Cetane and diesel performance
It’s all about combustion, whether you are running a gas or diesel engine. With a gas engine, octane is key. The higher the octane content of gas, the more pressure or heat that fuel can resist before combusting. In diesel fuel, it’s all about cetane.
A diesel compresses intake air so much that it reaches a temperature of nearly 400°F., which is the ignition point of the fuel. Once the air is compressed, the fuel is injected and ignites. Unlike a gas engine that premixes fuel and air, the fuel and intake air mixture in diesels is not uniformly mixed.
To combat this, the spray pattern created by a diesel injector looks like the legs of a spider or a seven-hole liquid fertilizer tip on a sprayer, but in atomized form.
Cetane Is Diesel’s Desire to Ignite
Diesel fuel’s eagerness to ignite is paramount not only in getting the engine to run but also in improving the quality of fuel combustion and timing of combustion in the crankshaft’s rotation. The willingness of diesel fuel to combust is called cetane. The higher the cetane rating of the fuel, the sooner that fuel will ignite and at a lower engine temperature.
Cetane can be likened to several areas of crop production, collectively. It can be compared to seed-to-soil contact, in-furrow fertility, soil moisture, seed depth, soil tilth, and temperature. When all these variables are at optimum levels, the plant emerges quickly without expending excessive energy.
Establishing the Reaction Zone
In like fashion, when diesel fuel has a high cetane rating, all aspects of the chemical-to-mechanical energy exchange work harmoniously and efficiently. In both gas and diesel engines, once combustion begins, a region called a reaction zone is established. This is where the heat travels from the burned to the unburned regions of the fuel.
That is why a diesel engine, when it’s cold and is first started, runs very poorly; the reaction zone in the piston hasn’t yet formed.
A modern engine usually keeps the glow plugs and/or the intake air heater evoked so that the reaction zone occurs sooner. Once there is uniform heat in the cylinder bore, the reaction zone, in its original form, is no longer present. At this point, the entire bore of the engine is at the ignition point of the fuel.
Just as it would be impossible to have high crop yields without a properly balanced soil (in terms of base saturation on a soil test), efficient combustion and, in turn, the optimal performance of the engine are out of reach when burning fuels with a low level of cetane.
The goal is for the fuel to ignite as soon as possible (with a minimal delay period) so that its potential energy is used to work against the piston and transfer into the crankshaft.
Creates More Power
If the fuel ignites easily and completely, then the engine makes more power, consumes less fuel for the work that it performs, runs cleaner, and runs quieter. If the cetane of the fuel is insufficient, it will result in a noisier and coarser combustion event.
Also, Tier 4 diesel engines fed low-cetane fuel will create more soot particulates. The more soot an engine creates, the more regeneration cycles are required to clean out the diesel particulate filter (DPF) using additional fuel.
Cetane holds many of the keys for an engine to cold-start easily, run smoothly, keep its oil cleaner, and reduce soot buildup in a Tier 4 engine’s emission system. The big payoff to cetane in fuel for farmers, however, is that it helps generate more power while boosting fuel efficiency.