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Diesel Boosted by Natural Gas
October 26, 2012   
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Researchers at the Lublin University of Technology in eastern Poland are working to build a diesel engine powered by a mixture of diesel fuel and compressed natural gas (CNG).

The researchers have received a zl.3 million government grant. The project is among 180 that were selected by the National Center for Research and Development from among more than 1,000 nationwide.

The Lublin researchers say they have solved the problem of putting CNG installations in diesel engines.

Prof. Mirosław Wendeker of the Lublin University of Technology’s Faculty of Mechanical Engineering says the project has explored how to dispense CNG fuel directly into the combustion chamber, thereby reducing diesel consumption, fuel cost and environmental impact.

Michał Biały, a Ph.D. student at the Lublin University of Technology who is also involved in the project, says the aim is to reduce consumption of diesel fuel. “Things should become cheaper and more ecological,” he says.

Compressed natural gas is cheaper than propane-butane, while being equally safe and more environmentally friendly. The main problem is that it requires special cylinders and filling stations.

CNG is a natural gas comprising more than 90 percent methane. When it is burned by the engine, 20 percent less carbon dioxide is produced than in the case of gasoline, and a vehicle powered exclusively by CNG makes half the noise of a vehicle powered by traditional fuel. For now, in Poland, few vehicles use CNG, unlike in Italy, for example, where this fuel is used by thousands of vehicles, including passenger cars.

In Poland there are only 33 filling stations where CNG is available; moreover, only 12 of them are open around the clock. This fuel is easiest to obtain in southern Poland, in cities such as Lublin, Wrocław and Wałbrzych. Among the major cities in central and northern Poland, CNG is only available in Radom, Warsaw, Toruń, Bydgoszcz, Olsztyn, Elbl±g, Gdynia, and Słupsk.

CNG cylinders are strong and safe, but they have two drawbacks: they are heavy and expensive. In the case of steel cylinders, each liter of capacity means about a kilogram of weight. Composite cylinders are significantly lighter, but far more expensive. A certified steel cylinder costs about 3.50 euros per liter of capacity. At the current exchange rate of the zloty against the euro, this means that a 50-liter cylinder will cost more than zl.700. It can accommodate almost 10 cubic meters of CNG, which in the case of a car fitted with a relatively powerful engine is only enough to travel 100 km.

Consequently, it is necessary to install five or six such cylinders in a car to enable it to travel a decent distance. And this means extra weight—around 300 kilograms.

In the case of cars fitted with a gasoline engine, putting in a CNG system is not significantly different, in terms of complexity, from the assembly of an LPG installation.

In the case of a diesel engine, the matter is more complicated. There are two main ways to adapt such engines to burn CNG. In one of these methods, it is necessary to create a spark ignition system, which in practice means turning a diesel engine into something along the lines of a gasoline engine. The other method is based on injecting a reduced dose of diesel fuel into the cylinder at the right time.

Currently, 80-by-20 installations are used most often. This means that 80 percent of the fuel burned by the engine is diesel and 20 percent is CNG. This means roughly 15 percent savings in terms of fuel costs.

The price of such an installation is high and in the case of trucks it may reach 30,000 euros. There are also installations that make it possible to change the proportions of diesel fuel and CNG burned. In their case, after the engine has warmed up, the ratio can be 80 percent CNG and 20 percent diesel fuel. The high costs of the installation make the investment profitable only in the case of diesel engines used in delivery vans and trucks.

Experiments with diesel engines and CNG have also been conducted by Prof. Andrzej Piętak at the University of Warmia and Mazury in the northeastern city of Olsztyn. In these experiments, Piętak determined the diesel and methane proportions needed for the engine to be economical and work smoothly. Piętak has also written a special computer program to control the engine’s fuel system. The program calculates the diesel fuel and gas combination on an ongoing basis depending on acceleration and load. Long-term research has shown that the use of CNG for powering a diesel engine does not change the parameters of the engine, but the ride is about 30 percent cheaper than in the case of a diesel engine powered exclusively by diesel fuel.

In his research Piętak also used bio-diesel—ethyl esters of rapeseed oil—instead of conventional diesel fuel. The exhaust gases in the case of bio-diesel are much cleaner than in the case of conventional diesel oil. The environmental impact is consequently much lower.
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