There's one small issue with diesel engines. Diesel exhaust fumes cause cancer: http://scienceblog.cancerresearchuk.org/2012/06/14/diesel-fu...

Take a look at the list of Category 1 carcinogens, at https://en.wikipedia.org/wiki/List_of_IARC_Group_1_carcinoge... .

Also on that list are 'Alcoholic beverages', 'Salted fish (Chinese-style)', and 'Wood dust'.

The article mentions that particulate is in a classification that is known to cause cancer, however, the article admits that "IARC isn’t in the business of telling us how potent something is in causing cancer – only whether it does so or not."

The amount needs to be identified, because it could be similar to the radiation levels in bananas... There is some, but it may not be enough to be deadly.

I mentioned this mostly as a reply to:

[3]The caveat is that petrol gas emits particulates at a smaller micron level, unnoticeable to the naked eye, and may actually be of greater concern to the general public.

The diesel exhaust fumes are proven to be worse than the petrol engines in at least one respect - health.

Maybe if every truck on the road and a lot of the cars ran on bananas and not on diesel, then I would be concerned about the radiation levels in bananas.

Moreover in the place where I live people are allowed to remove their car DPFs which makes things even worse.

They're also easier to stop/start, esp on long downhill stretches.

Does all of this include Hybrid engines or just more traditional gasoline engines?

The thing to remember is that hybrids and electrics tend to moderately trade off emissions for an increase in toxic waste from production. Neodymium for motors, tantalum for capacitors, lithium for batteries - all of those are bad news bears for the environment. Even stuff like copper isn't particularly awesome to produce. All other things being equal (mileage, emissions, etc), you should prefer the vehicle with a simple aluminum frame and engine over the high-tech wundercar because the impact of producing and disposing of it is lower.

To the actual question - yeah, diesels running on biodiesel actually produce less GHG emissions than even hybrids. Ultra Low Sulfur Diesel is pretty close but just a bit above hybrids. The National Academy of Sciences published a study back in 2010 on the topic. The report itself is paywalled but there's a copy on the Arkansas state website. I snapped an image of the chart for ease of viewing.

Note that ULSD was only introduced in the US in 2010 (2006 for Cali). The Euros have had it for quite a bit longer. So when you're reading studies, if it predates 2010 and it doesn't specifically say ULSD or Biodiesel then you should disregard it, because the new fuels are vastly cleaner and the playing field has shifted dramatically as a result. Biodiesel is often notated as something like B100, B85, or BD20 denoting the percentage of biodiesel in a mixture with fossil diesel. Pure B100 has a fairly high gel point and can cause problems starting in cold areas, so these mixtures include a fraction of ULSD to lower the gel point.

http://imgur.com/FEOo1zB

http://1.usa.gov/1gO9jPL

"Despite lower carbon dioxide emissions, diesel cars may promote more global warming than gasoline cars."

http://news.stanford.edu/pr/02/jacobsonJGR1023.html

http://www.sciencedirect.com/science/article/pii/S0301421507... (available without cost from http://earthjustice.org/sites/default/files/black-carbon/bou... )

"Jacobson (2002, 2005) suggested that, despite their lower fuel efficiency, gasoline cars were better for climate than BC-emitting diesel cars. However, Jacobson’s analysis relied on radiative forcing (RF) and climate equilibrium calculations, which is artificial and possibly misleading because any policy or technology will only be implemented for a finite period of time"