During the oil embargo, regular unleaded gasoline prices jumped 57 percent and routine gasoline shortages also occurred. These events, and the regulation of many air pollutants, sparked a renewed interest in fuel efficiency, electric vehicles, and renewable fuels such as ethanol, which were seen as ways to meet the new regulations and reduce petroleum consumption. Today, the majority of ethanol in the United States is blended with gasoline to produce E10 10 percent ethanol, 90 percent gasoline.
Over 95 percent of gasoline sold in the United States is E In addition to having lower lifecycle greenhouse gas emissions than conventional gasoline, ethanol is an excellent octane provider, with neat pure ethanol having an octane rating of over Ethanol, which is generally the cheapest octane provider, is then used to bring the octane rating of the gasoline up to the labelled octane value on the gas pump.
For example, 84 octane gasoline is typically blended with 10 percent ethanol to reach the minimum octane requirement of 87 for retail gasoline. Currently, there are two ways of increasing the octane content of gasoline: increasing the volume of gasoline aromatics or increasing the volume of ethanol. While ethanol has a higher volatility than gasoline, meaning it vaporizes more quickly, it is a cleaner-burning alternative to petroleum-based octane boosters.
Additionally, the toxicity of ethanol is low compared to the health effects of BTEX and its combustion products, such as ultrafine particulates UFPs and polycyclic aromatic hydrocarbons PAHs.
A modest increase of ethanol content in fuel from 10 to 15 percent would result in an anticipated 6. There is contradictory evidence that increasing ethanol content in gasoline increases nitrous oxide NOX emissions, an ozone precursor. Several studies find either no relationship between ethanol blending and NOX emissions, or find decreased NOX emissions with increasing ethanol volumes.
Other studies suggest older cars emit more NOX when using ethanol blends. However, a study of make and model year vehicles found no increase in NOX emissions between E10, E15 and E20 blends, suggesting that both engine design and engine age play a role in NOX emissions. Overall, the effect of ethanol on NOX and carbon monoxide CO emissions is minor in newer engine emission control systems. RFS sets a minimum volume of renewable biofuels to be blended into the transportation fuel supply.
Final renewable fuel volumes for are This includes the categories of renewable fuels, cellulosic biofuels, advanced biofuels and biomass-based diesel. Lead and various petroleum products have provided octane to gasoline for over years, but evolving health and environmental concerns have led policymakers to reconsider the widespread use of many of these compounds.
As the United States looks to reduce the greenhouse gas intensity of the transportation sector, increasing the octane value of gasoline is a promising avenue, as it would enable more fuel-efficient engines.
But the health and environmental impacts of the octane sources that are used must be considered as well. A national transition to an optimized mid-level ethanol blend, between E25 25 percent ethanol, 75 percent gasoline and E40 40 percent ethanol , would lower consumer fuel costs and standardize the fuel supply. Leone, T. Olin, J.
Anderson, H. Jung, et al. Kalghatgi, G. Warrendale: Society of Automotive Engineers. Gibbs, L. Anderson, K. Barnes, et al. Motor Gasolines Technical Review. Chevron Corporation. Thomas, J. West, and S. Oak Ridge National Laboratory. Prakash, A. Octane Response of Premium-Recommended Vehicles.
SAE Technical Paper , doi Cracknell, V. Natarajan, D. Doyle et al. A similar undesirable condition is called pre-ignition, when the fuel ignites on its own before the spark ignites it.
Modern engine computers minimize this condition by controlling the timing of valves and fuel injection; however, this control mechanism can also come with a fuel-efficiency or emissions penalty. The standard means of testing octane is with an octane testing engine.
This test is similar to the way the mass of an object can be determined by comparing it to objects references of known mass on a balance scale. Primary Reference Fuels PRF of precisely known octane are formed by combining iso-octane, heptane, and other well-known standards such as toluene. These PRFs are used to bracket a given fuel sample to determine the pressure at which similar knock intensities are observed.
To determine the RON, the fuel is tested under engine idle conditions with a low air temperature and slow engine speed. To determine the MON the fuel is tested under the more stressful conditions of higher air temperature and engine speed.
Current designs see image below allow the same engine to perform both tests. Despite this flexibility, many testers still prefer to use more than one machine with each specifically set up and calibrated to perform either RON or MON tests.
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Compress it just a little and it ignites spontaneously. Octane handles compression very well -- you can compress it a lot and nothing happens. It spontaneously ignites at a given compression level, and can only be used in engines that do not exceed that compression ratio. Cheaper grades of gasoline could be made usable by adding TEL. This led to the widespread use of "ethyl" or "leaded" gasoline. Unfortunately, the side effects of adding lead to gasoline are:. When lead was banned, gasoline got more expensive because refineries could not boost the octane ratings of cheaper grades any more.
Airplanes are still allowed to use leaded gasoline known as AvGas , and octane ratings of or more are commonly used in super-high-performance piston airplane engines. In the case of AvGas, is the gasoline's performance rating, not the percentage of actual octane in the gas. The addition of TEL boosts the compression level of the gasoline -- it doesn't add more octane. Currently engineers are trying to develop airplane engines that can use unleaded gasoline.
Jet engines burn kerosene , by the way. Sign up for our Newsletter!
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