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4.12 Are brands different? Yes. The above specifications are intended to ensure minimal quality standards are maintained, however as well as the fuel hydrocarbons, the manufacturers add their own special ingredients to provide additional benefits. A quality gasoline additive package would include:- * octane-enhancing additives ( improve octane ratings ) * anti-oxidants ( inhibit gum formation, improve stability ) * metal deactivators ( inhibit gum formation, improve stability ) * deposit modifiers ( reduce deposits, spark-plug fouling and preignition ) * surfactants ( prevent icing, improve vaporisation, inhibit deposits, reduce NOx emissions ) * freezing point depressants ( prevent icing ) * corrosion inhibitors ( prevent gasoline corroding storage tanks ) * dyes ( product colour for safety or regulatory purposes ). During the 1980s significant problems with deposits accumulating on intake valve surfaces occurred as new fuel injection systems were introduced. These intake valve deposits (IVD) were different than the injector deposits, in part because the valve can reach 300C. Engine design changes that prevent deposits usually consist of ensuring the valve is flushed with liquid gasoline, and provision of adequate valve rotation. Gasoline factors that cause deposits are the presence of alcohols or olefins . Gasoline manufacturers now routinely use additives that prevent IVD and also maintain the cleanliness of injectors. These usually include a surfactant and light oil to maintain the wetting of important surfaces. Intake valve deposits have also been shown to have significant adverse effects on emissions , and deposit control additives will be required to both reduce emissions and provide clean engine operation . A slighty more detailed description of additives is provided in Section 9.1. 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 Texaco to modify some of their claims . Most suppliers of quality gasolines will formulate similar additives into their products, and cheaper product lines are less likely 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. 4.13 What is a typical composition? There seems to be a perception that all gasolines of one octane grade are chemically similar, and thus general rules can be promulgated about "energy content ", "flame speed", "combustion temperature" etc. etc.. Nothing is further from the truth. The behaviour of manufactured gasolines in octane rating engines can be predicted, using previous octane ratings of special blends intended to determine how a particular refinery stream responds to an octane-enhancing additive. Refiners can design and reconfigure refineries to efficiently produce a wide range of gasolines feedstocks, depending on market and regulatory requirements. There is a worldwide trend to move to unleaded gasolines, followed by the introduction of exhaust catalysts and sophisticated engine management systems. 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. 4.14 Is gasoline toxic or carcinogenic? There are several known toxins in gasoline, some of which are confirmed human carcinogens. The most famous of these toxins are lead and benzene, and both are regulated. The other aromatics and some toxic olefins are also controlled. Lead alkyls also require ethylene dibromide and/or ethylene dichloride scavengers to be added to the gasoline, both of which are suspected human carcinogens. In 1993 an International Symposium on the Health Effects of Gasoline was held . Major review papers on the carcinogenic, neurotoxic, reproductive and developmental toxicity of gasoline, additives, and oxygenates were presented, and interested readers should obtain the proceedings. The oxygenates are also being evaluated for carcinogenicity, and even ethanol and ETBE may be carcinogens. The introduction of oxygenated gasoline to Alaska and some other areas of the USA resulted in a range of complaints. Recent research has been unable to identify additional toxicity, but has detected increased levels of offensive smell . It should be noted that the oxygenated gasolines were not initially intended to reduce the toxicity of emissions. The reformulated gasolines will produce different emissions, and specific toxins must initially be reduced by 15% all year. The removal of alkyl lead compounds certainly reduces the toxicity of exhaust gas emissions when used on engines with modern engine management systems and 3-way exhaust catalysts. If unleaded gasolines are not accompanied by the introduction of catalysts, some other toxic emissions may increase. Engines without catalysts will produce increased levels of toxic carbonyls such as formaldehyde and acrolein when using oxygenated fuels, and increased levels of toxic benzene when using highly aromatic fuels. There is little doubt that gasoline is full of toxic chemicals, and should therefore be treated with respect. However the biggest danger remains the flammability, and the relative hazards should always be kept in perspective. The major toxic risk from gasolines comes from breathing the tailpipe, evaporative, and refuelling emissions, rather than occasional skin contact from spills. Breathing vapours and skin contact should always be minimised. 4.15 Is unleaded gasoline more toxic than leaded? The short answer is no. However that answer is not global, as some countries have replaced the lead compound octane-improvers with aromatic or olefin octane-improvers without introducing exhaust catalysts. The aromatics contents may increase to around 40%, with high octane unleaded fuels reaching 50% in countries where oxygenates are not being used, and the producers have not reconfigured refineries to produce high octane paraffins. In general, aromatics are significantly more toxic than paraffins. Exhaust catalysts have a limited operational life, and will be immediately poisoned if misfuelled with leaded fuel. Catalyst failure can result in higher levels of toxic emissions if catalysts or engine management systems are not replaced or repaired when defective. Maximum benefit of the switch to unleaded are obtained when the introduction of unleaded is accompanied by the introduction of exhaust catalysts and sophisticated engine management systems. Unfortunately, the manufacturers of alkyl lead compounds have embarked on a worldwide misinformation campaign in countries considering emulating the lead-free US. The use of lead precludes the use of exhaust catalysts, thus the emissions of aromatics are only slightly diminished, as leaded fuels typically contain around 30-40% aromatics. Other toxins and pollutants that are usually reduced by exhaust catalysts will be emitted at significantly higher levels if leaded fuels are used . The use of unleaded on modern vehicles with engine management systems and catalysts can reduce aromatic emissions to 10% of the level of vehicles without catalysts . Alkyl lead additives can only substitute for some of the aromatics in gasoline, consequently they do not eliminate aromatics, which will produce benzene emissions . Alkyl lead additives also require toxic organohalogen scavengers, which also react in the engine to form and emit other organohalogens, including highly toxic dioxin . Leaded fuels emit lead, organohalogens, and much higher levels of regulated toxins because they preclude the use of exhaust catalysts. In the USA the gasoline composition is being changed to reduce fuel toxins ( olefins, aromatics ) as well as emissions of specific toxins. 4.16 Is reformulated gasoline more toxic than unleaded? The evidence so far indicates that the components of reformulated gasolines ( RFGs ) are more benign than unleaded, and that the tailpipe emissions of hydrocarbons are significantly reduced for cars without catalysts, and slightly reduced for cars with catalysts and engine management systems. The emissions of toxic carbonyls such as formaldehyde, acetaldehyde and acrolein are increased slightly on all vehicles, and the emission of MTBE is increased about 10x on cars without catalysts and 4x on cars with catalysts . When all the emissions ( evaporative and tailpipe ) are considered, RFGs significantly reduce emissions of hydrocarbons, however the emissions of carbonyls and MTBE may increase . There has been an extensive series of reports on the emissions from RFGs, produced by the Auto/Oil Air Quality Improvement Research Program, who measured and calculated the likely effects of RFG [18,19,20,58,59,60,61]. More research is required before a definitive answer on toxicity is available. The major question about RFGs is not the toxicity of the emissions, but whether they actually meet their objective of reducing urban pollution. This is a more complex issue, and most experts agree the benefits will only be modest [18,19,20,61,62]. 4.17 Are all oxygenated gasolines also reformulated gasolines? No. Oxygenates were initially introduced as alternative octane-enhancers in the 1930s, and are still used in some countries for that purpose. In the US the original "oxygenated gasolines" usually had a slightly- modified gasoline as the hydrocarbon fraction. The US EPA also mandated their use to reduce pollution, mainly via the "enleanment" effect on engines without sophisticated management systems, but also because of the "aromatics substitution" effect. As vehicles with fuel injection and sophisticated engine management systems became pervasive, reformulated gasolines could be introduced to further reduce pollution. The hydrocarbon component of RFGs is significantly different to the hydrocarbon fraction in earlier oxygenated gasolines, having lower aromatics contents, reduced vapour pressure, and a narrower boiling range. RFGs do contain oxygenates as the octane-enhancer, but have different hydrocarbon composition profiles [34,41,42,43,44].