Quote:
Originally Posted by P-hack
But that kind of muddies the water. If you are building a train or a ship, then fine, but for personal transportation folks are comfortably getting to and from work on 1/4 liter or less, with emissions control even.
A 1.6l tdi can make 198 g/kwh, to get a %20 improvement in bsfc you have to go to something that has this for a crankshaft, so lets not ignore bsfc vs weight (or minim power required).
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Engine design is based on a myriad of choices and variables. Based on your specific need, designing an engine that runs as slow as possible results in more efficiency than one that is running faster. A few off the top of the head reasons is friction and engine drag. Also, combustion event is longer along with increased volumetric efficiency. If the cylinder is large enough, heat loss can be minimized and the results are better BSFC. Does the engine HAVE to be a colossal structure - of course not! Diesel engines are often also built for length of service as well as power production. Diesel aero engines are on the opposite end of the power/weight spectrum. Your mentioned VW engine is somewhere in the middle. Their service life also vary accordingly. But, design for a specific power output and the larger slower revolving engine will be more efficient. However, the need for flexibility to provide range in a road going application results in compromise.
Back to Firewalker's engine, since it is one already in his vehicle - it's large size can be an advantage assuming the other variables fall into place. It is almost an ideal test engine for what he is trying to do with combusting heavy oils.