Energy content of fuels

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Gasoline contains, on average, 32 MJ/L. Actual energy content varies, by up to 4%, from season to season and from batch to batch[1]. On average, about 19.5 USgal of gasoline are available from a 42 USgal barrel of crude oil (about 46% by volume), varying due to quality of crude and grade of gasoline. The remaining residue comes off as products ranging from tar to naptha.[2]

Volumetric and mass energy density of some fuels compared with gasoline:[3]

Fuel type MJ/litre MJ/kg BTU/Imp gal BTU/USgal Research octane
number (RON)
87 Octane Gasoline 32.0 44.4[4] 150,100 125,000 Min 91Template:Clarify me
Autogas (LPG) (60% Propane + 40% Butane) 26.8 46 108
Ethanol 23.5 31.1[5] 101,600 84,600 129
Methanol 17.9 19.9 77,600 64,600 123
Butanol 29.2 36.6 91-99Template:Clarify me
Gasohol (10% ethanol + 90% gasoline) 31.2 145,200 120,900 93/94Template:Clarify me
Diesel(*) 38.6 45.4 166,600 138,700 25
Biodiesel 33.3-35.7 [6]Template:Clarify me
Aviation gasoline (high octane gasoline, not jet fuel) 33.5 46.8 144,400 120,200
Jet fuel (kerosene based) 35.1 43.8 151,242 125,935
Liquefied natural gas 25.3 55 109,000 90,800
Hydrogen 1-10Template:Clarify me 121 130[7]

(*) Diesel fuel is not used in a gasoline engine, so its low octane rating is not an issue; the relevant metric for diesel engines is the cetane number

A high octane fuel such as Liquefied petroleum gas (LPG) has a lower energy content than lower octane gasoline, resulting in an overall lower power output at the regular compression ratio an engine ran at on gasoline. However, with an engine tuned to the use of LPG (i.e. via higher compression ratios such as 12:1 instead of 8:1), this lower power output can be overcome. This is because higher-octane fuels allow for a higher compression ratio - this means less space in a cylinder on its combustion stroke, hence a higher cylinder temperature which improves efficiency according to Carnot's theorem, along with fewer wasted hydrocarbons (therefore less pollution and wasted energy), bringing higher power levels coupled with less pollution overall because of the greater efficiency.

The main reason for the lower energy content (per litre) of LPG in comparison to gasoline is that it has a lower density. Energy content per kilogram is higher than for gasoline (higher hydrogen to carbon ratio). The weight-density of gasoline is about 740 kg/m³ (6.175 lb/US gal; 7.416 lb/imp gal).

Different countries have some variation in what RON (Research Octane Number) is standard for gasoline, or petrol. In the UK, ordinary regular unleaded petrol is 91 RON (not commonly available), premium unleaded petrol is always 95 RON, and super unleaded is usually 97-98 RON. However both Shell and BP produce fuel at 102 RON for cars with hi-performance engines, and the supermarket chain Tesco began in 2006 to sell super unleaded petrol rated at 99 RON. In the US, octane ratings in unleaded fuels can vary between 86-87 AKI (91-92 RON) for regular, through 89-90 AKI (94-95 RON) for mid-grade (European Premium), up to 90-94 AKI (95-99 RON) for premium (European Super).

[edit] References

  1. EPA - Find actual citation[verification needed]
  2. Oil Industry Statistics from Gibson Consulting accessdate = 2008-07-31
  3. Appendix B, Transportation Energy Data Book from the Center for Transportation Analysis of the Oak Ridge National Laboratory
  4. Thomas, George: Overview of Storage Development DOE Hydrogen Program. Livermore, CA. Sandia National Laboratories. 2000.
  5. Calculated from heats of formation. Does not correspond exactly to the figure for MJ/l divided by density.
  6. Bioenergy Feedstock Development Programs at Oak Rodge National Laboratory
  7. National Hydrogen Association FAQs


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