Aspects Regarding the Combustion of Hydrogen in Spark Ignition Engine

Comparing to the hydrocarbons, hydrogen has very large flammability limits (in normal conditions 4 to 75% vol.), a high flame propagation velocity (5 to 8 times higher) and a low value of the ignition minimum energy (approximately 10 times less). All these properties strongly designate hydrogen as a favorable fuel to be used in engines.

So, there could be used lean and very lean air-fuel mixtures and the engine can be operated through the quality adjustment of the load (without throttle), with benefits regarding the engine efficiency.

Due to these properties, when using hydrogen in the engine there are signs of abnormal combustion, especially in the range of stoichiometric air-fuel mixtures:

Spontaneous ignition followed by flame occurring into admission, or pre-ignition followed by a rapid pressure increase while performing the compression;

In order to avoid the above mentioned abnormal combustion phenomena, authors have advanced the concepts of a hydrogen fueling installation that consists in the hydrogen admission inside the cylinder at the beginning of the compression stroke, after the inlet valve closing. The equipment allows the adjustment of the hydrogen in-cylinder admission moment.

The uncontrolled ignition is in this way avoided due to the cooling of the cylinder volume assured by the inlet air which after that will feed the combustion.

The used method avoids the per liter output decrease because it doesn't diminish the inlet air quantity (at relative air-fuel ratio λ=1 hydrogen displacement is 1/3 of the total usable volume). The paper presents results of the theoretical and experimental investigations which have been conducted on a SI mono-cylinder engine.