Petrol is a complex mixture of refinery hydrocarbon streams, additives, and in many cases, oxygenated blending components.
The final composition must meet critical specifications and efficiency characteristics for optimal performance in a variety of engine and vehicle types and technologies.
Fuel composition and quality also have a direct impact on vehicular emissions, both evaporative and exhaust, which impact air quality, fuel efficiency, and greenhouse gas (GHG) emissions.
Oxygenates are organic compounds which contain one or more oxygen atoms. Oxygenates enhance octane and improve the combustion of other petrol components. Only two types of oxygenates are commonly used as petrol blending components: alcohols and ethers.
Oxygenates use in petrol goes back to the 1970s, when refiners sought to replace lead with less toxic octane boosters and increase petrol volumes. In fuel, the most commonly found oxygenates are: methanol (MeOH), ethanol (EtOH), methyl tertiary butyl ether (MTBE), ethyl tertiary butyl ether (ETBE), tertiary amyl methyl ether (TAME) and tert-amyl ethyl ether (TAEE).
| MTBE | ETBE | TAME | TAEE | DIPE | |
|---|---|---|---|---|---|
| CAS Number | 1634-04-04 | 637-92-3 | 0994-05-08 | 919-94-8 | 108-20-3 |
| Molecular mass | 88 | 102 | 102 | 116 | 102 |
| Oxygen, wt.% | 18.2 | 15.7 | 15.7 | 13.8 | 15.7 |
| Solubility in water, g/L @25ºC | 42 | 12 | 4.5 | 4.5 | 20 |
| Boiling point, °C | 55 | 72 | 86 | 102 | 68 |
| RVP* blending, kPa | 55 | 28 | 10 | 9 | 34 |
| Density, kg/L | 0.74 | 0.75 | 0.77 | 0.77 | 0.73 |
| Stoichiometric air/fuel ratio | 11.73 | 12.15 | 12.15 | 12.57 | 12.15 |
| Net Energy Density, MJ/L | 26 | 27 | 28 | 29 | 27 |
| RON, blending | 117 | 119 | 110 | 108 | 110 |
| MON, blending | 102 | 103 | 99 | 95 | 99 |
| MeOH | EtOH | IPA | TBA | IBA | nBA | |
|---|---|---|---|---|---|---|
| CAS Number | 67-56-1 | 64-17-5 | 67-63-0 | 75-65-0 | 78-83-1 | 71-36-3 |
| Molecular mass | 32 | 46 | 60 | 74 | 74 | 74 |
| Oxygen, wt.% | 50.0 | 34.8 | 26.7 | 21.6 | 21.6 | 21.6 |
| Boiling point, °C | 65 | 78 | 82 | 83 | 108 | 117 |
| Density, kg/L | 0.8 | 0.79 | 0.79 | 0.78 | 0.8 | 0.81 |
| Stoichiometric air/fuel ratio | 6.46 | 8.98 | 10.33 | 11.16 | 11.16 | 11.16 |
| Net Energy Density, MJ/L | 16 | 21 | 25 | 27 | 27 | 27 |
| RVP*, neat, kPa | 31.7 | 17.3 | 12.4 | 11.7 | 4.1 | 2.8 |
| RVP* blending, kPa | 414 | 117.3 | 96.6 | 60.7 | 34.5 | 44.2 |
| RON, blending | 133 | 130 | 121 | 109 | 105 | 94 |
| MON, blending | 99 | 96 | 96 | 93 | 92 | 81 |
