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Hvid Engine Combustion


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Americans saw a record high price of $70.85 per barrel of crude oil on Aug. 30 of this year, and since then, large truck and SUV sales have plummeted and hybrid car sales have soared. As of the end of September 2005, 154,563 hybrid vehicles were sold in the U.S., as compared to just 88,000 in the entire 2004 calendar year, an increase of over 175 percent.

Without a doubt, the quest for better fuel economy is stronger now than ever before. However, this quest began many years ago.

In 1915, Rasmus Hvid, inventor of the Hvid engine, sought to improve the fuel economy of stationary engines by creating an engine that would run on heavier, low-grade (i.e., cheaper) fuels such as kerosene, as opposed to gasoline or Diesel.

This invention, patented April 6, 1915, is what Hvid (pronounced "Veed") called an "Oil Injection Device for Oil Engines." It essentially worked on the principles of Rudolf Diesel's engine, but with a twist: The Hvid relied solely on the heating and compression of air to ignite the fuel, without the use of compressors, pumps, injectors, etc., to aid combustion.

The beauty of the Hvid engine lies in its simplicity, making it easier to produce, and thus, easier on the pocketbook. And although this engine was designed to run on low-grade fuels, according to a 1937 Hvid Diesel service manual, "… they will also run on any other standard grade of Diesel fuel thin enough to flow through the fuel pipes, whether it is distillate, fuel oil, crude oil, or any other similar oil."

How it Works

In a typical 4-stroke configuration, as all Hvid-type engines are, we can look at Figure 1 and assume the piston (B) is at top dead center, having just completed the exhaust stroke, and that the exhaust valve is closed. As the piston moves towards the bottom of the cylinder (A) on the intake stroke, the intake valve (C, Figure 2) opens and air is allowed to enter the cylinder throughout the stroke. While this is occurring, the fuel inlet valve (10) simultaneously opens to let oil enter the cup (3).

At this time, a little air, controlled by the adjusting screw (16), is drawn through a passage (6). The cup, as well as the air within, should now be heated to about 1,400 degrees Fahrenheit, as the air in the combustion chamber has been compressed to about 500 psi. This little bit of air within the cup, along with the heat of the cup itself, will produce vaporization of the more volatile elements of the fuel when the piston compresses said air.

Just after the piston reaches the bottom of the intake stroke, the inlet valve closes to allow for compression. The vaporized air is then held within the cup during both the intake and compression strokes.

Near the end of the compression stroke, the air within the annular chamber (4) is increasingly heated as the air is compressed. When that air is hot enough, it will ignite the vaporized air in the cup at TDC, creating combustion. The combustion is confined inside the cup and generates about 800 psi of pressure, which forces any remaining fuel out of the tiny holes (18 and 19) in the cup's surface and into the hot combustion chamber. After combustion, the remainder of the power stroke is completed in the usual manner as the burnt fuel expands and the exhaust stroke begins.

The Hvid Diesel service manual's explanation may be easier to follow: "There is now a mass of red hot air under high pressure in the combustion chamber. This hot air rushes into the fuel cup through small holes near its bottom and ignites the oil in the cup, causing a small explosion which forces the burning oil out of the cup, into the air in the combustion chamber, more or less completely vaporizing the liquid fuel in the process. You can therefore see that fuel ignition and injection are caused by compression and heat in the cylinder."

Speed governing is ad-justable through the needle valve (17), which regulates how much fuel is inducted into the cup. The March 10, 1918, issue of Motor Boat noted that this regulation took the place of the spark and throttle control on a regular gas-powered engine. It went on to say, "There is no throttle on the incoming air, as no matter how large or how small the amount of fuel used, the required compression must be maintained in order to ignite it."

The vehicles we drive today are much more fuel efficient than earlier vehicles, and they produce fewer pollutants. This didn't just magically happen one day - it took a lot of trial and error by thousands of people over the years to get where we are now - people like Rasmus Hvid. And although his engine wasn't a huge success, it was a springboard in gas engine fuel economy.

Special thanks to Glenn Karch for supplying us with necessary information with which to study and reference this patent.

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