Why do combustion engines always say terrible knock-knock jokes?

July 10th, 2021

Automobiles have significantly improved the lives of humans – nothing is too far these days with a car. In our vehicle, we set off to drive for work, make a short spree to the local grocery store, cruise on a long road trip, get our packages delivered, and what-have-you.

We almost never notice the complex mechanisms of a car that reliably get us from point to point (until it breaks down…). Every time we start our car to carry out our business on the road and until we turn it off, there are, on average, a few thousand explosions per minute inside the engines of our car that set us in motion. That is almost 20 times every second for each cylinder!

Hidden Consequences of the “Bang” Part of Combustion

Spark plug ignites fuel-air mixtures by inducing a dielectric breakdown in the spark gap. In order to initiate the breakdown, sufficient voltage difference across the electrodes is supplied until the breakdown happens. This phenomenon leads to formation of a spark – a form of plasma and is akin to formation of lightning, but on a much smaller scale.

At such intense continuous operating conditions, every stroke of the engine causes the electrodes on the spark plug to undergo various phenomena such as melting, vaporization, sputtering, and oxidation. These processes cause electrodes to erode which leads to degraded performance of the engine. More often than not, when you are trying to start the engine – and it fails or if your car is sluggish, it is likely due to eroded electrodes which are causing this nuisance. Electrode erosion affects formation of spark between the electrodes.

The Issue…

Spark plug erosion is a complex multi-physics transient phenomena which involves coupling of surface physics (electrode depletion), thermal plasma physics (spark formation), circuit dynamics (ignition coils), turbulent chemical interactions (combustion) and heat transfer.

The spark between the electrodes lasts only for a few milliseconds, depending on the ignition system. On the other hand, the erosion of the electrodes could take up to years. Modelling misfires and erosion are arduous as the model needs to accurately capture multi-physics phenomena that occur in completely different time scales.

This poses a problem: how do you simulate physics of spark plugs which occur at different time scales, with highest possible fidelity, simultaneously, within a matter of hours?

The Solution

Here is where multiphysics capabilities of VizSpark opens new dimensions of understanding erosion – our thermal equilibrium plasma solver developed at Esgee Technologies, has been successfully used by major automotive companies to understand the spark formation and erosion behavior of the electrodes.

VizSpark provides multiphysics tools for mixing and matching electromagnetics, plasma, fluid dynamics, chemistry, circuit dynamics and many more, in a single easy-to-use framework.

Here’s How…

For example, our CircuitLib module in VizSpark allows for flexibility in a variety of configurations which power the electrode. The circuit parameters are coupled with the fluid dynamics module. This means you could generate a spark in a realistic manner as it would happen in an engine.

The figure on the left, captures variations in the spark properties which are reflected in the results generated by the coupling of physics. Industrial researchers rely on the highly resolved current and voltage readings to understand the misfires that lead to erosion. Using VizSpark simulation, they have developed a predictive ability to design high-efficiency spark plugs by optimizing electrode geometry.

Next comes the massively scalable multi-processor, multi-node capability of VizSpark which is implemented at all stages of the simulation: mesh partitioning and simulation. The video on the right shows our high fidelity 3D representation of the geometry involved in this study. Here the top electrode is grounded, while the bottom electrode is connected to a current source to power the spark plug. Here, the geometry is an accurate representation of a J-type spark plug. Using partitioned mesh, Vizspark takes advantage of parallel processing and speeds up the simulation by many folds.

Stay Tuned for More Details

In the meantime, feel free to check out the whitepaper and other ground breaking simulations. Follow us on LinkedIn!

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Tags: VizSpark Spark Plug Erosion

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