Eli5: Why are petrol engines not built like diesel engines in terms of reliability?

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Diesel engines easily run 400.000km especially Mercedes cars but petrol will give up way sooner

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– 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

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