Cummins QSK95 engine compatible with renewable diesel
20 September 2022
Cummins announced that its Tier 4 QSK95 engine can be safely used with renewable diesel, without any negative impact to its current US EPA emission requirements or reliability.
Working with Siemens Mobility—who uses the QSK95 engine to power their Charger locomotives—Cummins undertook extensive testing and investigating of the impact of renewable diesel on their QSK95 Tier 4 fuel and aftertreatment systems through performance, emissions, and durability tests.
The fuel used for these tests was hydrogenated vegetable oil (HVO) renewable diesel. HVO can be produced by processing renewable lipid feedstocks such as vegetable oils, tallow, or used cooking oil. HVO fuels can meet the applicable diesel fuel quality standards and can be blended and used in any proportion with petroleum diesel. However, as HVO fuels are predominantly paraffins, challenges can arise if the changeover from a fuel containing significant aromatics to HVO is not properly managed—including issues related to sealing against leaks and solubility of fuel degradation products.
The Cummins tests showed that the QSK95 engine—while meeting the EPA Tier 4 emission requirements—recorded additional emission reductions with the tested HVO fuel, compared to traditional diesel in rail applications:
- NOx emissions were reduced by up to 13%, presumably due to the higher cetane number of HVO fuels (a smaller pre-mixed burn phase and thus lower peak temperatures) and their lower density (which would lengthen the injection duration and thus, more of the fuel would be injected later in the cycle). These NOx reductions seem in-line with other data for paraffinic fuels, renewable or non-renewable synthetic FT diesel.
- Diesel exhaust fluid (DEF) consumption was reduced by up to 5%. It is unclear, however, whether the DEF consumption reduction and NOx reduction would be simultaneous. One could speculate that, with a lower engine-out NOx when using HVO, tailpipe NOx could be about 13% lower while maintaining petro-diesel DEF consumption or the DEF consumption could be lowered about 5% while maintaining petro-diesel NOx emissions.
- PM emissions were reduced by up to 50%, presumably due to the low level of aromatics in the HVO fuel. Since the engine does not have a particulate filter, its PM output would be sensitive to the aromatics levels in the fuel.
Interestingly, the Cummins press release is silent on the effect of HVO diesel on fuel consumption and engine efficiency. Considering the HVO properties, it could be expected that its lower density would likely increase the volumetric fuel consumption, while a longer injection duration would also further increase fuel consumption as thermal efficiency could be lower.
The Cummins QSK95 is a 16-cylinder, 95 liter diesel engine for rail, marine, and mining applications, with power ratings of 3,600-4,400 hp (2,685-3,281 kW) at 1,800 rpm. In its US Tier 4 / EU Stage V versions, the engine utilizes urea-SCR aftertreatment for NOx control and does not use exhaust gas recirculation (EGR) or a diesel particulate filter (DPF) (Stage V standards for this engine power category do not include a PN emission limit).
Source: Cummins