Researchers from Istituto Motori - CNR in Italy and Eni report in a paper in the journal Fuel that blends of hydrocracked fossil oil (HCK) and Hydrotreated Vegetable Oil (HVO) as diesel fuels deliver fuel consumption (FC) and CO2 savings based on the NEDC cycle.
The researchers said that, given the strong similarity in combustion system design between Euro 5 and Euro 6 engines, the estimated trends can be considered valid also for Euro 6 vehicles equipped with the same class of engines. In a next step, they plan to validate these results with the WLTP and RDE emission tests.
Hydrotreated Vegetable Oil (HVO) has become an attractive industrial-scale alternative to ester-type biodiesel. It can be produced from many kind of non edible vegetable oils, animal fats, waste oils and consists of a mixture of paraffinic hydrocarbons in diesel boiling range, free of sulfur, oxygen and aromatics. Regardless of the feedstock, neat HVO has high cetane number and low density. Its bulk modulus and material compatibility is similar to petroleum diesel. Good cold properties can be obtained by adjusting the isoparaffin/normal paraffin ratio in the isomerization step of the production process. Adequate lubricity can be achieved by treating with lubricity improver additives. Differently from FAME, the HVO properties do not depend on the adopted production feedstock and many proprieties are very similar to the gas-to-liquid (GTL) and biomass to-liquid (BTL) diesel fuels produced by Fischer-Tropsch (FT) synthesis. HVO based fuels can be used without affecting fuel logistics, engine and exhaust after-treatments.—Napolitano et al.
The researchers recently published a detailed analysis of the correlations among HVO/HCK based premium fuel properties, engine operating conditions and global NEDC emissions in real modern automotive diesel engines. That study showed a clear positive impact of the use of HVO/HCK blends (at different blending ratios) on pollutant emissions. Benefits on FC and CO2 emissions could be estimated, but their magnitude was within the limits of measurement uncertainty.
By the way, an improvement of a few percentage points in terms of FC and CO2 emission reduction still represents a significant goal in consideration of the high investment costs necessary to achieve the next CO2 saving targets.—Napolitano et al.
In their latest study, the team used a four-cylinder Euro 5 automotive engine, making transient tests on both MVEG-B (NEDC) and ARTEMIS cycles. They used three experimental fuels with varying HVOs fraction in a HCK base along with a fourth commercial fuel as reference for baseline tests.
The fuels were a commercial EN590-compliant diesel fuel (D1), a diesel fuel formulated with streams from a hydrocracking process (D2) and two blends of HCK streams with 15%v/v (D3) and 30%v/v (D4) HVO respectively. All fuels were FAME-free.
Among the results of the test:
The use of blends of 15% and 30% of HVO in HCK base gives an average FC reduction of about 1% ± 0.25 and 1.46% ± 0.25. Thanks to a favorable LHV/Density ratio of the HCK with respect to the reference fuel and HVO, the blend of 15% HVO in HCK offers also a reduction of the volumetric FC of about 0.6% with respect to the reference one;
The FC reduction on a mass basis is higher than the simple fuel LHV increment. This means that the engine net efficiency is improved and, for the blend of 30% of HVO in HCK, the CO2 emissions are lowered up to about 2% over a mileage of 1000 km; and
The better engine efficiency burning the HCK-HVO blends depends exclusively on the thermal efficiency improvement at low/partial loads due to the increase of the cetane number of the blend.
In conclusion, the use of HVO and HCK in the diesel fuel formulation can be exploited by automotive diesel engines to optimize emissions, including CO2, (as demonstrated in previous research), as well as, mass and volumetric fuel consumption.—Napolitano et al.
Pierpaolo Napolitano, Chiara Guido, Carlo Beatrice, Leonardo Pellegrini (2018) “Impact of hydrocracked diesel fuel and Hydrotreated Vegetable Oil blends on the fuel consumption of automotive diesel engines,” Fuel, Volume 222, Pages 718-732 doi: 10.1016/j.fuel.2018.02.097