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The performance and operational characteristics of autogas vehicles compare very favourably with other fuels. Autogas has a higher octane rating than gasoline so converted gasoline-powered spark-ignition engines tend to run more smoothly. This reduces engine wear and maintenance requirements, including less frequent spark plug and oil changes. Autogas exhibits less soot formation than both gasoline and diesel, reducing abrasion and chemical degradation of the engine oil. In addition, autogas does not dilute the lubricating film on the cylinder wall, which is a particular problem with gasoline engines in cold starts. The higher octane of autogas also allows higher compression ratios, which can deliver increased engine-power output and better thermal efficiency, reducing fuel consumption and emissions. Acceleration and top speed using the latest generation of autogas-fuel systems are comparable to gasoline or diesel. Autogas has a lower energy density than gasoline and diesel. Although this has no effect on engine performance, it does mean that a larger volume of fuel and a bigger tank are required to achieve the same overall driving range.
In practice, converting a vehicle to be able to run on autogas involves some relatively minor operational inconveniences. The most important of these are a loss of boot/trunk space to accommodate the fuel tank and, in some cases (depending on the equipment installed), a marginal loss in acceleration and speed mainly due to the extra weight of the tank. This is also a problem for CNG vehicles. The development of new technologies, including ring-tanks and lightweight composite tanks, has helped to alleviate these problems. This inconvenience is offset to some extent by the lower weight of autogas fuel compared to gasoline and the increased flexibility provided by the dual-fuel capability of converted vehicles. Practical experience has shown that vehicle owners are willing to convert their vehicles to autogas if the savings in running costs are sufficiently attractive.
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From an energy-security perspective, autogas demonstrates advantages over conventional fuels. There is an abundant supply of LP Gas from many sources around the world. In addition to proven reserves in oil and gas fields, the flexibility of modern refining processes offers considerable potential for expanding supply to meet demand from the transport sector. LP Gas supply is expected to rise briskly in the next few years with growing natural gas production and associated liquids extraction – already the primary source of LP Gas worldwide. And field and refinery supplies will also increase as wasteful flaring and venting practices, which are still common in many parts of the world, are eradicated. In addition, there is considerable scope for diverting supplies from relatively low-value petrochemical uses, where LP Gas can easily be replaced by other feedstocks such as naphtha, ethane and distillate. The use of gaseous automotive fuels may also enhance energy security in the long term, by paving the way for a hydrogen economy, where lessons learned in the handling and use of gas, storage, transportation and safety will be critically important areas.
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Autogas is an outstanding fuel for vehicles that must comply with increasingly stringent emission requirements. Low emissions of particulates (PM), carbon monoxide (CO), nitrogen oxides (NOx) and hydrocarbons (HC) enable autogas to outscore conventional fuels and most other alternative fuels for environmental benefits. It also plays an important role in mitigating climate change because it has among the lowest life-cycle greenhouse gas emissions of all commercially available fuels. Moreover, autogas is a non-toxic and non-poisonous fuel that will not contaminate aquifers or soil if spilled.
Autogas is a clean transportation fuel with impressive environmental benefits that offer an immediate, practical solution to improve air quality, especially in urban areas.
GAIN welcomes your contributions of recent studies comparing vehicle emissions.
* Autogas offers an immediate, concrete solution to improve air quality especially in urban areas. In terms of air-borne emissions of the principal regulated noxious gases, autogas is among the lowest of all automotive fuels available today. According to authoritative scientific testing, autogas yields 50% less carbon monoxide, 40% less hydrocarbons, 35% less nitrogen oxides, and 50% less ozone forming potential compared to gasoline. The health benefits from such lower emissions are significant.
* Autogas can play an important role in mitigating climate change. It has among the lowest greenhouse gas emissions of all commercially available fuels, when measured over its full life cycle. For example, autogas can produce on average 20% less CO2 equivalent compared to gasoline when total emissions from well to wheel are taken into consideration.
* The environmental advantages of autogas over conventional and other alternative fuels are even greater with respect to unregulated emissions, including air toxics. Compared to gasoline and diesel, autogas has lower VOC (volatile organic compounds), formaldehyde, acetaldehyde, butadiene, and benzene emissions. The analysis also shows that autogas therefore has the lowest impact on potential cancer risk.
* Autogas vehicles will maintain their environmental advantages compared to other conventional automotive fuels, especially regarding the current unregulated pollutants. Autogas will also benefit from new automotive technologies that optimise fuel combustion, such as direct injected gasoline and diesel vehicles.
* Autogas features far lower NOx and PM emissions compared with diesel vehicles, even those equipped with the most advanced technologies such as particulate traps or special diesel particulate filters.
* Congestion driving dynamics tend to increase emissions of CO, HC, PM and fuel consumption, mainly due to engine load changes or high engine loads. During these periods, catalysts do not perform at the optimal level - but these increases are far lower for autogas vehicles than for gasoline. Diesel cars show a significant increase of PM at high loads.
* Another positive characteristic of an autogas engine is the reduced emissions at cold engine start. (Note: Cold start emissions represent a significant percentage of a vehicle's total emissions. When an engine and the associated exhaust catalysts are cold, they do not perform effectively, enabling emissions to escape through the tailpipe). This phenomenon is particularly important for urban fleet vehicles operating on short trips.
* Autogas is an intrinsically clean fuel. It will demonstrate clean emissions over the lifetime of the vehicle, regardless of the owner or the existence and maintenance of exhaust gas after-treatment technologies (necessary for gasoline and diesel vehicles to achieve similar emissions performance). This was confirmed in a US Environmental Protection Agency study that demonstrated that OEM autogas vehicles show very little deterioration of emission performance during a vehicle's useful life (up to 120,000 miles).
* Finally, an added environmental benefit is that in the event of fuel spill, autogas quickly evaporates into the air. Therefore, in contrast to gasoline and diesel, there is never a risk of ground or water contamination. Moreover, autogas vehicles are significantly less noisy than diesel-powered light and heavy duty vehicles.
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