Philadelphia (PA) - Researchers at Temple University have created a $200 device which makes diesel engines look far more attractive. It is a fuel thinner which creates smaller droplets: When injected into a diesel engine they burn more efficiency. Studies show fuel economy increasing by 19% in regular automobiles while, at the same time, decreasing greenhouse gas emissions. A Mercedes-Benz 300D sedan saw a 19% increase in highway driving, from 32 mpg to 38 mpg. A 15% increase was seen in city driving. But, is another diesel additive really what we need?
The process involves passing the fuel through a very small device which puts a weak electric field around the fuel. It changes the viscosity, making it thinner. The droplets which are then injected are naturally smaller and burn more efficiently.
Additional research is finding ways to significantly reduce greenhouse gas emissions. Today's diesel engines typically achieve about a 90% efficiency in conversion using diesel catalytic converters. These do not remove greenhouse gases, but typically use unoxydized O2 in the exhaust to convert CO (Carbon Monoxide) to CO2, and HC (hydrocarbons) into H20 + CO2. This is the primary reason modern diesel engines do not produce the thick, black smoke seen in diesels even 10 years ago.
Background: Gasoline and diesel engines
What makes a diesel engine different from a gasoline engine? For starters, diesels are more efficient. And if scientists could ever figure out how to reduce their emissions rather significantly, we would all be driving diesel powered vehicles in very short order for that reason. Diesel fuel efficiency is achieving around 60% today, compared to about 35% for gasoline.
Gasoline engines receive a mixture of air and fuel, which is prepared in advance by the carburator or fuel injection system. It is sucked in mixed form into the cylinder, compressed and ignited with a spark. The burning fuel heats up and expands the air, forcing it to drive the piston down.
Gasoline engines (for most automobiles) are four-stroke engines with intake, compression, power and exhaust strokes, taking two complete revolutions per cylinder before they can provide power again. And like gasoline engines, most diesel engines are also four-stroke. However, their similarties in combustion end just about there.
A diesel engine operates at a much higher compression, meaning there is less air space in the cylinder when it's fully compressed. It is actually this higher compression that makes diesel engines work. The compression heats up the air so much that it is the heat itself which causes the fuel to ignite. However, diesel engines do not have premixed fuel, for if they did they would be igniting before reaching the top of the stroke, causing a lack of power and potential damage to the engine.
In a diesel engine, the fuel is injected directly into the cylinder as a fine mist spray where it immediately ignites. And, like a gasoline engine, it is the burning fuel and heated air which forces the cylinder down. However, because the air is super-heated already, and because everything is happening at higher compression (a greater oxygen ratio to fuel), it burns faster and more efficiently.
How does thinning fuel help?
Diesel is a very stable fuel. At room temperature, you can actually extinguish a cigarette in an open container of diesel fuel (do not try this). It requires a temperature of 125 degrees F before it begins to outgas, meaning the fuel will vaporize like water evaporating in a pond. Diesel also begins to gel around 40 degrees F, making it impossible to use in automobiles without anti-gelling additives.
Because of diesel's liquid properties, it is somewhat difficult to get it to spray out in fine enough droplets to have enough surface area to make the fuel burn completely. This is typically why you see large amounts of black smoke when someone is accelerating hard in a diesel. If the fuel could be thinned, the droplets sprayed out could be smaller. This would greatly increase the surface area of the same amount of fuel. It could burn more completely.
Several researchers worldwide are working on ways to improve efficiency in diesel engines. In 2006, a European racing team developed two prototype racers that were able to sustain an average speed in excess of 135 mph for 24 hrs, all the while getting 105 mpg in diesel fuel economy.
A term called hypermiling is also being coined in North America. It refers to add-on efforts to increase fuel economy in stock automobiles. Using only gasoline, Wayne Gerdes - who initially coined the phrase - was able to achieve 59 mpg in a Honda Accord. Though that mileage is impressive in a gasoline powered vehicle, if you read through some of the techniques used by hypermilers it's not for your everyday commute, whereas the diesel Volkswagen and Peugeot vehicles are.