Microlighters

I am curios about the use of jet a1 in the thielert diesel aircraft engine, maybe some fo the engineers on the forum can answer my questions.

I am of the opinion that jet a1 has a higher octane than that of ordinary diesel feul, and therefore, when used in an engine designed to run on diesel, wil produce more torque, and for this reason, more heat.It would also produce more compression more rapidly, wich could not be healthy for the conrods and crankshaft.Because the explosion is more powerfull, there could also be a terrible pinging from the engine.

The sleeves in diesel engines are also lubricated by the diesel, as oposed to oil in petrol engines, how is this adressed when using jet a1?


In short, was the original renault engine modified by thielert for the use of jet a1, or can my faithfull bakkie engine be jammed in to an aircamper and run hapily ever after on jet a1?

Diesel aviation engines are very specifically designed units. Diesels are normally a lot heavier than gasoline engines because all the components are engineered stronger to cope with the higher compression ratio's (some up to 22:1 vs gasoline 9:1) and higher developed engine torque. Diesels can't "ping" like petrol engines because prior to injecting the diesel there is nothing in the cylinder to burn. A petrol engine has a mixture of petrol and air that was sucked in on the intake stroke - pinging happens when this mixture is ignited by hot engineparts/compression prior to the spark plug firing and this can cause serious damage. The octane number of fuel is indicative of it's resistance to pre-ignition. Avgas at 100 is a lot more resistant to pre-ignintion than 93 unleaded. In a diesel engine the fuel does not "explode" but burns as it is injected while the piston is forced down by the burnt gases.

The diesel does not lubricate the cylinder walls. This is done by the engine oil and the amount is controlled by the oil scraper rings. Lubricity of Diesel fuel is required for the injection pump (If you run your diesel car on JetA1 the pump will wear out very quickly). Aviation engines got around this problem by designing a pump that can run on low lubricity fuel like JetA1. The sulphur in diesel is also a lubricant for the injection nozzles (don't know how aero diesels get around this one).

The diesel engine is definately the way forward in engine design as it gets around some of the problems that make petrol engines so un-efficient (compression ratio limitations being one).

Diesel does have advantages and disadvantages:
+ No spark plugs
+ A lot safer in a prang (doesn't explode as easily as avgas)
+ Very good fuel economy (40% +!!) & it is cheaper
- High engine loads requires stronger (heavier) components
- Hig torque loads means your prop has a hard life (They use plastic props to combat this)


There is hope for microlighters that want o convert to JetA1 - Have a look at Hirth's UAV website. There is a spark ignition JetA1 engine that they might release by 2008 for experimental aircraft (although not a compression ignition engine at least you can say it uses the same fuel as a F18!!)

That is a lot of facts that i did not know, always helps to pick someone else's brain!