Diesels are often considered to be slow and many car guys dislike them, mostly for the sound, but also for their performance…but why exactly?
Modern diesels are more refined and efficient than older ones, so let’s not take them, but a 20 year old diesel and petrol example:
Petrol E46 320i pre-facelift:
1991cc
150hp
190nm/3500
9,9s 0 to 60 time
219 km/h
Diesel E46 320d pre-facelift:
1951cc
136hp
280 Nm/1750
9,9s 0 to 60 time
207 km/h
Similar thing with modern VW engines, the Tiguan 190hp has pretty much the same 0 to 60 (half a second more or less) between the petrol and diesel and the top speed is also around the same, with a big consumption saving for the diesel.
So what is the reason for the perceived image of them being slow? Their turbo kicks in later? Them not being used in hypercars?
Diesels are low (engine) speed sluggers while petrol engines deliver at higher revs. You can see this in the figures you quote, max torque for the diesel is @ 1750rpm while the petrol equivalent is @ 3500rpm. (And it is torque that determines acceleration due to the ‘turning effort’).
Ignoring the sound (which I detest), and the weight (up to 2x a petrol engine) diesels just are not ‘sporty’ engines…
Now, if I was to really be practical about it, the diesel is more economical (it stores more energy than petrol per unit), can be more relaxed to drive but … I just don’t like compression ignition engines unless it’s a huge Caterpillar crawler, a diesel electric loco or a ship engine - then they have a sound all their own.
(And yes, the car has an Ansa exhaust system and the bike Akropovics
Audi had great success racing diesel power race cars at LeMans from 2006 to 2008, winning all 3 years. The engine was a V-12 with twin turbos. Diesel powered cars also ran at Indianapolis and other types of open wheel racing. Saw one at a museum, a Caterpillar powered car that race at Indy and other oval races in 1952 and 1953.
Because they are not by design. Now you can design around it, but that’s basically trying to make a diesel work how a gas engine does naturally.
2 factors really hinder it, one is since diesel’s run at higher compression everything has to be heavier to withstand that. This means that the engine has to move its own mass, which is considerably heavier, back and forth or round and round faster.
The second one is the way fuel is delivered. At wide open throttle, which would be a performance operation. A gas engine has it’s full air/fuel charge available and ready to go at a spark’s notice and that full push can be timed to push the piston so that all that power has the full power stroke to extract. OTOH diesels inject it’s fuel into the engine DURING the power stroke, this means at wide open throttle much of that fuel will enter the combustion chamber after the most ideal time and can only deliver partial power as the piston has already moved before much of the fuel entered. But that last part is a large part of what gives diesels it’s power to pull, while a gas engine shot it’s load, a diesel can keep pushing more fuel in for the power stroke.
Yeah, I drove some diesels as part of my job (taking photos of whatever car the reporter was working on that week) in the late 90s/early 00s, and the Eurodiesels were peppy as hell and not what you would think of as a “diesel” car. I assume their rep is because of things like the old VW Rabbit (at least that’s the only diesel car I can remember from the 80s) and because of their traditional role as loud, high torque, lower speed vehicles designed to pull large loads, and mostly because not many people, especially here in America, have been in a diesel car in the last twenty or so years, if at all.
You don’t remember GM’s Oldsmobile diesel from the early 80s? It was Detroit’s answer to the question, “what if we made a diesel engine from parts designed for a gasoline engine?” The result set the Big 3’s efforts to put diesels in passenger cars back by years.
Must have been too young. I was born 1975 – just remember the Rabbit. That one reminds me a bit of the 1979 W123 Mercedes 200D (I think I have those numbers and letters right) that was the first car I bought with my own money when I moved out to Budapest in 1998. $1000. Fucking boat of a car to drive with a heavy-ass clutch (which I learned to drive stick on). Sold it six months later when I realized it was completely unnecessary and not really practical where I lived.
In general, people think of diesels as heavy work vehicle engines over here. Here, it’s generally what they’re used for. For ages they were used in non-turbo/supercharged applications in passenger cars, and in that form they’re pretty awful from an excitement standpoint. You can pull a trailer well, but you’re not going to win any drag races.
Now, you can put a turbo on a diesel, and it starts to deliver the same kind of excitement that a gasoline engine can. But those were pretty rare until about 20 years ago. There are plenty of diesel truck performance enthusiasts out there (they can make quite a dragster). But that’s pretty far from general sports car culture.
Acceleration is due to a combination of engine torque output and transmission gear ratio; it is the combination of the two that determines the torque at the wheels, which is in turn what determines acceleration. Providing high torque at very low rpm is useful for starting from a dead stop without roasting a clutch, which is part of why diesels are used in big trucks (the other part is fuel economy), but if you want to move with alacrity around a twisty racetrack - which means means countless instances of acceleration from places other than the bottom of first gear - you need power. You can get 500 horsepower from a 6-liter gasoline engine, but if you want that kind of power from a diesel, you’ll need 15 liters of displacement, which means an engine that weighs almost as much as the rest of the car.
I gather a significant component of their success was due to better fuel economy, which means fewer refueling stops. That matters a lot in a 24-hour endurance race. Fuel economy made so much difference that after the R10’s debut in 2006, they changed the rules for gasoline engines to level the playing field:
Due to the sheer Audi dominance, the IMSA instantly made changes to the rules in the season. The Audi was not pegged back but competitors were helped to push their pace up to the Audi level. All LMP1 petrols were to be run at 860 kg and had their fuel tank increased to 95 liters.
The average customer shopping for a mass-produced sportscar doesn’t care about fuel economy nearly as much as they care about engine power output (and to a lesser extent, torque characteristics).
The best power, torque, and efficiency for a piston engine happen when combustion takes place shortly after the piston reaches top-dead-center and begins its power stroke. This is true regardless of whether we’re talking about gasoline, diesel, or something else. Because diesels use a lot of excess air, they tend to produce more oxides of nitrogen (NOx) than gasoline engines; with emissions regulations tightening up in the past couple of decades, diesel manufacturers have tended to solve the NOx problem in part by choosing an injection timing that’s later than optimal; this keeps peak temperatures (and NOx production) down, but compromises efficiency/power/torque. Late-model diesel vehicles don’t have the kind of fuel economy that similarly-sized vehicles did two decades ago, and this is one big reason why.
Smoke isn’t much of an issue for late-model diesels. While late injection addresses the aforementioned NOx problem, the downside is that it also produces more particulate matter (PM, i.e. soot/smoke). However, the EPA has tightened PM rules along with NOx rules. The solution is the diesel particulate filter (DPF), a catalyzed ceramic filter that captures virtually all of the exhaust PM. During high-load operation (when exhaust is hot), the catalyst helps oxidize the captured PM; this is helped in some cases by an occasional spray of raw fuel directly onto the filter to kick-start the oxidation process.
In spite of all that, yes, I agree that the exhaust from even late-model diesels has a distinct odor, and I’m not crazy about it.
I consider myself an “automotive lay person” in that I have no deep knowledge of either technology. When I hear “diesel”, I think of lumbering semis which, though impressive in their own right, aren’t remotely “sporty”.
Of course - but was just speaking in generalities and didn’t want to overcomplicate it by mentioning gearing…
Also, never did say diesels were not, or could not be fast, there’s a couple of examples above of ‘sporty’ diesels and even a Le Mans winner - it just that, to me, the characteristics of a diesel engine (low revving, slower throttle response due to the inertia of relatively heavy components like pistons and crankshaft, and the damned noise do not add up to a ‘sporty’ experience.
You don’t get that with any modern diesel car of the last at least twenty years, maybe more. The diesels I have driven I would not really have known are diesels (at least as a passenger) were I not told. Eurodiesels can be quite a nice ride.
One reason for this is that diesel fuel in Europe has a higher cetane number than diesel sold in the US. A higher cetane number correlates with a shorter ignition delay for the fuel, which in turn results in a more gradual cylinder pressure increase during the earliest part of each combustion event. This results in diesel engines in Europe operating with a less obnoxious sound/rumble than those in the US.
Ah ha. That’s interesting. Yeah, I don’t remember any of the modern diesels I had driven to be any louder than their petrol counterparts. But they were all driven in Europe, and I have no idea how the same vehicle would compare here with our diesel fuel. Still, I’d be surprised if they behaved like the diesel work vehicles most people think of when they think of “diesel” in terms of noise, stink, and smoke.
I question the premise that diesels are not considered sporty. I think it’s accurate about cars, but there’s a whole different demographic that has their own interpretation of sporty, centered on pickup trucks with diesel engines. They install ridiculously oversized exhaust pipes (often just at the very end of the exhaust system), they modify the engine control program to make it burn in a reducing combustion that creates a huge amount of thick black smoke and call it “rolling coal”, and talk a great deal about it all. I think in that context, it is sportiness.
The family that lived across the street from where I grew up had two Olds diesel station wagons. Their garage interior was coated in black soot. Cobwebs were highly visible.
It looks like you are using the former definition, but I think the OP (and the rest of us) had the latter definition in mind. If you’re looking for a vehicle that’s fun to drive on twisty roads (Deals Gap comes to mind) at a sporting pace, a diesel-powered vehicle is not the first thing that comes to most people’s minds.