rendered":"Fossil Fuels for Transport"},"content":{"rendered":"
The three most common types of fossil fuel used for transportation are as follows:<\/p>\n
Although these fuels differ greatly in how they are used and handled, for the purposes of energy and GHG calculations, they are all more-or-less the same.<\/p>\n
Gasoline<\/strong> is the most common liquid fuel for internal combustion engines. Its chemical composition is complicated and variable, but a simple approximation removes all these uncertainties and allows to make sufficiently accurate energy and CO$_2$ production calculations.<\/p>\n The most important characteristics of gasoline for the purposes of our calculations are:<\/p>\n 1.<\/strong> Enthalpy of combustion (“energy content”) in terms of MJ\/kg and MJ\/L. These two quantities are linked via the density in kg\/L.<\/p>\n Engineering Toolbox[note]Engineering Toolbox https:\/\/www.engineeringtoolbox.com\/fuels-higher-calorific-values-d_169.html [2019-09-13][\/note] gives an enthalpy value of 46.4 MJ\/kg noting that this value may vary either way by 5-10%. The density of 737 kg\/m$^3$ (0.737 kg\/L) thus gives an enthalpy of 34.2 MJ\/L.<\/p>\n 2.<\/strong> Hydrogen to carbon ratio (H\/C): the three main components of gasoline are isooctane, butane and 3-ethyltoluene [note]Gasoline: chemical analysis and production, https:\/\/en.wikipedia.org\/wiki\/Gasoline#Chemical_analysis_and_production [2019-09-13][\/note], whose H\/C ratios are 18\/8, 12\/9 and 12\/5 respectively. In other words, H\/C $\\approx$ 2.<\/p>\n Using H\/C = 2, we can calculate the CO$_2$ production for a given quantity of fuel burned.<\/p>\n CH$_2$ + 3\/2 O$_2 \\rightarrow$ CO$_2$ + H$_2$O $\\tag{1}$<\/strong><\/p>\n Taking the molar masses of CH$_2$ to be 14 and CO$_2$ to be 44, this means that 14 kg of gasoline (14\/0.737 = 19.0 L) burns to 44 kg of CO$_2$. Thus 1 L<\/strong> of gasoline burns to 44\/14 = 2.3 kg of CO$_2$<\/strong>. This is the generally accepted value[note] “How much carbon dioxide is produced by burning gasoline and diesel fuel?”. U.S. Energy Information Administration (EIA). [2013-10-27][\/note], i.e. H\/C = 2 is a perfectly usable approximation.<\/p>\n Diesel<\/strong><\/p>\n Diesel fuel is a heavier fraction of crude oil and consists of a mixture of different hydrocarbons with an average chemical composition of C$_{12}$H$_{24}$[note]Diesel, chemical analysis, https:\/\/en.wikipedia.org\/wiki\/Diesel_fuel#Chemical_analysis [2019-09-16].[\/note]. Thus H\/C = 2 is as good an assumption as for gasoline, and CO$_2$ emissions in terms of kg\/kg will be the same.<\/p>\n The enthalpy of combustion is 45.6 MJ\/kg, 38.6 MJ\/L with a density of 846 kg\/m$^3$[note]Engineering Toolbox https:\/\/www.engineeringtoolbox.com\/fuels-higher-calorific-values-d_169.html [2019-09-13][\/note].<\/p>\n Jet Fuel<\/strong><\/p>\n Jet fuel, a.k.a. aviation kerosene or Jet-A, has a mean chemical composition of C$_{12}$H$_{26}$[note]Kerosene, https:\/\/en.wikipedia.org\/wiki\/Kerosene#Engines<\/a> [2019-09-16].[\/note], i.e. H\/C = 2.17 or a little larger than 2. The CO$_2$ emissions in terms of kg\/kg will be a few % less than for gasoline or diesel.<\/p>\n