HVO and biodiesel are both renewable, plant- or waste-derived alternatives to diesel, yet these two fuels are quite different. One of the key differences is the production methods used; biodiesel is made from vegetable oils, animal fats, or used cooking oils using a process called transesterification, which converts the oils into Fatty Acid Methyl Esters (FAME), while HVO is produced using hydrotreating as described above. 

As a result of these different production methods, HVO is a pure hydrocarbon fuel that closely resembles diesel while FAME biodiesels can contain 10 – 12 percent oxygen, leading to higher oxidative instability. Additionally, biodiesel is prone to gelling at low temperatures (-5°C to ~15°C depending on the feedstock used). Together, these two characteristics mean that FAME biodiesels cannot be considered a drop-in fuel since the engine may be incompatible or need modifications to run the biodiesel, or a change in maintenance procedures may be required. Additionally, FAME biodiesels generally have a shorter shelf life than HVO due to their higher susceptibility to oxidation.
 

Diesel is often blended with FAME biodiesel, which offers benefits such as reducing lifecycle CO2 emissions, improving lubricity to reduce engine wear, and lowering particulate emissions versus using unblended diesel. While up to a 20 percent blend of biodiesel fuel by volume (B20) is acceptable for use in many Perkins’ engines, using a blend above B20 can lead to bacterial growth that impacts maintenance of the fuel system. HVO does not have this same consideration and can be used in a pure state or at any EN590 diesel blend level

Since HVO is a pure hydrocarbon, it is backwards compatible with older engines and can be used in most engines manufactured since the early 1990s. However, since diesel engines built after 2007 are required to run ultra-low-sulphur diesel (ULSD), we will focus our comparison of the characteristics of HVO to ULSD.

Feedstock Source and Sulphur Content

One of the key differences between HVO and ULSD is the feedstock source. As mentioned, the source of HVO is organic vegetation either as a virgin or secondary source. Either way, this is a renewable and sustainable feedstock. Since ULSD is a fossil fuel, the feedstock is crude oil. As a result of these different feedstocks, HVO contains virtually no sulphur, resulting in almost zero SO2 emissions during combustion. Even though ULSD has a sulphur content of 15 ppm or less, which is significantly lower than traditional diesel that could have been up to 500 ppm, there are still SO2 emissions occurring when using ULSD. 

Storage

Due to the consistency and chemical stability of HVO, it is resistant to a variety of factors such as oxidation and microbial growth, making it suitable for long-term storage without degradation. Since ULSD can oxidise and is more prone to moisture absorption that can cause microbial growth, it must be carefully managed when stored and has a much shorter shelf life, especially when the ULSD has a high FAME content (B20+).

Life Cycle Emissions

Using HVO can significantly lower life cycle emissions from well-to-wheel for multiple reasons. First, HVO can be produced locally from available feedstocks, leading to a reduction in the emissions associated with the transportation of raw materials and the fuel itself. 

Second, the feedstocks for HVO are derived from biological sources that absorbed CO2 as they were grown. Therefore, when HVO is burned as a fuel and CO2 is released back into the atmosphere, the majority of these emissions can be accounted for with the CO2 absorbed during the feedstock’s growth, resulting in a closed carbon loop. Or, if the feedstock comes from organic waste materials, less materials are potentially transported to landfills.

Recently, our engineers worked on a project in cooperation with Jubaili Bros, an OEM using Perkins engines in their diesel generator sets, to research the impacts on performance and emissions when using HVO for a generator set application running a Perkins® 1103 Series engine. The testing was completed at Perkins Engines Company Ltd, Peterborough UK between January and July 2024. The goals of this project were to:

• Demonstrate the suitability of using EN15940 HVO as a drop-in replacement for diesel, specifically an EN590 ULSD
• Conduct back-to-back testing to directly compare HVO to diesel, demonstrate benefits of using HVO versus diesel, and confirm that there are no detrimental impacts of using HVO.
• Provide customers with confidence in performance, efficiency, operation, and service life with the use of renewable fuels.
• Determine if the source of the HVO has any significant impact on performance, emissions, and efficiency.

Test Setup
At a high level, our testing involved running a 1,000-hour high-load generator set durability cycle test while executing target performance tests every 250 hours as the engine was aging (Figure 1). Figure 1

The periodic performance tests we ran at 0, 250, 500, 750, and 1,000 hours included load acceptance, fuel consumption, and emissions testing. For the load acceptance test, we tested to ISO 8528 standards against G2 test cycle, which specifically defines performance standards for generator sets, using automated test scripts through a load bank with a pass or fail result (Figures 2 and 3).

For the fuel consumption testing, we ran the engine at steady-state load conditions for 30 minutes after conditioning, with testing starting at the highest load and working down the load to maintain consistent engine temperatures where possible. An auxiliary 20 litre fuel tank was weighed before and after running each load point, to 1 gram resolution with a maximum error of 3 grams; corresponding to a maximum 0.2 to 1% error based on fuel consumption over these tests (Figure 4).

For the emissions testing, we used a portable emissions measurement system (PEMs) to measure tail pipe emissions including CO₂, CO, hydrocarbons (HC), and NOx (Figure 5). We also performed soot particle measurements using an AVL 483 micro soot sensor and measured exhaust mass flow.

At the end of the 1,000-hour load test, we then performed the target performance tests using HVO from three additional suppliers to determine if the source of the HVO would have any significant impact. Some additional notes on the HVO we used:

• All HVO complied with the EN15940 standard for paraffinic diesel fuels and was sourced from various suppliers in the UK
• HVO 1 was used for the 1,000-hour high-load generator set endurance cycle running and performance testing and baseline tests against EN590
• HVOs 2,3, and 4 were used for the alternative supplier tests for back-to-back comparison

º Averages of all samples – 2 different methods have been used to test density giving a possible 1 percent variation.
¹ Using 4-square method ASTM D4737-21.
² Using ASTM D6304 - Max value seen (Average).
³ Mean Wear Scar Diameter – ISO12156 against 320µm Repeatability = 69.53 Reproducibility = 97.342.
* Values from start and end of HVO IBC - 1 (lower number being at the end of the IBC).

Beyond these tests, we also performed noise and vibration testing to see if there were any differences in the noise or vibration levels when running HVO in the engine. We performed a comparison of EN590 and HVO at 0 hour and then reran the testing with HVO at 1,000 hours. The main goal of this testing was to determine if a user might think something was wrong with the engine if the noise and vibration levels were significantly different when running HVO versus EN590.

Overall, this testing supported our hypothesis that HVO could be used as 1-1 drop-in replacement for EN590 diesel in the generator set with no specific engine conversion process needed when HVO is used for the first time or thereafter. The tanks and filters also do not need to be cleaned when switching between HVO and diesel. Other high-level results of the testing included:

• No significant difference in performance between the EN590 and the HVO EN15490
• Both engine emissions and fuel consumption remained consistent throughout testing
• The ISO 8528 load acceptance testing verified that the generator set could handle the intended operational loads reliably
• The noise and vibration testing revealed there was no difference in noise or vibration levels when running HVO EN15490 versus EN590

Digging down into our results, regarding fuel consumption, our testing showed that HVO EN15940 fuel consumption averaged about 2 to 2.5 percent (max 3.7 percent) higher than EN590 by volume (Figure 6). This difference is likely explained by the fact that EN590 has ~6 percent higher volumetric density, which is partially offset by its lower energy density compared to HVO EN15940. These results were in line with our expectations and remained consistent throughout testing.

Additionally, our emissions testing revealed that when running HVO, there were similar tail pipe emissions for CO, CO₂, NOx, and soot levels, but a noticeable reduction in tailpipe HCs as shown in Figure 7. We believe this reduction in tailpipe HCs was due to the increased paraffinic, and reduced aromatic, proportion of HVO compared to diesel. This lowers the fuel’s final boiling point, which promotes earlier, and more complete, combustion that reduces the partially combusted HCs seen in the exhaust gas. This correlates with the increased cetane number of the HVO.

Through our high-load endurance testing, we saw that during the first 500 hours of running, the engine speed at the 110 percent load point gradually decreased over time (Figure 8) which can occur as a new engine is run-in. Before running the second 500 hours of testing, we completed a ‘high-idle adjustment,’ which brought the frequency/engine speed back up to the higher 50.8 Hz/1,525 RPMs for the start point of the second part. This was successful and we saw only a slight speed reduction during the second 500 hours of testing as shown in Figure 8.

Regarding the service life of the engine when running HVO, we found that engine performance remained acceptable through the 1,000-hour test period. Oil condition remained acceptable, service intervals were unchanged, and based on a visual assessment, the engine condition looked as expected as well (Figure 9).

Additionally, the noise and vibration testing revealed the following results, as shown in Figure 10:

• Similar amplitudes for vibrations between HVO and EN590
• Similar amplitudes for vibrations between 0 hour and 1,000 hours with HVO
• A slight decrease in sound power level with HVO relative to EN590
• No noticeable difference in sound levels between 0 hour and 1,000 hours with HVO

For the final part of our testing, we aimed to determine if the source of the HVO could have any significant impact on performance, emissions, and efficiency. No significant differences in performance, emissions, or fuel consumption was found between the variants. Fuel consumption for each variant was consistent, with approximately 1.5 percent variation at 100 percent load (Figure 11).

Across all variants, no significant changes were observed except for an increase of soot noted when testing HVO 2 (Figure 12). We repeated this test to eliminate the possibility of a measurement error and came up with the same result. In general, this test demonstrated that using EN15940 fuels from different sources offers a level of stability and equality.

While running a generator set on HVO provides similar performance to diesel, there are several ancillary benefits OEMs, and their customers, can experience by making the switch. First, substituting HVO for petroleum-based diesel reduces life cycle greenhouse gas emissions, while maintaining similar tailpipe greenhouse gases emissions as traditional diesel.

Additionally, having the ability to highlight that your equipment’s engines can run HVO can be a competitive advantage as you may have the opportunity to differentiate your company and win more business. Plus, having the confidence to know you can switch your engine to HVO, or any HVO/diesel blend, also provides greater flexibility in fuel sources as well as supply chain resilience. Having an alternative fuel option to switch to when needed can reduce the risks associated with price volatility and supply chain disruptions that can happen with fossil fuels.

As an OEM serving the power generation or heavy machinery industries, you likely have customers looking to implement more sustainable or flexible power solutions while maintaining performance and fuel efficiency. As demonstrated by our rigorous testing, this can be achieved by using HVO as a drop-in alternative to traditional diesel in a Perkins engine. The compatibility of HVO with existing infrastructure offers OEMs and their customers the opportunity to focus on today’s evolving energy landscape related while increasing operational flexibility and supply chain resiliency.

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