Replacement of diesel with compressed natural gas could significantly reduce tailpipe CO2 emissions in heavy-duty trucks, even once realistic routes and road elevations in a mountainous region like British Columbia are taken into account, researchers have found. And if advanced fuel-efficiency technologies that are currently on the lab bench but yet to be commercialised are adopted by trucks using CNG as a fuel, these emissions savings can climb much further.
Research that finds substantial savings for CNG trucks over diesel is nothing new. A 2015 study found light-duty CNG trucks can produce 34 percent fewer emissions than their diesel equivalent, and a 2013 study using the same methodology found a 15 percent reduction for heavy-duty trucks.
The problem is that most previous studies employ computer models that have not paid much attention to how the emissions profile of a truck changes depending on what sort of routes are travelled. So these estimates of the benefits of CNG over diesel can become suspect.
A long, steep hill climb alters things considerably compared to a ‘drayage’ route (ferrying goods short, flat distances, for example from port to warehouse). Vehicle technologies also toss things up. A CNG truck with an 11.9L engine will produce almost a third less CO2 in a drayage run than a 15L diesel truck. But put those two trucks on a hill, and now that same CNG truck will produce 11 percent more CO2 than the diesel truck. This is expected to be alleviated with larger engine sizes for CNG trucks that are soon to come to market.
But there remains a lot of uncertainty. Real-time emissions measurements on the road with actual trucks can go a long way to reducing this uncertainty. But these are really expensive to carry out. So modelling is often used instead, but as we have seen, this can lead to oversimplification
So the researchers with the Pacific Institute for Climate Solutions developed a new model that could take into account road gradient, as well as compare current and theoretical engine technologies. A handful of simulations by other researchers had included road gradients, but none had considered the kind of steep road grades of up to eight percent found in BC. To do this, the PICS researchers included elevation profiles from Google Earth in their models.
They found that even under these more realistic scenarios with current technologies, replacement of diesel with compressed natural gas could reduce tailpipe CO2 emissions by 13-15 percent in heavy-duty trucks.
Trucks employing advanced vehicle technologies covering improvements to weight, aerodynamics, engine efficiency and rolling friction meanwhile could cut their emissions by up to 35 percent over conventional diesel vehicles in the near future and 51 percent over the long term.
If the same ‘future-concept’ technologies are applied to diesel trucks, they too enjoy impressive emissions reductions, if not quite as much as CNG: 23 percent in the near term and 42 percent in the long term compared to conventional diesel trucks.
Energy economist Mark Jaccard helped design BC’s carbon tax, and he still supports it. But he questions just how politically viable a stringent tax—at the level needed to meet climate targets—can really be. So he also continues to explore how other policies that the public find more acceptable could work.