For our discussion this month, we turn to the Diesel Technology Forum, whose executive director, Allen Schaeffer shares insights on emission reductions, the VW settlement funds, and renewable diesel.

1. How do the emissions of the latest diesel engines compare to those of propane and compressed natural gas (CNG)?
Diesel, gasoline, CNG, propane, and other fuels are all held to the same stringent standard. Diesel meets that standard today with the added benefit of a completely intact fuel infrastructure as opposed to other alternatives.

While some alternatives have received a lot of media attention over the past couple of years, the emergence of clean diesel technology and fuels have quietly and effectively moved forward in all transportation sectors. For example, the Clean Air Task Force’s “Clean Diesel versus CNG Buses” (2012) analysis found: “According to EPA’s MOVES emissions model a 2012 model year diesel bus emits 94% less NOx per mile, 98% less PM, and 89% less HC than a model year 2000 diesel bus. A model year 2012 CNG bus emits 80% less NOx, 99% less PM, and 100% less HC than a model year 2000 diesel bus.”

2. Are there reasons to be optimistic about what’s ahead for diesel engine technology?
Today, diesel technology is the powertrain of choice for commercial vehicles, including school buses. According to the latest vehicle-in-operation statistics, diesel powers 95% of all school buses. While alternative fuels, including CNG and propane, have made some inroads, we are confident that diesel will still remain the powertrain of choice for school bus fleets.

Diesel is the most efficient and cost-effective fuel for school buses. Conservatively, it provides 25% to 30% better mileage than comparable natural gas buses.

3. How do you expect the VW emission scandal and its settlements to impact the use of diesel in transportation?
The $3 billion fund was created for the sole purpose of reducing NOx emissions. Whether it is replacing a school bus, larger commercial vehicles, or even switch locomotive engines, more NOx emissions can be reduced immediately — not years or decades from now — by investing in clean diesel relative to other technologies.

As each state begins deliberations on how to spend their portion of the VW environmental mitigation trust funds, their project selection process should be guided by four basic criteria:

1. Projects must target the largest sources of NOx emissions.
2. Technology choices must be verified as effective in delivering NOx reductions.
3. Projects should emphasis the timeliness of the actual NOx reductions.
4. Projects should maximize the use of funds available by selecting those that deliver maximum NOx reductions per dollar invested.

When these important criteria are applied, it’s clear that in nearly every case, upgrading, replacing, or repowering engines to new clean diesel technology would deliver more clean air for the dollar, faster, and would benefit more residents.

4. What’s happening with the Diesel Emissions Reduction Act (DERA) program?
DERA is going through what it has frequently experienced in past proposed budgets. Several times, the Obama administration proposed “zeroing out” the program in its proposed budget only to have Congress work on a bipartisan basis to restore funding. This year is no different. The Trump administration proposed to either eliminate the program or reduce funding substantially. On Capitol Hill, the program is seen as highly effective in making the most of limited federal spending to achieve many environmental benefits. The school bus retrofit program within DERA is specifically highlighted as a highly effective program. … For this reason, we expect Congress’ bipartisan support will continue this year and in the future.

5. What is renewable diesel, and do you see it catching on?
Renewable diesel fuel is similar to traditional biodiesel in that it is derived from similar feedstocks. However, a different chemical process is used to derive a final product that is chemically very similar to petroleum diesel fuel. … Renewable diesel fuel is considered an advanced biofuel by the U.S. EPA. That means it is capable of reducing greenhouse gas emissions by more than 50%. In fact, some studies conclude that the fuel reduces emissions by 90%.

Right now, communities like San Francisco, Oakland, and San Diego are moving to renewable diesel fuel for immediate and significant emissions reduction without the need for new and costly fuel infrastructure systems.