BYD's Engine Flexes Between Ethanol, Gasoline, and Electricity | Hacker News Reader

BYD's Engine Flexes Between Ethanol, Gasoline, and Electricity

spectrum.ieee.org

24 pointsthunderbong11 comments

Any car in Brazil already has to cope with a high ethanol mix (it’s now 30%, with plans for 35%), so not sure how they are making something “more accessible” when everything else in the market already has it.

Do they have some innovative measuring system? A better way to switch between ICE and electric based on emissions/cost/range?

You just need an Ethanol sensor + a little bit of software support in the ECU and your hybrid car can also run on ethanol, gas or electricity. However for some reason OEM manufacturers are just not putting the ethanol sensor into cars.

Does it require a $18.5 million investment (from article) from each manufacturer?

It does not. Flex fuel cars are widely used South America, especially Brazil where Ethanol is more available than gas. In North America or Europe it depends. Sometimes it is available directly from OEM, sometimes you need aftermarket modification to add Ethanol sensor to run engine with correct lambda.

Here you have list of Flex Fuel cars - cars which has Ethanol sensor and are able to run on gas or Ethanol.

https://en.wikipedia.org/wiki/List_of_flexible-fuel_vehicles...

I fought for a long time that ethanol and methonal up to some amount 30% or maybe 50% should have been made 'standard' fuel. For a long time a lot of natural gas was wasted that could have been turned into gas instead of blown into the atmosphere.

Granted electric cars made this less needed but before batteries as a technology broke threw, this was a great way to reduce emissions.

One of the issues is that fuel standard process were to slow, focused on only ethanol (in the US) and that car manufactures fought it.

But having a truly flexible fuel supply can do a lot for fuel prices and get them down. Specially after the natural gas boom in the US.

Is there a efficiency chart somewhere with multiple mixture ratios?

The following link has some charts for just the ethanol. They look about as expected. Some things get better the more ethanol you use, some get diminishing returns, some have an inflection point and get worse, some are just worse as you increase ethanol percentage.

https://www.researchgate.net/profile/Aimen-Zeiny/publication...

Fundamentally, ethanol will always be less efficient per gallon than gasoline. It has significantly less specific energy compared to gasoline. This is a fact known by anyone that has tried e85 either for racing or for flex fuel compatible normal vehicles.

But look at figure 8. At 40%, volumetric efficiency is at its peak. It's very important to note that these results are neither monotonic nor linear, so while the public only has access to E85 and E10/E15 (at least where I've been), those are almost ends of extremes and a middle ground can synergize. Yes some metrics always get worse the more ethanol you use, but hopefully you looked at the paper and saw that isn't nearly the full story.

I'm not sure what that proves? Volumetric efficiency is just about air efficiency. Higher VE is better, yes, but you need to compensate for higher VE by adding more fuel to utilize the air, otherwise you run lean, which is bad. Turbocharging a car, for instance, directly increases VE.

None of this directly equates to fuel efficiency although it can be related, which is what the GP was asking about presumably. You still need to content with the fact that ethanol has ~30% less specific energy per gallon.

Figures 8 and 9 show that both volumetric and thermal efficiency can be improved with nonzero ethanol in the right circumstances. Increasing efficiency metrics, while combining figure 7's showing that you get more power with ethanol, means that you're getting more power and doing so with greater efficiency.

You mention fuel efficiency. Figure 6 shows that in some cases, looks like the threshold is between 60 and 80% load, the story flips such that adding ethanol to the mixture reduces sfc. In other words, less fuel is needed for the same amount of power. Meaning, if it takes X hp or kw to sustain whatever test speed you're measuring efficiency at, the amount of fuel you use is lowered. I think this is very important to understand. Figure 6 shows that if your engine is sufficiently loaded, nonzero ethanol can improve the amount of energy you get out of the same mass of fuel relative to pure gasoline, which I believe would be directly proportional to better fuel efficiency.

Now very notably, if less heavily loaded, it seems better to use 0 ethanol. The ability to choose lets it get the best of both worlds.

Reply on news.ycombinator.com