Gasoline FAQ


    5.5.1) Emission Standards

There are several bodies responsible for establishing standards, and they promulgate test cycles, analysis procedures, and the % of new vehicles that must comply each year. The test cycles and procedures do change ( usually indicated by an anomalous increase in the numbers in the table ), and I have not listed the percentages of the vehicle fleet that are required to comply. This table is only intended to convey where we have been, and where we are going. It does not cover any regulation in detail - readers are advised to refer to the relevant regulations. Additional limits for other pollutants, such as formaldehyde (0.015g/mi.) and particulates (0.08g/mi), are omitted. The 1994 tests signal the federal transition from 50,000 to 100,000 mile compliance testing, and I have not listed the subsequent 50,000 mile limits [28,76,77].

Year                    Federal                      California
                HCs    CO    NOx    Evap       HCs    CO    NOx    Evap
               g/mi   g/mi  g/mi   g/test     g/mi   g/mi  g/mi   g/test
Before regs   10.6   84.0   4.1    47        10.6   84.0   4.1    47
add crankcase +4.1                           +4.1
1966                                          6.3   51.0   6.0
1968           6.3   51.0   6.0
1970           4.1   34.0                     4.1   34.0           6
1971           4.1   34.0           6(CC)     4.1   34.0   4.0     6
1972           3.0   28.0           2         2.9   34.0   3.0     2
1973           3.0   28.0   3.0               2.9   34.0   3.0     2
1974           3.0   28.0   3.0               2.9   34.0   2.0     2
1975           1.5   15.0   3.1     2         0.90   9.0   2.0     2
1977           1.5   15.0   2.0     2         0.41   9.0   1.5     2
1980           0.41   7.0   2.0     6(SHED)   0.41   9.0   1.0     2
1981           0.41   3.4   1.0     2         0.39   7.0   0.7     2
1993           0.41   3.4   1.0     2         0.25   3.4   0.4     2
1994  50,000   0.26   3.4   0.3     2   TLEV  0.13   3.4   0.4     2
1994 100,000   0.31   4.2   0.6     2
1997                                    LEV   0.08   3.4   0.2
1997                                    ULEV  0.04   1.7   0.2
1998                                    ZEV   0.0    0.0   0.0     0
2004           0.125  1.8   0.16    2<>
It's also worth noting that exhaust catalysts also emit platinum, and the soluble platinum salts are some of the most potent sensitizers known. Early research [78] reported the presence of 10% water-soluble platinum in the emissions, however later work on monolithic catalysts has determined the quantities of water soluble platinum emissions are negligible [79]. The particle size of the emissions has also been determined, and the emissions have been correlated with increasing vehicle speed. Increasing speed also increases the exhaust gas temperature and velocity, indicating the emissions are probably a consequence of physical attrition.

           Estimated Fuel                           Median Aerodynamic
Speed       Consumption         Emissions           Particle Diameter
km/h          l/100km            ng/m-3                    um
60              7                  3.3                     5.1           
100             8                 11.9                     4.2
140            10                 39.0                     5.6
US Cycle-75                        6.4                     8.5<>
Using the estimated fuel consumption, and about 10m3 of exhaust gas per litre of gasoline, the emissions are 2-40 ng/km. These are 2-3 orders of magnitude lower than earlier reported work on pelletised catalysts. These emissions may be controlled directly in the future. They are currently indirectly controlled by the cost of platinum, and the new requirement for the catalyst to have an operational life of at least 100,000 miles.

  5.6) Why do exhaust catalysts influence fuel composition?

Modern adaptive learning engine management systems control the combustion stoichiometry by monitoring various ambient and engine parameters, including exhaust gas recirculation rates, the air flow sensor, and exhaust oxygen sensor outputs, This closed loop system using the oxygen sensor can compensate for changes in fuel content and air density. The oxygen sensor is also known as the lambda sensor because the actual air-fuel mass ratio divided by the stoichiometric air-fuel mass ratio is known as lambda or the air-fuel equivalence ratio.

The preferred technique for describing mixture strength is the fuel-air equivalence ratio ( phi ), which is the actual fuel-air mass ratio divided by the stoichiometric fuel-air mass ratio, however most enthusiasts use air-fuel ratio and lambda. Lambda is the inverse of the fuel-air equivalence ratio. The oxygen sensor effectively measures lambda around the stoichiometric mixture point. Typical stoichiometric air-fuel ratios are [80]:

      6.4  methanol
      9.0  ethanol
     11.7  MTBE
     12.1  ETBE, TAME
     14.6  gasoline without oxygenates<>
The engine management system rapidly switches the stoichiometry between slightly rich and slightly lean, except under wide open throttle conditions - when the system runs open loop. The response of the oxygen sensor to composition changes is about 3 ms, and closed loop switching is typically 1-3 times a second, going between 50mV ( lambda = 1.05 (Lean)) to 900mV (lambda = 0.99 ( Rich)). The catalyst oxidises about 80% of the H2, CO, and HCs, and reduces the NOx [76].

Typical reactions that occur in a modern 3-way catalyst are:

2H2 + O2 -> 2H2O
2CO + O2 -> 2CO2
CxHy + (x + (y/4))O2 -> xCO2 + (y/2)H2O
2CO + 2NO -> N2 + 2CO2
CxHy + 2(x + (y/4))NO -> (x + (y/4))N2 + (y/2)H2O + xCO2
2H2 + 2NO -> N2 + 2H2O
CO + H20 -> CO2 + H2
CxHy + xH2O -> xCO + (x + (y/2))H2
The use of exhaust catalysts have resulted in reaction pathways that can accidentally be responsible for increased pollution. An example is the CARB-mandated reduction of fuel sulfur. A change from 450ppm to 50ppm, which will reduce HC & CO emissions by 20%, was shown to increase formaldehyde by 45%, but testing in later model cars did not exhibit the same effect [32,58, 59]. This demonstrates that continuing changes to engine management systems can also change the response to fuel composition changes.

The requirement that the exhaust catalysts must now endure for 10 years or 100,000 miles will also encourage automakers to push for lower levels of elements that affect exhaust catalyst performance, such as sulfur and phosphorus, in both the gasoline and lubricant. Modern catalysts are unable to reduce the relatively high levels of NOx that are produced during lean operation down to approved levels, thus preventing the application of lean-burn engine technology. Recently Mazda has announced they have developed a "lean burn" catalyst, which may enable automakers to move the fuel combustion towards the lean side, and different gasoline properties may be required to optimise the combustion and reduce pollution [81]. Mazda claim that fuel efficiency is improved by 5-8%, while meeting all emission regulations, and some Japanese manufacturers have evaluated lean-burn catalysts in limited numbers of 1995 production models.

Catalysts also inhibit the selection of gasoline octane-improving and cleanliness additives ( such as MMT and phosphorus-containing additives ) that may result in refractory compounds known to physically coat the catalyst, reducing available catalyst and thus increasing pollution.

  5.7) Why are "cold start" emissions so important?

The catalyst requires heat to reach the temperature ( >300-350C ) where it functions most efficiently, and the delay until it reaches operating temperature can produce more hydrocarbons than would be produced during the remainder of many typical urban short trips. It has been estimated that 70-80% of the non-methane HCs that escape conversion by the catalysts are emitted during the first two minutes after a cold start. As exhaust emissions have been reduced, the significance of the evaporative emissions increases. Several engineering techniques are being developed, including the Ford Exhaust Gas Igniter ( uses a flame to heat the catalyst - lots of potential problems ), zeolite hydrocarbon traps, and relocation of the catalyst closer to the engine [76].

Reduced gasoline volatility and composition changes, along with cleanliness additives and engine management systems, can help minimise cold start emissions, but currently the most effective technique appears to be rapid, deliberate heating of the catalyst, and the new generation of low thermal inertia "fast light-up" catalysts reduce the problem, but further research is necessary [76,82].

As the evaporative emissions are also starting to be reduced, the emphasis has shifted to the refuelling emissions. These will be mainly controlled on the vehicle, and larger canisters may be used to trap the vapours emitted during refuelling.

  5.8) When will the emissions be "clean enough"?

The California ZEV regulations effectively preclude IC vehicles, because they stipulate zero emissions. However, the concept of regulatory forcing of alternative vehicle propulsion technology may have to be modified to include hybrid or fuel-cell vehicles, as the major failing of EVs remains the lack of a cheap, light, safe, and easily-rechargeable electrical storage device [83,84]. There are several major projects intending to further reduce emissions from automobiles, mainly focusing on vehicle mass and engine fuel efficiency, but gasoline specifications and alternative fuels are also being investigated. It may be that changes to IC engines and gasolines will enable the IC engine to continue well into the 21st century as the prime motive force for personal transportation [77,85]. There have also been calls to use market forces to reduce pollution from automobiles [86], however most such suggestions ( increased gasoline taxes, congestion tolls, and emission-based registration fees ) are currently considered politically unacceptable. The issue of how to target the specific "gross polluters" is being considered, and is described in Section 5.14.

  5.9) Why are only some gasoline compounds restricted?

The less volatile hydrocarbons in gasoline are not released in significant quantities during normal use, and the more volatile alkanes are considerably less toxic than many other chemicals encountered daily. The newer gasoline additives also have potentially undesirable properties before they are even combusted. Most hydrocarbons are very insoluble in water, with the lower aromatics being the most soluble, however the addition of oxygen to hydrocarbons significantly increases the mutual solubility with water.

                      Compound in Water            Water in Compound       
                      % mass/mass @  C             % mass/mass @  C
normal decane            0.0000052  25               0.0072      25
iso-octane               0.00024    25               0.0055      20
normal hexane            0.00125    25               0.0111      20
cyclohexane              0.0055     25               0.010       20
1-hexene                 0.00697    25               0.0477      30
toluene                  0.0515     25               0.0334      25
benzene                  0.1791     25               0.0635      25
methanol                complete    25              complete     25
ethanol                 complete    25              complete     25 
MTBE                     4.8        20               1.4         20
TAME                      -                          0.6         20
The concentrations and ratios of benzene, toluene, ethyl benzene, and xylenes ( BTEX ) in water are often used to monitor groundwater contamination from gasoline storage tanks or pipelines. The oxygenates and other new additives may increase the extent of water and soil pollution by acting as co-solvents for HCs.

Various government bodies ( EPA, OSHA, NIOSH ) are charged with ensuring people are not exposed to unacceptable chemical hazards, and maintain ongoing research into the toxicity of liquid gasoline contact, water and soil pollution, evaporative emissions, and tailpipe emissions [87]. As toxicity is found, the quantities in gasoline of the specific chemical ( benzene ), or family of chemicals ( alkyl leads, aromatics, olefins ) are regulated.

The recent dramatic changes caused by the need to reduce alkyl leads, halogens, olefins, and aromatics has resulted in whole new families of compounds ( ethers, alcohols ) being introduced into fuels without prior detailed toxicity studies being completed. If adverse results appear, these compounds are also likely to be regulated to protect people and the environment.

Also, as the chemistry of emissions is unravelled, the chemical precursors to toxic tailpipe emissions ( such as higher aromatics that produce benzene emissions ) are also controlled, even if they are not themselves toxic.

  5.10) What does "renewable" fuel or oxygenate mean?

The general definition of "renewable" is that the carbon originates from recent biomass, and thus does not contribute to the increased CO2 emissions. A truly "long-term" view could claim that fossil fuels are "renewable" on a 100 million year timescale :-). There was a major battle between the ethanol/ETBE lobby ( agricultural, corn growing ), and the methanol/MTBE lobby ( oil company, petrochemical ) over an EPA mandate demanding that a specific percentage of the oxygenates in gasoline are produced from "renewable" sources [88]. On 28 April 1995 a Federal appeals court permanently voided the EPA ruling requiring "renewable" oxygenates, thus fossil-fuel derived oxygenates such as MTBE are acceptable oxygenates [89].

Unfortunately, "renewable" ethanol is not cost competitive when crude oil is $18/bbl, so a federal subsidy ( $0.54/US Gallon ) and additional state subsidies ( 11 states - from $0.08(Michigan) to $0.66(Tenn.)/US Gal.) are provided. Ethanol, and ETBE derived from ethanol, are still likely to be used in states where subsidies make them competitive with other oxygenates.

  5.11) Will oxygenated gasoline damage my vehicle?

The following comments assume that your vehicle was designed to operate on unleaded, if not, then damage such as exhaust valve seat recession may occur. Damage should not occur if the gasoline is correctly formulated, and you select the appropriate octane, but oxygenated gasoline will hurt your pocket. In the first year of mandated oxygenates, it appears some refiners did not carefully formulate their oxygenated gasoline, and driveability and emissions problems occurred. Most reputable brands are now carefully formulated. Some older activated carbon canisters may not function efficiently with oxygenated gasolines, but this is a function of the type of carbon used. How your vehicle responds to oxygenated gasoline depends on the engine management system and state of tune. A modern system will automatically compensate for all of the currently-permitted oxygenate levels, thus your fuel consumption will increase. Older, poorly-maintained, engines may require a tune up to maintain acceptable driveability.

Be prepared to try several different brands of oxygenated or reformulated gasolines to identify the most suitable brand for your vehicle, and be prepared to change again with the seasons. This is because the refiners can choose the oxygenate they use to meet the regulations, and may choose to set some fuel properties, such as volatility, differently to their competitors.

Most stories of corrosion etc, are derived from anhydrous methanol corrosion of light metals (aluminum, magnesium), however the addition of either 0.5% water to pure methanol, or corrosion inhibitors to methanol-gasoline blends will prevent this. If you observe corrosion, talk to your gasoline supplier. Oxygenated fuels may either swell or shrink some elastomers on older cars, depending on the aromatic and olefin content of the fuels. Cars later than 1990 should not experience compatibility problems, and cars later than 1994 should not experience driveability problems, but they will experience increased fuel consumption, depending on the state of tune and engine management system.

  5.12) What does "reactivity" of emissions mean?

the traditional method of exhaust regulations was to specify the actual HC, CO, NOx, and particulate contents. With the introduction of oxygenates and reformulated gasolines, the volatile organic carbon (VOC) species in the exhaust also changed. The "reactivity" refers to the ozone-forming potential of the VOC emissions when they react with NOx, and is being introduced as a regulatory means of ensuring that automobile emissions do actually reduce smog formation. The ozone-forming potential of chemicals is defined as the number of molecules of ozone formed per VOC carbon atom, and this is called the Incremental Reactivity. Typical values ( big is bad :-) ) are [74]:

Maximum Incremental Reactivities as mg Ozone / mg VOC

                  carbon monoxide           0.054
alkanes           methane                   0.0148
                  ethane                    0.25
                  propane                   0.48
                  n-butane                  1.02
olefins           ethylene                  7.29
                  propylene                 9.40
                  1,3 butadiene            10.89
aromatics         benzene                   0.42
                  toluene                   2.73
                  meta-xylene               8.15      
                  1,3,5-trimethyl benzene  10.12
oxygenates        methanol                  0.56
                  ethanol                   1.34
                  MTBE                      0.62
                  ETBE                      1.98<>

  5.13) What are "carbonyl" compounds?

Carbonyls are produced in large amounts under lean operating conditions, especially when oxygenated fuels are used. Most carbonyls are toxic, and the carboxylic acids can corrode metals. The emission of carbonyls can be controlled by combustion stoichiometry and exhaust catalysts, refer to section 5.5 for typical reductions for aldehydes. Typical carbonyls are:

  5.14) What are "gross polluters"?

It has always been known that the EPA emissions tests do not reflect real world conditions. There have been several attempts to identify vehicles on the road that do not comply with emissions standards. Recent remote sensing surveys have demonstrated that the highest 10% of CO emitters produce over 50% of the pollution, and the same ratio applies for the HC emitters - which may not be the same vehicles [91-102]. 20% of the CO emitters are responsible for 80% of the CO emissions, consequently modifying gasoline composition is only one aspect of pollution reduction. The new additives can help maintain engine condition, but they can not compensate for out-of-tune, worn, or tampered-with engines.

The most famous of these remote sensing systems is the FEAT ( Fuel Efficiency Automobile Test ) team from the University of Denver [99]. This team is probably the world leader in remote sensing of auto emissions to identify grossly polluting vehicles. The system measures CO/CO2 ratio, and the HC/CO2 ratio in the exhaust of vehicles passing through an infra-red light beam crossing the road 25cm above the surface. The system also includes a video system that records the licence plate, date, time, calculated exhaust CO, CO2, and HC. The system is effective for traffic lanes up to 18 metres wide, however rain, snow, and water spray can cause scattering of the beam. Reference signals monitor such effects and, if possible, compensate. The system has been comprehensively validated, including using vehicles with on-board emissions monitoring instruments.

They can monitor up to 1000 vehicles an hour and, as an example,they were invited to Provo, Utah to monitor vehicles, and gross polluters would be offered free repairs [100]. They monitored over 10,000 vehicles and mailed 114 letters to owners of vehicles newer than 1965 that had demonstrated high CO levels. They received 52 responses and repairs started in Dec. 1991, and continued to Mar 1992.

 The entire monitored fleet at Provo (Utah) during Winter 1991:1992 
 Model year               Grams CO/gallon            Number of
                    (Median value) (mean value)      Vehicles
   92                    40             80              247
   91                    55                            1222
   90                    75                            1467
   89                    80                            1512
   88                    85                            1651
   87                    90                            1439
   86                   100            300             1563
   85                   120                            1575
   84                   125                            1206
   83                   145                             719
   82                   170                             639
   81                   230                             612
   80                   220            500              551
   79                   350                             667
   78                   420                             584
   77                   430                             430
   76                   770                             317
   75                   760            950              163
   Pre 75               920           1060              878<>
As observed elsewhere, over half the CO was emitted by about 10% of the vehicles. If the 47 worst polluting vehicles were removed, that achieves more than removing the 2,500 lowest emitting vehicles from the total tested fleet.

Surveys of vehicle populations have demonstrated that emissions systems had been tampered with on over 40% of the gross polluters, and an additional 20% had defective emission control equipment [101]. No matter what changes are made to gasoline, if owners "tune" their engines for power, then the majority of such "tuned" vehicle will become gross polluters. Professional repairs to gross polluters usually improves fuel consumption, resulting in a low cost to owners ( $32/pa/Ton CO year ). The removal of CO in the Provo example above was costed at $200/Ton CO, compared to Inspection and Maintenance programs ($780/Ton CO ), and oxygenates ( $1034-$1264/Ton CO in Colorado 1991-2 ), and UNOCALs vehicle scrapping programme ( $1025/Ton of all pollutants ).

Thus, identifying and repairing or removing gross polluters can be far more cost-effective than playing around with reformulated gasolines and oxygenates. A recent study has confirmed that gross polluters are not always older vehicles, and that vehicles have been scrapped that passed the 1993 new vehicle emission standards [102]. The study also confirmed that if estimated costs and benefits of various emission reduction strategies were applied to the tested fleet, the identification and repair techniques are the most cost-effective means of reducing HC and CO. It should be noted that some strategies ( such as the use of oxygenates to replace aromatics and alkyl lead compounds ) have other environmental benefits.

Action                      Vehicles   Estimated  % reduction  % reduction 
                            Affected     Cost                  per $billion
                           (millions) ($billion)   HC    CO     HC    CO
Reformulated Fuels            20         1.5       17    11     11     7.3
Scrap pre-1980 vehicles        3.2       2.2       33    42     15    19
Scrap pre-1988 vehicles       14.6      17         44    67      2.6   3.9
Repair worst 20% of vehicles   4         0.88      50    61     57     69
Repair worst 40% of vehicles   8         1.76      68    83     39     47

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