Mixing diesel and hydrogen provides big cuts in emissions(arstechnica.com)
arstechnica.com
Mixing diesel and hydrogen provides big cuts in emissions
https://arstechnica.com/science/2022/12/mixing-diesel-and-hydrogen-provides-big-cuts-in-emissions/
2 comments
This is very interesting.
It's not clear though if this is a pure Diesel engine or a hybrid between an Otto engine and a Diesel engine. I tend to believe it's a pure Diesel, but that would be a pitty.
In an Otto engine, in the first cycle you absorb in the cylinder a mix of air and fuel droplets, which you then compress in the second cycle, and detonate using a spark in the third cycle. In the last cycle you release the burnt gases.
In a Diesel engine, you absorb just air in the first cycle, which you then compress in the second. You can compress to much higher pressure (and temperature) than in the Otto engine, because the compressed air can't auto-detonate. You then inject fuel, which ignites immediately (no need for a spark plug). You have a slight problem: apart from the first few particles of fuel, the next ones will not find too much oxygen around, since it was already used to burn the first fuel. You solve that by insuring the geometry of the cylinder and piston is such that there is good turbulence going on. Lots of computer simulations going on in the design of a good Diesel engine.
With hydrogen, you could in principle get the best of both worlds, and a bit better even. You could absorb in the first cycle a mixture of air and hydrogen. In the second you compress to a high pressure. Hydrogen supports much higher pressures than gasoline (it has an octane rating above 130). In the third cycle you inject a bit of diesel. That triggers its own ignition, but also the ignition of the hydrogen that's about evenly mixed with the oxygen in the cylinder.
A problem with diesel engines is that they run at a much higher temperature than Otto engines. That results in much better efficiency, but also in the oxygen reacting with the nitrogen in the air and resulting in NO2 and NO3 pollutants (and the whole Dieselgate saga with Volswagen). With the hydrogen-diesel engine, if you run the mixture a tiny bit rich in hydrogen, then you won't have enough oxygen to burn with the nitrogen, so you end up with less pollution.
However, if instead of an Otto-Diesel hybrid, you have a pure Diesel, then you need to use two injectors, one for the diesel fuel, one for hydrogen. That's a lot of added complexity.
It's not clear though if this is a pure Diesel engine or a hybrid between an Otto engine and a Diesel engine. I tend to believe it's a pure Diesel, but that would be a pitty.
In an Otto engine, in the first cycle you absorb in the cylinder a mix of air and fuel droplets, which you then compress in the second cycle, and detonate using a spark in the third cycle. In the last cycle you release the burnt gases.
In a Diesel engine, you absorb just air in the first cycle, which you then compress in the second. You can compress to much higher pressure (and temperature) than in the Otto engine, because the compressed air can't auto-detonate. You then inject fuel, which ignites immediately (no need for a spark plug). You have a slight problem: apart from the first few particles of fuel, the next ones will not find too much oxygen around, since it was already used to burn the first fuel. You solve that by insuring the geometry of the cylinder and piston is such that there is good turbulence going on. Lots of computer simulations going on in the design of a good Diesel engine.
With hydrogen, you could in principle get the best of both worlds, and a bit better even. You could absorb in the first cycle a mixture of air and hydrogen. In the second you compress to a high pressure. Hydrogen supports much higher pressures than gasoline (it has an octane rating above 130). In the third cycle you inject a bit of diesel. That triggers its own ignition, but also the ignition of the hydrogen that's about evenly mixed with the oxygen in the cylinder.
A problem with diesel engines is that they run at a much higher temperature than Otto engines. That results in much better efficiency, but also in the oxygen reacting with the nitrogen in the air and resulting in NO2 and NO3 pollutants (and the whole Dieselgate saga with Volswagen). With the hydrogen-diesel engine, if you run the mixture a tiny bit rich in hydrogen, then you won't have enough oxygen to burn with the nitrogen, so you end up with less pollution.
However, if instead of an Otto-Diesel hybrid, you have a pure Diesel, then you need to use two injectors, one for the diesel fuel, one for hydrogen. That's a lot of added complexity.
hydro-diesel: $0.48-$0.60/mile. diesel: $0.24-0.30/mile
I don't see this being viable without a significant cost reduction in hydrogen, also the storage of the hydrogen is also a problem. If this was a supplemental fuel like a NOS canister, I could see that doing something.