Plasma-Assisted Combustion

Liquid, solid and gas are the three well known states of matter; by subjecting gas to a large amount of electrical energy the fourth state, plasma, is formed.

About Plasma

Gas has a positive core with negative electrons orbiting around the core. A plasma is a gas that is heated to the point that the individual gas atoms break apart to make a collection of positively and negatively charged particles.

Plasma-assisted combustion is a relatively new area of study. According to the American Physical Society, “Scientists know that by introducing plasma to the reaction - near or at the location where the flame ignites - new chemical species are produced that catalyze combustion.” Recent studies have shown that highly reactive plasma can be formed by subjecting the gas in an internal combustion engine to large amounts of electrical energy within nanosecond timeframes. Plasma is highly reactive, igniting immediately and combusting rapidly. Large amounts of the remaining gaseous fuel can also be ignited instantly by the large ball of burning plasma-affected fuel. Understanding how to create plasma in an engine and how exactly does it benefit the ignition and combustion process are major topics in the automotive and natural gas industries.

For instance, this diagram shows gas atoms with a positive core and orbiting negative electrons. To form plasma, these gas atoms are subjected to a large amount of energy and broken apart to form a collection of positively and negatively charged highly reactive particles. Plasma consists of positively charged ions with most or all of their detached electrons moving freely about in a very active manner; these electrons react with other atoms.

Pulstar stores energy accumulated over a relatively long period of time in its internal capacitor and releases it entirely in less than three nanoseconds. This massive dump of energy happens so quickly that the pulse it forms is equal to 5 megawatts. This 5 MW pulse interacts with the gaseous air-fuel mixture, breaking its molecules apart. This is known as ionization, the process by which an atom or molecule acquires a negative or positive charge by gaining or losing electrons to form ions. By ionizing the gaseous air-fuel mixture, Pulstar breaks down natural elements like H2 and O2 into their atomic state of H and O where they are most volatile. Thus, the portion of the air-fuel mixture affected by the pulse has been turned into plasma.

Plasma created by the high-intensity pulse of energy results in three major benefits in fuel combustion: instant ignition and a quicker and more complete burn.

Instant Ignition

Temperature Increase. The high-intensity pulse creates a flash of heat that helps the fuel charge reach the required light-off temperature to ignite the air-fuel mixture. The flash point for gasoline is about 600oF and 1,100oF for natural gas. The heat provided by the plasma, gives the air-fuel mixture a head start to achieving the temperature required to ignite.

Volatile Air-fuel Mixture. The high-intensity pulse ionizes the gaseous air-fuel mixture, breaking down air-fuel components like H2 and O2 into their atomic state of H and O where they are most volatile. These highly excited elements along with radicals react to the ensuing spark by igniting instantly.

Quicker Burn

Fuel Fragments. The high-intensity pulse breaks apart the long hydrocarbon chains found in the nearby air-fuel mixture into shorter chains that react quickly. This area of the air-fuel mixture burns faster.

Complete Burn

Fuel Fragments. The portion of the fuel that contains shortened hydrocarbon chains burns faster, and creates a larger surface area to ignite the rest of the gaseous air-fuel mixture. This allows the air-fuel mixture to burn more completely during the power stroke.

Ionic Wind. The high-intensity pulse knocks off electrons from the air-fuel mixture molecules. These ions are thrown out of orbit and knock off additional ions from neighboring molecules, creating a cascading effect. This process helps expand the formation of plasma beyond the high-intensity pulse’s immediate vicinity. As previously mentioned, this plasma field burns at an accelerated rate.

SUN Wentng and JU Yiguang, (Princeton) J. Plasma Fusion Research Vol 89, No 4 (2013)

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