Do natural gas trucks produce more or fewer emissions than diesel trucks?

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By Rodrigo Baranna – Consultant

Transport & Environment (T&E) recently published an analysis titled “Do Natural Gas Trucks Reduce Emissions?” ^[1]. T&E analyzes the results of a study conducted by TNO ^[2] in the Netherlands comparing the emissions of three models of liquefied natural gas (LNG) trucks with four models of diesel trucks. The article’s conclusion is unequivocal: According to T&E, the claims made by heavy-duty truck manufacturers regarding the emissions benefits of Natural Gas for Vehicles (NGV) are false.

In the TNO study in question, titled “ Emissions Testing of a Euro VI LNG-Diesel Dual-Fuel Truck in the Netherlands ", the results show that The three LNG models do not achieve the announced reductions in local emissions, compared to the average for the four diesel models. In some cases, LNG emits significantly higher levels than the average for diesel, such as in urban areas, where all three models recorded NOx emission levels significantly higher than the average for diesel trucks. In terms of greenhouse gas emissions, the three LNG models perform slightly better than the average for diesel models based on a tank-to-wheel analysis. Adding to this the emissions associated with When it comes to fuel consumption, no one type of engine has a clear advantage over another. However, can these results be generalized to all CNG models? The participants in the Équilibre project and IFSTTAR have published an analysis of the T&E report ^[3], in which they call into question certain technical aspects, results, and conclusions. Their main arguments are:

• Statistical validity: the conclusions would be based on a very small sample, both in terms of the models analyzed and the kilometers traveled;
• Variability in test conditions: Since NOx emissions are highly sensitive to speed fluctuations, an indicator measuring traffic conditions should have been monitored. Furthermore, particulate emissions were measured in the laboratory for diesel models and on the road for LNG models.

The findings of the Équilibre project on emissions from natural gas-powered trucks are summarized to highlight the wide variation in results based on several technical characteristics, particularly the type of natural gas fuel. LNG-powered models do not perform the same as compressed natural gas (CNG) models. Thus, Conclusions should be drawn for each model separately—LNG or CNG—and not generalized to natural gas vehicles as a whole.. But isn't there a general aspect of natural gas vehicle (NGV) engines that is independent of the specific model in question? There is a convergence point between the TNO study, the T&E analysis, and the report by the Équilibre project and IFSTTAR: In terms of climate impact, CNG (compressed natural gas) does not reduce carbon emissions in road transportation. Only renewable gas—particularly biomethane used as bio-NGV—can reduce greenhouse gas emissions compared to the use of diesel. The question to ask is that of the transition :

• Is it appropriate toto use natural gas, which is a fossil fuel, as an energy transition solution for road transportation, to pave the way before renewable gas is widely adopted?
• Furthermore, given the Renewable gas production potential: Will there be enough to decarbonize current gas uses?, particularly in the building sector, electricity generation, and industry?

Article written by Rodrigo Baranna – Consultant

Sources: ^[1]Transportation & Environment^[2]TNO^[3]The Équilibre Project and IFSTTAR