[vvanders]

Yes, however common diesel fuels tend to be higher in NOx and particulates.

My understanding is that because gasoline is refined to a higher degree it burns a fair bit cleaner in similar environments(and also makes it a PITA to store for more than a few months).

[edit]

We've got a pair of tractors around the house here, '81 diesel(pre-emissions), and '47 gasser.

I can tell you which one I prefer to run from an exhaust perspective, the diesel may have torque and is a dead-simple engine but you don't want to be downwind of it when cutting heavy brush.

[toast0]

NOx emissions from a diesel engine are from atmospheric nitrogen and oxygen, not from the fuel. I welcome further clarifications, but my understanding is that this engine will not produce NOx like a standard diesel because the fuel/air mix will be tightly controlled like in a gasoline engine, and temperature and pressure will be significantly less than a standard diesel. Additionally, it seems the timing of the fuel injection will be much earlier than a diesel, resulting in more complete air/fuel mixture; this is possible because gasoline has a higher ignition temperature, so fuel can be injected early and ignition won't happen until the compression stroke; diesel fuel would ignite during injection regardless of where in the cycle.

[ajross]

I'm struggling with the same reasoning: NOx is the result of high combustion temperatures, which is a pure function of the compression ratio (and fuel mixture), which is the thing that defines the high efficiencies you can get with a diesel cycle.

The argument in the linked wikipedia entry is that combustion temperatures are lower in this cycle because the better fuel/air mixing means it can burn much leaner and thus at a lower temperature. But a leaner mixture means lower power for a given displacement too, which means lower efficiency than a comparable traditional diesel (which are already hard-pressed to see gains like the 40% claimed against well-tuned gas engines).

Honestly the whole thing sounds very snake oily to me. I don't deny that it's possible such a thing could be tuned to operate as well as a traditional engine, but... it sounds awfully fiddly. I'd want to see numbers from a production engine in a real car before placing any bets. Electric continues to look like a much better bet to my eyes.

[tadfisher]

I don't buy the wikipedia argument either, but I do believe the homogenous charge mixture will burn at a lower temperature for a given compression ratio than the equivalent stratified charge.

Throwing f/a into the mix, the HCCI mode is apparently only active during low-power cruise, so the lean mixture is fine. The Mazda innovation is controlling the changeover from HCCI to SI when more power is demanded.

[vvanders]

According to wikipedia the fuel can be a large source of nitrogen for NOx: https://en.wikipedia.org/wiki/NOx#Fuel