The Technical Questions Thread

[Kitdy]

I think you mean to ask why NA diesel engines make less peak power than similarly sized NA petrol engines right? The simple answer is that because diesel engines are designed to be stronger they cannot rev as high (ever noticed that diesel engines almost never rev past 5000RPM?). There are ofcourse other factors like: because they are designed with a higher compression ratio the valve system cannot be properly optimized for high RPM flow ect. ect.

So according to you, diesels engines can't rev high because of their strength, a high compression ratio interferes with valve timing...

well yes. but because diesel takes longer to burn it cannot allow high revs.

...but according to jediali, it is because diesel gas takes longer to burn. Is it a bit of both, or is one of you wrong?

If diesel takes longer to burn, would it help the situation if there was a spark plug?

I think you have misunderstood something if you have to ask this question. A diesel engine is not called a diesel engine simply because it burns diesel fuel but because it is a Heterogenous Compression Ignition engine that works according to the Diesel cycle (as opposed to the Otto cycle that petrol engines use).

The fundamental difference being that the Otto cycle includes spark plugs, yes?

Yes it is less efficient. Higher compression ratio = higher efficiency.

According to jediali, higher compression ratios aren't used in gasoline engines as the air/fuel mixture will prematurely ignite and cause knocking?

This is actually being done it is called a HCCI engine (Homogenous Charge Compression Ignition).

This new engine then somehow counters the fact that gasoline is volatile and likely to explode before full compression is completed then?

Yes ofcourse but why?

In an automotive setting, would not a two-stroke with (an) overhead cam(s) be superior to the standard two-stroke layout due to superior efficiency?

I am not sure why two-stroke diesel engines don't appear in cars I would imagine it has something to do with emissions?

On the shitty little article I read about diesel two-strokes on how things work, they said that the air need be compressed via a supercharger or turbocharger. Maybe this would not be the case if a diesel two-stroke was designed with a camshaft? Am I making any sense?

heterogeneous - occurs in petrols and throttles air supply and adds appropriate fuel quantity (ideally stoichiometric, 14.7:1) therefore cylinder size does not necesarily represent air/fuel mixture volume entering hence lesser volumetric efficiency.

homogeneus - always allows fuel provision of air to cylinders, this time accelerator adjusts fuel deliverd through injectors (usually direct into cylinders) therefore maximising volumetric efficiency and reducing unburnt fuel.

So a homogeneous setup is superior then?

clever stuff this...worth looking out for. vauxhall are running this as we speak. this has been allowable through advancements in ECU and engine tolerances. I also think it has a lot to with good combustion chamber where there are no hot spots (hottest point of combustion chamber which sets of fuel to early - usually the exhaust valve or something else sticking out).

This will then increase horsepower somewhat then yes?