Short answer: diesel engines waste less fuel. Long answer: also short, because nobody came here for a lecture. Here are the four reasons, with drawings.
1. Diesels squeeze harder
Gasoline engines squeeze gently, about 8:1 to 12:1, or the fuel lights up too early. Diesels squeeze only air, up to 25:1, so they can go full gym bro. More squeeze means more of the heat turns into push.
2. Diesel fuel packs more punch
A liter of diesel holds about 13% more energy than a liter of gasoline. Same tank, better lunch.
3. No throttle, no straw
A gasoline engine controls power by choking its air supply. A diesel just injects less fuel and lets the air flow free. Less wheezing, less wasted energy.
4. They cruise, they don’t scream
Diesels pull hard at low revs, so they cruise relaxed instead of howling at 4,000 rpm. Calm engines drink less.
The fine print
- It costs more to buy.
- It needs a particulate filter, and often AdBlue.
- It makes more NOx and soot than gasoline, so the filters matter.
- It hates short trips, because the filter never gets hot enough to clean itself.
Score card
| Round | Diesel | Gasoline |
|---|---|---|
| Squeeze | 14:1 to 25:1 | 8:1 to 12:1 |
| Energy per liter | 38.6 MJ | 34.2 MJ |
| Throttle | None | Yes |
The takeaway
Squeeze hard, carry more energy, skip the straw. That is the whole trick.
