Originally Posted by gmcjetpilot
Diesel is up to 20% to 30% more efficient and the fuel has 10% to 15% more energy density, and makes more low end torque than a petrol engine.
I drive a VW TDI Sportwagen and can get over 50 mpg highway, and it is a hoot to drive with low end torque starting from idle is 100% torque at 1750 RPM and stays flat as a board (in part due to torque limiter in computer, these cars can be uncorked).... Low speed around the corner acceleration is fun. Why not diesel in airplanes. Of course they have some. The issue is weight. Diesel engines are beefy to handle the pressures. Also certification cost.
The answer is Lycoming is supiror to any alternative engine... proven over and over.
The HP, FF, BSFC, charts are in the Lycoming manuals. This is for a Continental, BSFC looks like 0.38 is lowest.
If we are talking auto engines here, the latest SI engine designs from Toyota match the BSFC figures of auto light diesels. Toyotas Dynamic Force engines, introduced in 2018, have a thermal efficiency of 40-41%. https://www.sae.org/news/2018/04/toy...mal-efficiency
This is because the compression ratios are in the 13-14 to 1 range and the Otto Cycle is actually more efficient than the Diesel Cycle.
Diesels also don't produce more torque or more power than an equivalent SI engine of the same displacement at the same boost pressure. If you have an apples to apples example to support your statement, please cite it here.
Most OEM SI auto engines require a very rich mixture (around 11.0 AFR) at high power levels to keep piston crown temperatures down to survivable levels.
Despite the generally old tech in Lyconentals, they are surprisingly efficient at cruise. Running LOP in cruise, they can match the BSFC figures of 2 stroke aero diesels (think WAM) and come within a hair of 4 stroke aero diesels such as the Austro and Thielert. With the addition of high CR pistons, EFI, EI and tuned length intake and exhaust systems, they can match the diesels on cruise BSFC.
Dave Anders has done some great work in this area recently and you'll see some more info on his latest experiments shortly.