Because phosphorus adversely affects exhaust catalysts, the EPA limits phosphorus in all gasolines to 0.0013g P/L.
As well as the above, there are various restrictions introduced by the Clean Air Act and state bodies such as California's Air Resources Board (CARB) that often have more stringent limits for the above properties, as well as additional limits. More detailed descriptions of the complex regulations can be found elsewhere [16,41,42] - I've just included some of the major changes, as some properties are determined by levels of permitted emissions, eg the toxics reduction required for fuel that has the maximim permitted benzene (1.0%), means total aromatics are limited to around 27%. There have been some changes in early 1996 to the implementation timetable, and the following timetable has not yet been changed.
The Clean Air Act also specifies some regions that exceed air quality standards have to use reformulated gasolines (RFGs) all year, starting January 1995. Other regions are required to use oxygenated gasolines for four winter months, beginning November 1992. The RFGs also contain oxygenates. Metropolitan regions with severe ozone air quality problems must use reformulated gasolines in 1995 that;- contain at least 2.0 wt% oxygen, reduce 1990 volatile organic carbon compounds by 15%, and reduce specified toxic emissions by 15% (1995) and 25% (2000). Metropolitan regions that exceeded carbon monoxide limits were required to use gasolines with 2.7 wt% oxygen during winter months, starting in 1992.
The 1990 Clean Air Act (CAA) amendments and CARB Phase 2 (1996) specifications for reformulated gasoline establish the following limits, compared with typical 1990 gasoline. Because of a lack of data, the EPA were unable to define the CAA required parameters, so they instituted a two-stage system. The first stage, the "Simple Model" is an interim stage that run from 1/Jan/1995 to 31/Dec/1997. The second stage, the "Complex Model" has two phases, Phase I (1995-1999) and Phase II (2000+), and there are different limits for EPA Control Region 1 (south) and Control Region 2 (north). Each refiner must have their RFG recertified to the Complex model prior to the 1/Jan/1998 implementation date. The following are some of the criteria for RFG when complying on a per gallon basis, more details are available elsewhere, including the details of the baseline fuel compositions to be used for testing [16,41,42,43].
1990 Clean Air Act CARB Simple Complex Phase 2 I II Limit Average benzene (max.vol.%) 2 1.00 1.00 1.00 1.00 0.8 oxygen (min.mass %) 0.2 2.0 2.0 2.0 1.8 - (max.mass %) - 2.7 - - 2.2 - sulfur (max.mass ppm) 150 no increase - - 40 30 aromatics (max.vol.%) 32 toxics reduction - - 25 22 olefins (max.vol.%) 9.9 no increase - - 6.0 4.0 reid vapour pressure (kPa) 60 55.8 (north) - - 48.3 - (during VOC Control Period) 49.6 (south) 50% evaporated (max.C) - - - - 98.9 93 90% evaporated (max.C) 170 - - - 148.9 143 VOC Reductions - Region I (min.%) 35.1 27.5 - - (VOC Control Period only) - Region II (min.%) 15.6 25.9 - - NOx Reductions - VOC Control Period (min.%) 0 5.5 - - - Non-VOC Control Period (min.%) 0 0 - - Toxics Reductions (min.%) 15.0 20.0 - -These regulations also specify emissions criteria. eg CAA specifies no increase in nitric oxides (NOx) emissions, reductions in VOC by 15% during the ozone season, and specified toxins by 15% all year. These criteria indirectly establish vapour pressure and composition limits that refiners have to meet. Note that the EPA also can issue CAA Section 211 waivers that allow refiners to choose which oxygenates they use. In 1981, the EPA also decided that fuels with up to 2% weight of oxygen ( from alcohols and ethers (except methanol)) were "substantially similar" to 1974 unleaded gasoline, and thus were not "new" gasoline additives. That level was increased to 2.7 wt% in 1991. Some other oxygenates have also been granted waivers, eg ethanol to 10% volume ( approximately 3.5 wt% ) in 1979 and 1982, and tert-butyl alcohol to 3.5 wt% in 1981. In 1987 and 1988 further waivers were issued for mixture of alcohols representing 3.7% wt of oxygen.
Texaco demonstrated that a well-formulated package could improve fuel economy, reduce NOx emissions, and restore engine performance because, as well as the traditional liquid-phase deposit removal, some additives can work in the vapour phase to remove existing engine deposits without adversely affecting performance ( as happens when water is poured into a running engine to remove carbon deposits :-) ). Chevron have also published data on the effectiveness of their additives , and successfully litigated to get Texoco to modify some of their claims . Most suppliers of quality gasolines will formulate similar additives into their products, and cheaper product lines are less like to have such additives added. As different brands of gasoline use different additives and oxygenates, it is probable that important fuel parameters, such as octane distribution, are slightly different, even though the pump octane ratings are the same.
So, if you know your car is well-tuned, and in good condition, but the driveability is pathetic on the correct octane, try another brand. Remember that the composition will change with the season, so if you lose driveability, try yet another brand. As various Clean Air Act changes are introduced over the next few years, gasoline will continue to change.
It is important to note that "oxygenated gasolines" have a hydrocarbon fraction that is not too different to traditional gasolines, but that the hydrocarbon fraction of "reformulated gasolines" ( which also contain oxygenates ) are significantly different to traditional gasolines.
The last 10 years of various compositional changes to gasolines for environmental and health reasons have resulted in fuels that do not follow historical rules, and the regulations mapped out for the next decade also ensure the composition will remain in a state of flux. The reformulated gasoline specifications, especially the 1/Jan/1998 Complex model, will probably introduce major reductions in the distillation range, as well as changing the various limits on composition and emissions.
I'm not going to list all 500+ HCs in gasolines, but the following are representative of the various classes typically present in a gasoline. The numbers after each chemical are:- Research Blending Octane : Motor Blending Octane : Boiling Point (C): Density (g/ml @ 15C) : Minimum Autoignition Temperature (C). It is important to realise that the Blending Octanes are derived from a 20% mix of the HC with a 60:40 iC8:nC7 ( 60 Octane Number ) base fuel, and the extrapolation of this 20% to 100%. These numbers result from API Project 45, and are readily available. As modern refinery streams have higher base octanes, these Blending Octanes are higher than those typically used in modern refineries. For example, modern Blending Octane ratings can be much lower ( toluene = 111RON and 94MON, 2-methyl-2-butene = 113RON and 81MON ), but detailed compilations are difficult to obtain.
The technique for obtaining Blending Octanes is different from rating the pure fuel, which often requires adjustment of the test engine conditions outside the acceptable limits of the rating methods. Generally, the actual octanes of the pure fuel are similar for the alkanes, but are up to 30 octane numbers lower than the API Project 45 Blending Octanes for the aromatics and olefins .
A traditional composition I have dreamed up would be like the following, whereas newer oxygenated fuels reduce the aromatics and olefins, narrow the boiling range, and add oxygenates up to about 12-15% to provide the octane. The amount of aromatics in super unleaded fuels will vary greatly from country to country, depending on the configuration of the oil refineries and the use of oxygenates as octane enhancers. The US is reducing the levels of aromatics to 25% or lower for environmental and human health reasons.
Some countries are increasing the level of aromatics to 50% or higher in super unleaded grades, usually to avoid refinery reconfiguration costs or the introduction of oxygenates as they phase out the toxic lead octane enhancers. An upper limit is usually placed on the amount of benzene permitted, as it is known human carcinogen.
15% n-paraffins RON MON BP d AIT n-butane 113 : 114 : -0.5: gas : 370 n-pentane 62 : 66 : 35 : 0.626 : 260 n-hexane 19 : 22 : 69 : 0.659 : 225 n-heptane (0:0 by definition) 0 : 0 : 98 : 0.684 : 225 n-octane -18 : -16 : 126 : 0.703 : 220 ( you would not want to have the following alkanes in gasoline, so you would never blend kerosine with gasoline ) n-decane -41 : -38 : 174 : 0.730 : 210 n-dodecane -88 : -90 : 216 : 0.750 : 204 n-tetradecane -90 : -99 : 253 : 0.763 : 200 30% iso-paraffins 2-methylpropane 122 : 120 : -12 : gas : 460 2-methylbutane 100 : 104 : 28 : 0.620 : 420 2-methylpentane 82 : 78 : 62 : 0.653 : 306 3-methylpentane 86 : 80 : 64 : 0.664 : - 2-methylhexane 40 : 42 : 90 : 0.679 : 3-methylhexane 56 : 57 : 91 : 0.687 : 2,2-dimethylpentane 89 : 93 : 79 : 0.674 : 2,2,3-trimethylbutane 112 : 112 : 81 : 0.690 : 420 2,2,4-trimethylpentane 100 : 100 : 98 : 0.692 : 415 ( 100:100 by definition ) 12% cycloparaffins cyclopentane 141 : 141 : 50 : 0.751 : 380 methylcyclopentane 107 : 99 : 72 : 0.749 : cyclohexane 110 : 97 : 81 : 0.779 : 245 methylcyclohexane 104 : 84 : 101 : 0.770 : 250 35% aromatics benzene 98 : 91 : 80 : 0.874 : 560 toluene 124 : 112 : 111 : 0.867 : 480 ethyl benzene 124 : 107 : 136 : 0.867 : 430 meta-xylene 162 : 124 : 138 : 0.868 : 463 para-xylene 155 : 126 : 138 : 0.866 : 530 ortho-xylene 126 : 102 : 144 : 0.870 : 530 3-ethyltoluene 162 : 138 : 158 : 0.865 : 1,3,5-trimethylbenzene 170 : 136 : 163 : 0.864 : 1,2,4-trimethylbenzene 148 : 124 : 168 : 0.889 : 8% olefins 2-pentene 154 : 138 : 37 : 0.649 : 2-methylbutene-2 176 : 140 : 36 : 0.662 : 2-methylpentene-2 159 : 148 : 67 : 0.690 : cyclopentene 171 : 126 : 44 : 0.774 : ( the following olefins are not present in significant amounts in gasoline, but have some of the highest blending octanes ) 1-methylcyclopentene 184 : 146 : 75 : 0.780 : 1,3 cyclopentadiene 218 : 149 : 42 : 0.805 : dicyclopentadiene 229 : 167 : 170 : 1.071 :Oxygenates Published octane values vary a lot because the rating conditions are significantly different to standard conditions, for example the API Project 45 numbers used above for the hydrocarbons, reported in 1957, gave MTBE blending RON as 148 and MON as 146, however that was partly based on the lead response, whereas today we use MTBE in place of lead.
methanol 133 : 105 : 65 : 0.796 : 385 ethanol 129 : 102 : 78 : 0.794 : 365 iso propyl alcohol 118 : 98 : 82 : 0.790 : 399 methyl tertiary butyl ether 116 : 103 : 55 : 0.745 : ethyl tertiary butyl ether 118 : 102 : 72 : 0.745 : tertiary amyl methyl ether 111 : 98 : 86 : 0.776 :There are some other properties of oxygenates that have to be considered when they are going to be used as fuels, particularly their ability to form very volatile azeotropes that cause the fuel's vapour pressure to increase, the chemical nature of the emissions, and their tendency to separate into a separate water-oxygenate phase when water is present. The reformulated gasolines address these problems more successfully than the original oxygenated gasolines.
Before you rush out to make a highly aromatic or olefinic gasoline to produce a high octane fuel, remember they have other adverse properties, eg the aromatics attack elastomers, may generate smoke, and result in increased emissions of toxic benzene. The olefins are unstable ( besides smelling foul ) and form gums. The art of correctly formulating a gasoline that does not cause engines to knock apart, does not cause vapour lock in summer - but is easy to start in winter, does not form gums and deposits, burns cleanly without soot or residues, and does not dissolve or poison the car catalyst or owner, is based on knowledge of the gasoline composition.