Plasma spark plug allows economical, clean gasoline engines
The discussion about nitrogen oxide and fine dust emissions, health hazards and driving bans for cars with diesel engines has given the petrol engine a new boost. As a result, the task of making this engine type more economical is once again taking center stage. Researchers have been working on the question of whether this goal can be achieved by using a rather lean fuel-air mixture for combustion in the cylinder. Lean engines are primarily interesting because of their increased efficiency and also have some other advantages. However, the problem arises when it comes to ignition: gas pressure and temperature are very high; in addition, a lean mixture is more difficult to ignite. A conventional electric spark plug cannot be used here – the wear is too great due to the increased stress. In the past, attempts to develop laser spark plugs also came to nothing.
This is where the spark plug, developed by Prof. Heuermann on the basis of plasma technology, comes into play. In physics, the term plasma refers to a gas that consists partly or completely of free charge carriers, i.e. ions or electrons. 99 percent of the visible matter in the universe consists of plasma. Natural plasmas on Earth can be found in lightning, for example, and flames are also plasma-like. In the spark plug, the ignition spark is replaced by this plasma, optically recognizable by a pink-purple flicker.
According to Hermann, the core of the development is the control electronics. These electronics ensure that the frequencies required for plasma generation are provided in the microwave range (2.45 GHz). “We can use a bandwidth of about 80 megahertz within the microwave spectrum,” says Prof. Heuermann, “this allows the frequency to be varied in order to ensure the highest possible energy absorption and thus efficient plasma generation. The control ICs measure the actual signals and compare them with a reference signal; the frequency is adjusted in a feedback loop.
The question remains when the plasma spark plug will go into series production. “With a series of tests, most recently a pressure chamber test, we proved that your spark plug works,” says the researcher. It is conceivable that the technology will be used in about two years. Large stationary natural gas engines are particularly suitable, for example in combined heat and power plants. Here, extreme lean operation is best implemented due to the uniform load profile. In the field of car engines, the challenge is that speed and power vary. This makes it necessary to adapt lean operation to different operating conditions. In the future, the technology could also pave the way for so-called “multi-fuel” solutions, i.e. the use of different fuels in one engine.
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