Diesel engines easily run 400.000km especially Mercedes cars but petrol will give up way sooner
In: Engineering
It’s a different principle. Diesel engines run at higher temperatures and pressures (making them more efficient). They don’t need spark plugs for example because they rely on auto ignition. This also removes the need for complex timing components.
So they have less parts.
In addition they also deliver more torque, which means you require less rpm for the same level of power (power = torque x rpm). This also means lower piston speed and less wear overall.
*Looks at all the Prius taxis*
*Shurg*
I guess most companies just don’t want to put the funds into R&D or something so the engines can hit the sort of mileage most cars will never see because other problems results in them getting scrapped. Outside of the US, a lot of people aren’t driving particularly far day to day.
Former diesel mechanic turned instructor turned field trainer. There are a lot of reasons that diesel engines tend to have better reliability.
1) diesel fuel acts as an upper cylinder lubricant. This allows the cylinder walls to last much much longer than a gasoline engine.
2) most diesel engines are built with much stronger components. There are two reasons for this. One, the higher cylinder pressures and two, reliability is more important.
3) use case. This is the big one. Diesel engines (especially large ones for semi trucks) spend much less time doing city driving, and considerably more time cruising at highway speeds. Acceleration, and starting the engine, are the two largest periods of wear on an engine. Driving back and forth to the grocery store for 3,000 miles produces much more wear than a 3,000 mile cross country trip. Additionally, the end user has much different priorities. Increasing the cost of a car by a large amount so it can run 750,000 miles before the engine needs an overhaul isn’t really something the average consumer would pay for, as most people don’t keep cars that long. A diesel engine in a semi is much much much more expensive, because down time isn’t just an annoyance. Any time that truck isn’t moving, the operator is losing money in a very measurable way.
There is more to it, like driver training, but really these are the biggest reasons. Apologies if anything was incoherent, I just got in from washing my wife’s car and mine.
One of the big factors is that diesel engines generally operate at a lower rpm. Think of it in terms of total rotations in a lifetime. Any engine rotating faster will reach the end of its life faster.
– Diesel engines have no spark plugs. They rely on really high compression ratios to combust the fuel by pressure alone. That’s less parts to break.
– Adding onto the last point, the internals are generally beefier so they can withstand these compression ratios.
– To achieve the higher compression, the crankshaft has a wider radius and I think longer rods, in order to increase the engine stroke. That greater diameter that the crankshaft journals have to travel for each revolution (compared to petrol engines) has the side effect of decreasing how much RPM they can handle/need to deliver the greater torque (This is also why diesels have less horsepower, which is just a measurement of how quickly that torque is applied over time). You may notice that diesels have redlines lower in the rev range because of this.
This is a lot of words to say that less RPM means less wear on the engine.
– Diesel is a lubricant, while gasoline is a solvent. Your engine oil is the most important thing for preventing wear. Diesel fuel in the combustion chamber just straight up reduces wear. In the case of gasoline, it does the exact opposite, basically washing away a fraction of the engine oil that’s busy trying to keep your engine from exploding.
– This isn’t inherent to either engine, but rather what they’re used for. As others have stated, diesels are more often the vehicles that cruise highways at a steady RPM, using their power to haul something. Gas cars are more often the ones driving to and from work in the city. Turning the engine on while it’s cold, and frequent stopping/starting is where 90% of your engine wear comes from, hyperbolically speaking. 10,000 miles of 5 minute commutes to work is gonna be way harder on the engine than 10,000 miles of 3-hour supply runs to and from a construction site.
I think that covers everything. Someone correct me if I’m wrong.
Source: Jobless college student that likes engineering
you need to walk through a few dealer workshops and see what engines are being replaced under warranty.
-edit- you probably live in the USA where the only people who use diesel are doing long haul.
So there’s a a false assumption here that it’s not possible, or even LIKELY for well made gas (petrol) cars to make it to 400k+ miles. Properly serviced reliable vehicles will do this every damn time unless there is some form of mechanical failure that makes the mantenence not worth the price.
Every gas car I’ve ever owned has made it well past the 250k (402k KM) mile mark. I have a jeep in the yard at 260K miles (418k km). The engine’s still in great running shape, it’s the transmission that would cost more than the vehicle’s worth to repair.
Diesel engines are designed to withstand higher pressures and temperatures. The fuel in diesel engines ignites through compression alone, which requires a stronger and more durable construction to handle the extra stress. This robust build helps diesel engines last longer. Diesel engines run at lower revolutions per minute (RPM) than petrol engines. Running at lower RPMs means less wear and tear on engine components over time, contributing to their longer lifespan. Diesel fuel has a higher energy density than petrol, meaning it provides more energy per unit. Diesel engines are also more efficient at converting fuel into mechanical energy, which translates into better fuel economy and less strain on the engine. Diesel fuel has better lubrication properties compared to petrol, which helps reduce wear and tear on engine components. This is important for maintaining engine health over long distances. Diesel engines are often used in heavy-duty applications like trucks and industrial machinery, so they are built to handle tougher conditions and heavier loads. This heavy-duty design carries over to consumer diesel vehicles, enhancing their durability. In contrast, petrol engines are built for higher performance and speed, often at the cost of some long-term durability. They operate at higher RPMs, which can lead to more wear and tear over time.
Primarily market pressure. Manufacturers want to build their products as cheaply as possible, this is only counterbalanced by consumers buying another brand because this one is a piece of shit due to how cheap it was made. Buyers of trucks with diesel engines are primarily businesses who will also calculate maintainence and repair costs as well as longevity in their purchasing decision. Buyers of cars with gas engines are mostly upper middle class people, who will turn around and trade this car in in a couple years for another brand new one, with very little thought given to how long it lasts overall. Also keep in mind that manufacturers don’t give a half a rat’s ass about people who buy their cars used, a car manufacturer makes no money on that transaction, as they’re not involved.
What this boils down to is they can cut more corners and make the gas engine less long lived because their buyers don’t care, they mostly have sold the car to somebody else by the time the warranty is up anyway.
The fundamental difference in the engines is that petrol/gas compresses a mix of fuel and air. This has far reaching implications and makes gas engines about 4x as delicate because they’re complex. Diesel engines are very simple and don’t need any predictions to run well.
Diesel engines inject the fuel at the last second once the air is already compressed. Diesel engines do not use spark plugs, so there is no potential issue with timing, supply, quality, etc of a 2nd thing. Gas engines must control spark, fuel, and air flow in a tight range. This is complex and the measurements and adjustments are all made based on readings from past events (for example Oxygen sensors read the average of the last several combustion cycles over a few seconds) and predictions are based on those. There is a lot of uncertainty once you account for the cumulative effects of all these measurements and predictions.
Diesel engines on the other hand control fuel injection rate. That’s about it. Air is unrestricted and spark is nonexistent. There is no real need for prediction of much of anything. Devices like EGR are used on both technologies and help deal with things like high combustion chamber temperatures based on exhaust temperatures, but that isn’t strictly required for diesels to run.
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