-HP is a function of RPM, defined by laws of physics.
True. HP=TQ*RPM/5252 to be precise.
Now that's incorrect. Torque = force/work. Torque does not take into account the duration of the effort. However, power = work over time, which is the only thing that really matters here.
Let's take two guys, Daniel and Peter. Daniel is big and strong, but can only move slowly, Peter on the other hand is weaker but can move faster. They both have to push pallets accross the room. Daniel pushes 20kg pallets and takes 10 seconds to cover the distance. Peter pushes 10kg pallets and takes 4 seconds to cover the distance. In 20 seconds, Peter will have moved 50kg worth of pallets, while Daniel will have only moved 40kg. Peter has more power here. However, Peter doesn't have enough force to break free the 20kg pallets from standstill, Daniel's torque is necessary there.
Understand better the difference ? If you need to move important weights and how fast you do it is not crucial, then you want Daniel's torque, who uses a long stroke. But if you need speed to do it fast, you'll need Peter's power, who uses a short stroke.
Details :
http://www.epi-eng.com/piston_engine_technology/power_and_torque.htm
Outright, peak HP in a diesel cannot be compared to that of a petrol engine.
False, because of what I explained just above. I might give you a point on the word "peak", as it would be better to look at a range of RPMs in which power is at least at a certain percentage of peak power. But you can't compare torque figures taken at different RPMs, because the number of cycles is different.
Moreover, if torque was the only thing that matters, why then make engines rev after torque peak ?
-Petrol only gain a slight bhp advantage but at a great torque loss.
Twice the HP for same displacement is not what I call a slight advantage.
-less reliable.... please, Diesel engines produce less heat energy and are more thermally efficient, do less rpm and as such wear at a lower rate
-Petrol runs at half the thermal efficiency
-Diesels are infact more reliable, they run stronger blocks and produce far less heat. [...] Modern cars do suffer thanks to emissions control equipment such as EGR's and DPF's which like to clog up but the engines themselves would run forever.
Petrol engines also improved with time, difference is less than it used to be in that regard. And by the way, it's not what I was talking about, because first I'm looking at efficiency regarding displacement, then because blocks in themselves don't break, unless something else goes wrong (which is more likely to happen on a diesel). Also, try to run a diesel engine at petrol RPMs, and we'll see how it deals with it.
So, back at reliability : what do we see in garages ? TDi, TDi, TDi, TDi... Core block doesn't break but that's not the point. Yeah, it may be a good part due to peripherals, but those are required, and doesn't break on petrol engines. Looking only at the core block makes no sense, and I can say petrol blocks could run forever as well (million miles petrol engines do exist, and I have driven several petrol cars with original engines over 300.000 km which were running more than fine : I especially think of a friend's Celica he bought new, which still even has original clutch despite the daily routaine being a mountain pass to go to work). And still, porous heads, rods and bearings seem to happen quite often.
And talking about TDi specifically, knowing several people who work or worked in VAG dealers, a brand new TDI acting up before the customer even has the keys handed is not a rare occurrence.
Modern day diesels are also very, very sensitive to impurities in fuel and injection problems. And injection problems are actually quite a big thing with the expensive stuff they must fit in.
Then, not being able to start under freezing cold temperatures does not go well with reliability. It was pretty funny around there to see the mess when temperatures went under 10° Celsius (I live in the Alps, so don't come tell me about specific low temperatures diesel in pump stations).
Taxi's, trucks, trains and every piece of industrial equipment in the world don't run diesels because they enjoy the soundtrack.
I'll assume you either messed up in writing, or there are regulations that kills the diesel where you live since in EU, pretty much every taxi, trucks and trains runs diesel. As for industrial machineries, Vallée de l'Arve in France is one of the country's most polluted area by particles because of industies (diesel machines, yes). Basically, freight and industries all use diesel because they move huge amounts of weights / need brute force, without the need for speed.
I have a 2 litre Turbo Diesel Subaru (boxer configuration) it produces 420Nm of torque at 1600rpm, and holds that torque until 3400rpm, it only drops to just under 400Nm at the redline.
Which makes 95 HP at 1600 RPM, and 150 HP at 3600 RPM. But where's the revlimit then ?
Also to note the Subaru EE20 D.I Turbo Diesel weighs no more than the EJ20/ EJ25 engines
Due to a fully aluminium engine construction, with steel cylinder liners.
It also uses no (heavy) balance shafts due to the boxer layout being harmonically balanced.
Yeah, now find me a 400+ HP diesel boxer without extensive modifications that will hold up on more than a drag strip. I can vouch for closed deck EJ20/25s dealing with those powers with no problem, know a lot of them around here.
-Modern diesels use ali blocks and heads the same as a petrol, costs are increased due to expensive injectors and pumps but the engines aren't much more at all.
Still produce less power at comparable displacement and aspiration. So less effective. And besides, that's higher end engines, most of which still needs to be reinforced.
-Low(er) Rpm's yes but twice as much work done per RPM
Yeah, and what ? Still useless, what matters is the amount of work per time units, as shown before.
-low RPM's are fine for performance....
No. That's a definite no. Explanations are just after.
and as the RPM range has increased towards 5000 so that is less of an issue. Besides it's the gearboxes job to worry about the engines RPM so as long as the gear ratios are good everything is fine.
Problem is not keeping the engine in power range, it's exploiting the gearing to better potential, as your actual speed is dependent of your gearing and RPMs. Let me explain with an example :
Cars A and B are identical in every regards, weight, gearbox, etc. except engine. Engine A delivers 200 HP between 3000 and 5000 RPM, while engine B delivers 200 HP between 5000 and 7000 RPM. Gearbox is stagged in a linear way, you lose 2000 RPMs when shifting.
Car A goes up to 50 km/h in 1st gear, while car B can reach 70 km/h before shifting. That means from 50 to 70, B accelerates better than A because it is still in 1st gear while A is already in 2nd.
2nd gear allows A to reach 100, while B will reach 140 keeping the same acceleration potential (aero drag neglected). Which means on a 40 km/h range, A has less acceleration again. The faster you go and the higher the gears, the difference increases. The only point where engine A might perform better is at take off on 1st gear, before 50 km/h. In race conditions, how much does that happens ?
See where this is going ? If not, here's a practical example from my own testings :
Time Trial Mountain Board
TL;DR : higher RPMs engine makes the car faster by 2.7 seconds on a single 4km lap.
LMP cars Use shell V-power diesel, its even delivered with a road hand pump flow rate and the engines are CI, there are no spark plugs, if there were they would be SI engines.
There ARE dedicated ignition spark plugs on LMP cars. I saw a R10 TDI engine block and a 908 HDI engine block in person. And I know the ACO prohibits the use of any kind of fuel not available at your regular pump station, that's not only for diesel.
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In the end, diesel has its sues, but the point I try to make from the beginning is that it is simply not designed or suited for a sports car / racing car application.
