While common rail CR is a great technology for Diesel fuel - it hard to trim for alternative fuels.
The high pressure pumps don't like the high viscosity of alternative fuels. The tolerances are to small in the injectors etc... yeah
That doesn't surprise me. CR tech being direct injection is highly dependent on the fuel air interaction. Change the fuel characteristics (eg viscosity and ease of evaporation) and the system is out of kilter.
Further, NOx and particulate actually got worse with early CR, a mechanical injected Euro 2 emission Diesel - those put out nice smoke the tailpipe - but it was all large particulate. It sank down to the ground rather fast and your lungs are pretty adapt in filtering it out. Then with all Euro 3 and 4 stages - they just made the particulate smaller so that the detectors of that time couldn't register them anymore.
Good point re the smaller particles remaining airborne for longer. Also, the smaller the particle, the further into the human body it can travel.
While decreasing fuel economy... yes more power - but less economic.
Reduced CO2 (which improves fuel efficiency) and reduced NOx are mutually exclusive. Gain on one, lose on the other.
The most efficient Diesel cars where in the 90s and early 2000s. 3L/100km (78 MPG) for small cars and 4L (59MPG) for large sedans and station wagons were common. You could drive a VW bus with 6L (40MPG) and Mercedes Sprinter with 7L (34MPG) Then emission standards where tightened and we ended up with very few cars available for sale today which getting below 30MPG... PROGRESS
Lets burn perceived cleaner - but need double the amount of fuel. And it did absolute nothing to clean up the air in cities.
We have to be careful here that when we view 90s diesels as fuel efficient we aren't overlooking that they were largely gutless until the advent of CR. For sure though, the latest NOx reduction measures have reduced fuel efficiency.
Despite a noticeable drop in air pollution from road transport in 2020 due to COVID-19 lockdown measures, breaches of European air quality standards remain a common occurrence across the European Union (EU), according to the EEA briefing ‘Europe’s air quality status 2022’. The briefing was done...
www.nilu.com
Some of the problems in cities is due to road planning / traffic calming. Slow a diesel down to a crawl when it then acceleartes particulate emissions will be high before the turbo spools and then NOx emissions will be when it does.
Also, re-mapping (reinstating the torque the OEMs had to dial out to pass NOx legislation), EGR, DPF, swirl flap, Adblue deletion are not helping. In the UK enforcement is lax and it is leading to cars being excluded from cities.
Why? now we got Direct Injection Gasoline engines, which are not subject to Diesel particle and NOx testing - which are more fuel efficient but produce particulate and NOx.... lol Sorry for the rant.
https://www.sae.org/news/2014/10/attacking-gdi-engine-particulate-emission
All what the standards did - was decrease the fuel economy of Diesel and make Gasoline burn dirty... Well intended but bad outcome.
To be fair, the fuel economy of SI engines has improved with the adoption of GDI. But, along with turbocharging they are heading down the same path as diesels - ie higher NOx and particulate emissions and much greater complexity.
My good old port inject Vortec 5.7L might be one of the cleanest burning engines out there.
I'll see your port injection Vortec 5.7l and raise you a Vortec 5.7l running on LPG (propane)....