Heavy-Duty Truck Emissions Performance with Low-Carbon Fuels under Euro 7 Conditions

Report no 9/26: The scope of this experimental study was to examine low-carbon fuel effects on a current commercially available state-of-the-art Euro VI step E HDV, tested under the proposed Euro 7 conditions and against Euro 7 emissions limits. In doing so, the aim of the work was to determine the gap between state of art HDV emissions performance and that required for Euro 7. As Euro 7 regulation requires the manufacturers to comply with the emission limits using all market fuels approved by the manufacturer, it was also intended to determine the effects of low carbon fuels on pollutant and CO2 emissions performance.

The testing activities were performed on a heavy-duty chassis dynamometer. The study included testing of five different diesel blends containing various amounts of the same three base fuels: EN590 petroleum diesel, EN14214 fatty-acid methyl ester (FAME) and EN15940 hydrotreated vegetable oil (HVO) as shown below:

1. Fuel A (reference): EN590 B7 Ref, 93.5 % petroleum diesel and 6.5 % FAME.
2. Fuel B: EN16709 B30, 70.5 % petroleum diesel and 29.5 % FAME.
3. Fuel C: EN590 R33, 67.5 % petroleum diesel, 6.6 % FAME and 26 % HVO.
4. Fuel D: R80B20, 80.6 % HVO and 19.4 % FAME.
5. Fuel E: EN15940 HVO, 100 % HVO.

The experimental campaign was divided into two phases. In the first phase, fuel effects of the five fuels were studied using a RDE-simulating (Real Driving Emissions) test cycle corresponding to Euro 7 conditions. In the second phase, tests were conducted over an urban driving cycle designed to be extremely demanding for the emissions control systems and beyond normal emissions compliance test regimes. In the second phase, only two fuels were tested: the most representative low carbon fuel (100 % HVO) compared to reference fuel, EN590 B7

All results were well within the Euro 7 limits, with N2O being the only pollutant close to the new limit. It follows that with overall emissions this low, the differences between other test fuels can be expected to be small. This was the case, and these results are presented and discussed in detail in the report.

The key findings of the experimental testing are summarised as follows:

• The results demonstrated that the tested state-of-the-art Euro VI Step E vehicle, with its current technology, i.e. engine and exhaust after-treatment system (EATS), could already comply with the emission limits defined in the Euro 7 regulation, over a representative simulated RDE cycle, with fuels including EN590 B7 and low carbon fuels comprising various ratios of petroleum diesel, FAME and HVO. However, the results also demonstrated that diesel-powered Euro VI HDVs can struggle with NOx mitigation under extreme conditions, in particular where the vehicle is subjected to generally low loads (therefore low EATS temperature below efficient pollutant conversion thresholds) when combined with rapid and heavy transient driving. This phenomenon could potentially be managed by employing catalyst pre-heating measures.
• N2O was the only exhaust component close to or above the declared Euro 7 limit with a final conformity factor between 0.65 to 1.01. However, N2O is predominantly generated in the EATS and different catalyst materials can be employed to manage N2O.
• Low-carbon fuels containing paraffinic diesels were found to reduce TP (tailpipe) CO2 emissions and increase powertrain efficiency simultaneously, demonstrating that such low-carbon fuels based on various combinations of FAME and HVO can provide tailpipe as well as WTT carbon reduction benefits.
• Fuel effects on pollutant emissions at tailpipe were immeasurably small due to the highly efficient emissions control technology of modern IC engines, with closed loop control mitigating fuel effects.

Overall, the results of this study show that there are minimal gaps between the emissions control performance of the state-of-the-art Euro VI step E HDV tested and the performance required to fulfil Euro 7 requirements due to highly effective and mature exhaust after-treatment technology for IC engines. Furthermore, a range of low carbon fuels function well in this technology, with no demerits and some benefits in engine-out NOx emissions, cold start HC and CO emissions, TTW CO2 reduction and improved efficiency.