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Car manufacturers are constantly trying to improve the efficiency of their cars to reduce fuel consumption and meet ever stricter emission standards, diesels are by design more efficient than comparative gasoline engines so how come we don't see many diesel powered toyota priuses on road instead of the typical gasoline ones?

I'm guessing the answer is the same for most of these questions which is usually cost. But what is the technical answer?

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  • Have you ever seen any diesel hybrid? Apr 28, 2023 at 23:47
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    There are a few diesel hybrids, but the death knell is tolling for diesel cars anyway. Although sales of conventional diesels in UK outstripped petrol in 2010, the emissions requirement has become tighter, and sales have fallen drastically. The Euro5 NOx emissions were slashed to less than half for Euro6, and for these diesel vehicle in UK any visible smoke from the exhaust means a MOT test failure. Diesels are dirty engines: especially particulates, and they now need a removal system which adds to the manufacturing cost and is expensive to repair when it fails. Apr 29, 2023 at 17:26
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    At the same time the efficiency of petrol engines has increased, with mpg figures unheard of in the past. Traditionally, diesels were the engine of choice for working vehicles: high mileage and continuous running, but more expensive fuel and manufacturing. Today's stop/start and hybrid technology means intermittent running: diesels take more energy to start and these are not the ideal conditions for them. For these reasons some professional users are moving away from diesel, and some low-emission city zones penalise any diesel vehicle that is not the latest standard. Apr 29, 2023 at 17:26
  • Additionally, diesels are not as efficient as many folks believe. See the V.A.G. scandal on faking results in testing as one example.
    – Rory Alsop
    May 1, 2023 at 8:08
  • @DavidRemembersMonica Peugeot made a diesel hybrid 3008 until 2016, with pretty decent reviews (I kind of wanted one around 2013 but it would have meant buying brand new)
    – Chris H
    May 5, 2023 at 13:45

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If Europe were still subsidizing diesels it might've happened, but that ship has sailed. People didn't use diesels in passenger cars in Europe because they were great, it was because the government had low taxes on diesel fuel.

Gas engines produce more power than diesel engines. A hybrid engine will often run at max rpm, producing the maximum power. Diesel engines don't rev as high and thus produce less power. A heavy less powerful engine is not desirable in a consumer vehicle.

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    Power is only proportional to RPM for a single engine. Diesels tend to provide more torque and can produce more power, but need slightly different gearing
    – Chris H
    May 5, 2023 at 13:47
  • @ChrisH, no. Power is always proportional to RPM because RPM is in the equation. Torque is dependent on gearing, power is not. This is why semis have 20 gears. A similarly sized gas engine will virtually always make more power than a diesel.
    – Tiger Guy
    May 5, 2023 at 20:46

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