Chemistry

Diesel Emissions Petroleum Diesel vs Biodiesel



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Whether you grew up on a farm or in the city, at one time or another we've all had an up close and personal experience with diesel. Providing economical, reliable power delivery, diesel has powered much of the freedom of movement common to daily living. The main complaint for most people has been noise and smelly exhaust.

All internal combustion engines take in fuel and air and burn it to perform work for us. Whether burning gasoline, diesel or even wood in your fireplace, a byproduct of the combustion is burned gases. Depending on the method of burning and the fuel used, these gases can be toxic. The familiar black smoke from diesel engines is called particulate matter (PM). Both the EPA and the state of California have identified diesel particulate matter as toxic.

Originally designed to operate on peanut oil or coal dust, the simple diesel engine design uses heat and pressure to burn fuel rather than spark ignition of gasoline engines. The simplicity and flexibility of the engine make it popular among heavy industry, transport and agricultural industries. Combined with low fuel oil prices of the early twentieth century, petroleum diesel became the fuel of choice, especially for non-consumer applications. Though petroleum has been preferred, diesels have always had the capacity to operate on alternative fuel.

Fuel prices have been the driving factor for petroleum diesel dominance, until now. Biodiesel is fuel which has been produced from a renewable resource. Among the benefits of biodiesel are the biodegradable characteristic making spills less of a concern, greater fuel ignitability and higher oxygen content. Biodiesel also reduces greenhouse gas (GHG) emissions in a couple of ways - 1) less carbon dioxide is produced through burning and 2) the plants grown to make the fuel absorb the carbon dioxide that is produced. Compared to regular diesel, unblended biodiesel (B100) offers a 75% reduction in CO2, blended biodiesel - 20% by volume (B20) offers a 15% reduction in CO2 according to a Department of Energy study. Biodiesel also is more "big picture" energy balance friendly generating more energy in use than is required for its production. Varieties of biodiesel made from soy, canola or animal fat have slightly different emissions characteristics. All of which out perform petroleum diesel.

Emissions are usually tested in one of three ways: an engine dynamometer, a chassis dynamometer, or through a portable system which is carried on board a vehicle. Biodiesel testing has been conducted using all of these methods with differing results. In general, increasing proportions of biodiesel introduced into the testing process results in decreasing proportions of harmful emissions.

Emissions consist of: oxides of nitrogen (NOx), particulate matter (PM), carbon monoxide (CO), volatile organic compounds (VOC) and sulfur dioxide (SO2) along with some other byproducts. Biodiesel testing has shown significant reductions in the emissions of all of these components with the possible exception of NOx which showed increases of up to 2%. There is debate about the accuracy of NOx testing which is under investigation now. This is a concern, but the overall emissions benefits of biodiesel are significant and grow proportionally to the amount of biodiesel in blended fuel.

During emissions testing, biodiesel blended in specific proportions is compared to emissions of petroleum diesel. B100, pure biodiesel and B20 a 20% biodiesel/80% petroleum diesel blend are the most common test fuels. B100 contains about 10% oxygen by weight offering a distinct advantage in combustion by allowing the fuel to burn more completely. Along with the reduced harmful gases, biodiesel PM has been shown to be less toxic than petroleum diesel PM. In the near term, Catalyst agent additives are being tested and introduced into biodiesel systems to reduce the bothersome NOx gases.

Imagine if you will for just a moment working in a dark, damp, underground mine environment where the air is never fresh. Mining equipment is largely powered by diesel engines. Heart and lung diseases have been linked to diesel PM, but now the air for breathing is becoming fresher since mining companies have begun to implement biodiesel fuel in their operations. Miners have fresher, less toxic air to breathe, and the mining companies benefit by saving money on air treatment and equipment modifications which would otherwise be required. There are drawbacks and adjustments to be made when using biodiesel, but off road applications like the mining example are where the real benefits from biodiesel use will be felt through improved air quality for everyone.

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