Diesel cars can be banned from German cities, court rules • Hacker News Board

Re: Diesel cars can be banned from German cities, court rules

#341

Post by mywittyname » Thu, Mar 01, 2018, 3:46 PM UTC

kazinator wrote: post #317

mywittyname wrote: post #316

Earlier quoted context omitted.

> the diesel will win just about any street race. This is really wrong. It's a weird myth that gets perpetuated in America where people don't really drive diesels. Let's compare a 2.0L diesel Golf TDI to a 2.0L petrol Golf GTI. Same car, same displacement, both turbo engines. The Golf TDI does 0-60 in 9.0s and a quarter mile of 17.0s@84 mph. The Golf GTI does 0-60 in 5.7s and a quarter mile of 14.2s@100 mph. There's…

If it were true, Formula-1 would use nothing but diesel engines.

This comment makes no sense. I'm saying diesel engines are bad for performance. It's not physically possible to make a diesel 1.6L engine that produces F1 levels of power, they just can't spin fast enough.

Re: Diesel cars can be banned from German cities, court rules

#342

Post by mywittyname » Thu, Mar 01, 2018, 4:04 PM UTC

bdamm wrote: post #338

mywittyname wrote: post #316

Earlier quoted context omitted.

> the diesel will win just about any street race. This is really wrong. It's a weird myth that gets perpetuated in America where people don't really drive diesels. Let's compare a 2.0L diesel Golf TDI to a 2.0L petrol Golf GTI. Same car, same displacement, both turbo engines. The Golf TDI does 0-60 in 9.0s and a quarter mile of 17.0s@84 mph. The Golf GTI does 0-60 in 5.7s and a quarter mile of 14.2s@100 mph. There's…

I think the 0-40 profile would be much more favorable to the TDI, and much more useful to the typical driver. But we'll never really know as that's not the standard measurement.

The diesel golf is still a lot slower to 40 than the GTI. The TDI diesel has a lot of turbo lag, a narrow powerband, and poor gearing. What people who've never owned diesel cars fail to realize is, that peak torque number is hugely misleading. It sounds impressive, but it starts from like 2200RPMs and falls off a cliff past 3500. While a (modern) turbocharged petrol engine has full torque by ~1800rpms and that lasts until like 5000rpms.

I've owned a (Jetta) TDI before, I even tried to make it fast. Even with a tune and full exhaust it was slower than a stock turbo petrol.

It's always Americans that talk about how awesome diesels are. I never see posts from Europeans (who are the ones that actually have to drive them) talking up diesels. They are always complaining about how terrible they are.

Diesels are great for trucks, but not cars.

Re: Diesel cars can be banned from German cities, court rules

#343

Post by mywittyname » Thu, Mar 01, 2018, 4:19 PM UTC

MasterPI wrote: post #330

mywittyname wrote: post #281

Earlier quoted context omitted.

Diesels have literally the worst powerband for automobiles, especially mated to automatic transmissions. Diesels have power down low in the RPMs, but that's never where you are when you need power. When you need to accelerate, you floor the throttle and the transmission downshifts into the upper RPMs. They are good for accelerating 0-40, but they are significantly slower at 40+ -- which is where most people accelerat…

:) Please specify when you talk about small diesels. Non of that 0-40 acceleration is true for the 535 I mentioned in my previous comment.

No replacement for displacement does hold true for diesels. I've seen some crazy fast, crazy large diesel pickups at the drag strip. 3.0L is about the displacement diesels can start making power, anything below that the limitations of physics are holding it back.

Re: Diesel cars can be banned from German cities, court rules

#344

Post by kazinator » Thu, Mar 01, 2018, 4:48 PM UTC

mywittyname wrote: post #341

kazinator wrote: post #317

Earlier quoted context omitted.

If it were true, Formula-1 would use nothing but diesel engines.

This comment makes no sense. I'm saying diesel engines are bad for performance. It's not physically possible to make a diesel 1.6L engine that produces F1 levels of power, they just can't spin fast enough.

The comment make sense, since I'm saying "[i]f it were true [that diesels easily beat gasoline burners in a street race], Formula-1 would use nothing but diesel engines [which they don't at all]."

Re: Diesel cars can be banned from German cities, court rules

#345

Post by scrumper » Thu, Mar 01, 2018, 5:29 PM UTC

blau3 wrote: post #313

scrumper wrote: post #113

Earlier quoted context omitted.

Back in the late '90s when I got my first diesel (a Citroen AX, with what was at the time the smallest production diesel power plant available) you'd have to wait many seconds for the glow plugs to warm the car before trying to start it. Diesel also freezes in the extreme cold, though that's not really a major issue in the UK. You could also run it on used cooking oil. In the 20 years since then diesels have undergon…

> If you put old vegetable oil in them they would break instantly and expensively. Haha, an acquaintance of a local Linux user group I used to visit drives an old BMW which he has modified to run on vegetable oil. To be precise, oil which has been used for preparing french fries. You can easily recognize the smell. He was a car mechanic, I guess he knows quite well what he does.

Yep. A basic diesel engine is a pretty amazing thing that, like a jet engine, can burn pretty much anything and is simple to maintain. Once you start adding all the modern gubbins in it to make it efficient and powerful, you lose that generality.

The main issue with using alternative fuels in modern diesels is the injectors: unit injectors and common rail systems are high pressure, precision components that are very sensitive to fuel quality. Used frying oil is not clean.

So your mate's BMW either had some modifications to let it use vegetable oil reliably, or it's really old!