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Study suggests GTL-naphtha-gasoline-ethanol blends can function as well as gasoline with lower emissions

Results of a study by a team from the University of Birmingham (UK) and Shell Global Solutions suggest that blends of gasoline with gas-to-liquids (GTL) naphtha can perform comparable combustion and full power output to conventional gasoline, with less than 2% difference in normalized ISFC (indicated specific fuel consumption) and gaseous emissions similar to, if not lower than that of conventional gasoline. A paper on their study is published in the journal Fuel.

The GTL Fischer-Tropsch process produces GTL diesel (the cleaner combustion and emissions qualities of which have been well studied), GTL naphtha, GTL kerosene, GTL normal Paraffin and GTL base oils. GTL naphtha mainly contains C4 to C11 hydrocarbons with a high proportions of straight chain paraffins. Although it has a consistent quality and near-zero sulfur and heavy metals, GTL naphtha has a low octane rating, making it unsuitable for blending in gasoline. (GTL naphtha currently is used as an alternative high-quality feedstock for plastics.) However, that low octane rating can be addressed by using ethanol as an octane booster.

The introduction of bio-ethanol as a blending component has made the octane rating of GTL naphtha a less limiting factor because ethanol has a high octane rating. However, currently there is little knowledge available about the performance of gasolines containing GTL naphtha in spark ignition engines.

In this study, four gasoline fuels containing up to 23.5 vol.% GTL naphtha, three of which were close to being EN228 compliant, were tested in an AVL state-of-art single cylinder gasoline research engine. … The focus was on the assessment of full load combustion characteristics and emissions of these new gasoline fuels with GTL naphtha.

—Wang et al.

The reference fuel was a typical EN228 compliant gasoline; the four test fuels had similar octane rating with Fuel A (the reference). Fuel B contained 7.3 vol.% GTL naphtha but no ethanol. Fuels C-E were blends of various refinery streams, GTL naphtha (12.8–24 vol.%), and ethanol (5–20 vol.%). Fuels B-D were almost EN228 compliant; however Fuel E had an oxygen content of 7.2 wt.%, which exceeded the EN228 upper limit of 3.7 wt.%.

Two modern engine configurations, a boosted direct injection (DI) and a port fuel injection (PFI), were used. The tests were conducted under full load conditions in the engine speed range of 1000–4500 rpm.

In addition to the findings on combustion and gaseous emissions, the researchers also found that compared to the conventional gasoline, lower particulate emissions were observed in gasoline fuels containing up to 15.4 vol.% GTL naphtha and 10 vol.% ethanol.

In this study, due to the limited amount of GTL naphtha available and the time constrain, less than six repeats were conducted for each fuel; therefore, no robust statistical significance analysis can be provided. Additional repeat tests on this engine and further tests on a wider range of engines/vehicles would be required to generalize the validity of these findings.


  • Chongming Wang, Jasprit Chahal, Andreas Janssen, Roger Cracknell, Hongming Xu (2017) “Investigation of gasoline containing GTL naphtha in a spark ignition engine at full load conditions,” Fuel, Volume 194, Pages 436-447 doi: 10.1016/j.fuel.2017.01.042

  • Rockstroh, T., Floweday, G., and Wilken, C. (2016) “Options for Use of GTL Naphtha as a Blending Component in Oxygenated Gasoline,” SAE Int. J. Fuels Lubr. 9(1):191-202 doi: 10.4271/2016-01-0879


Dr. Strange Love

Forget about testing it in different ratios with current fuels. We don't want that. Ideally, your source is bio-gas from Waste with Ethanol or some other high oxygen equivalent octane booster. Tell me when you are ready to Market your setup. I can help you find buyers.


@ Dr. Strange Love

The distillation unit in a refinery (even a bio-refinery) always produces a range of chemicals. [It can be tuned somewhat to get a peak of production in that range but you'll always get some of the other stuff.] If they don't find a use for all the produced chemicals they are just throwing money away.

That's all they are doing here, finding more uses for the chemicals they get out of the GTL Fischer-Tropsch process.

Dr. Strange Love

ai vin. I agree. I understand that this is a learning opportunity for these fellow researches. When we learn, there is no waste of time.

A Segway. I get frustrated with the way our kids are taught in the school systems these days too. It's an every more challenging curriculum geared toward Testing. Teachers have no flexibility and the kids are not allowed to Explore Intellectually like we could.


Shell has done a good job with GTL, Pearl is on example of it on a large scale. Many ways to fuel our transportation, bio DME for trucks, buses and ships, bio synthetic jet fuel for planes.



I too was once a supporter of using bio DME for trucks but I since gone off the idea. When used as a diesel fuel, DME provides reduced PM and NOx emissions, but increased CO and HC. However preliminary studies in the 1990s concluded that it should be possible to achieve ULEV emissions using a properly designed DME-based fuel injection system with an HSDI engine and an oxidation catalytic converter.

Other factors are more problematic. It has a lower energy density AND specific energy than diesel so we'd be burning more of it.

Plus: The physical properties of DME (density, viscosity, lubricity, etc.) are so different from the diesel fuel that the entire fuel system must be redesigned. While it seems clear that DME, like perhaps some other alternative fuels, would be able to produce much larger emissions reductions than it is possible with diesel fuel, the emission benefit comes at a price of a specific level of complexity of the fuel storage and injection system, including the need to carry a pressurized fuel tank onboard the vehicle. Furthermore, it is not clear that the apparently inherent emission advantage of DME can offset the fuel’s lack of established supply and fueling infrastructure. From today’s perspective, the DME fuel is more likely to be used in certain niche applications, rather than provide a wide-scale alternative to liquid diesel fuels.

Lately I've been looking into renewable diesel. So far it looks good.


Volvo, Oberon, Safeway and others are using DME. Soon UPS could use DME instead of LNG. Just because you thought it over and don't like it does not mean the world agrees with you.


DME is kind of between LNG and diesel. The fuel is much easier to transfer and store than Cryogenic LNG. Its very similar to propane as a liquid at room temperature but pressure slightly above atmospheric. It is a compression ignition fuel so it can operate at diesel like efficiency because it doesn't have lower compression and Knock issues like natural gas. Its oxygenated leading to the lower PM emissions, but will still have some knock issues due to mixing controlled combustion. The very low viscosity make the direct injection system a bit of a challenge, but because its oxygenated, it doesn't need the very high pressures that diesel does for low PM emissions, likely 4,000psi instead of 35,000psi. But the infrastructure challenge will likely limit it to niche markets at first. One thing I'm betting is that it won't become a locomotive or marine fuel because like propane is is heavier than air when it leaks so safety is an issue that is hard to overcome at the larger onboard volume in those applications.

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