Unproblematic use of synfuels in classic car engines

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A 1971 Chrysler Valiant served as one of the test vehicles. Photo: Emanuel Freud
A 1971 Chrysler Valiant served as one of the test vehicles. Photo: Emanuel Freudiger
AMAG Classic and Empa have jointly conducted a detailed and scientifically sound investigation into the compatibility of synthetic gasoline in classic cars. Engine components were tested for over a year and driving tests were carried out with selected classic cars. The result: classic cars can also be operated in a climate-friendly manner in the future, as synthetic gasoline can be used in older engines without hesitation.

The AMAG Group has the ambition to achieve a climate-neutral footprint by 2040 and supports Swiss companies that develop technologies or business models for the decarbonization of mobility with a climate fund. For this reason, the AMAG Group has held a stake in the Swiss company Synhelion for several years. This company has developed a technology to produce solar fuels using solar heat. Synhelion will be commissioning its first industrial-scale production plant this year. Helmut Ruhl, CEO of the AMAG Group, explains: "The drive system of the future in the passenger car sector will largely be battery-powered electric vehicles. However, the combustion engine will continue to play an important role in Swiss mobility for many years to come, and not just in classic cars. According to a study by Empa, there will still be around two million combustion engines on Swiss roads in 2040. If it were possible to run these on CO2-neutral fuel, CO2 emissions would be almost 10% lower. Synthetic fuels can make a relevant contribution to reducing CO2 emissions worldwide and a company like Synhelion can secure the prosperity of tomorrow in Switzerland with new technologies."

Synthetic fuels (synfuels) are a promising approach to operating vehicles with combustion engines in a renewable and climate-friendly way in the future. According to manufacturers, they can generally be used in modern models without any concerns. But what about compatibility in classic car engines? "Even though there have been isolated reports that a classic car has been operated with synfuels without any problems and the vehicle manufacturers have given their approval for the current model ranges, we were not aware of any well-founded studies that examined the use of synfuels in classic car engines in detail," explains Dino Graf, who is also responsible for the Classic division at AMAG: "It was clear to us that the majority of owners of valuable classic cars would not embark on adventures with unresearched fuel."

The first scientifically based study carried out in Switzerland today answers precisely this question: synfuels can also be used in the engines of classic and vintage cars without any problems whatsoever. This encouraging finding is the result of extensive trials and tests carried out by Empa, the interdisciplinary research institute for materials science and technology of the ETH Domain, in close cooperation with AMAG Classic, supported by Motorex AG.

In the series of tests, which lasted over a year, the aim was to be able to make reliable, scientifically sound statements about how the various components of an engine and upstream components behave when exposed to synthetic gasoline. Fossil 98-octane fuel was used as a reference fuel and a biosynthetic 98-octane gasoline, which is produced from renewable methanol, was used as a comparison fuel - in a VW Golf I with a 1.5-liter 4-cylinder engine (first put on the market in 1978) and in a Chrysler Valiant with a 3.7-liter 6-cylinder engine (first put on the market in 1971).

At the beginning of the test series, selected components between the tank and the engine were directly exposed to the synthetic gasoline in order to investigate surface changes, signs of dissolution, swelling of the material, etc. No physically, haptically or visually detectable changes were found on the components examined during the observed period, so that their contact with the test fuel can be assessed as unproblematic. The components examined included various seals, carburetors, fuel sensors, fuel hoses and plastic parts such as carburetor floats, fuel filters and fuel caps. At the end of the observation period, there were also no signs of corrosion or other visible changes to the inner walls of the petrol tank, which is usually made of sheet steel as in classic vehicles.

Hardly measurable difference in exhaust behavior with slight advantage of synfuels

The exhaust gas behavior was examined on a VW Jetta, which is considerably more modern than the classic cars, but also significantly more stable in terms of emissions. The regulated exhaust emissions and fuel consumption were determined in three consecutive WLTP (Worldwide Harmonized Light Duty Test Procedure) exhaust measurements for each fuel. The exhaust emissions with bio-synthetic petrol do not differ from those with the fossil reference fuel. In the case of particulate emissions, the simulated highway driving with synfuel shows a slight trend towards lower emissions. Finally, the results with both fuels show no measurable differences in volumetric gasoline consumption or energy consumption.

The VW Golf was used for the wheel performance measurement on a single-axle roller dynamometer at Empa. The vehicle was subjected to a static and a dynamic performance measurement on the chassis dynamometer with both fuels. With both fuels, the Golf achieved approximately the same static wheel performance, and the dynamic wheel performance measurement also revealed no differences between the two fuels.

Extensive test drives were carried out with the two veteran Chrysler Valiant and VW Golf vehicles. Behind the wheel were AMAG Classic employees who know the test vehicles well and were therefore able to correctly classify any subjective driving impressions in comparison with the fossil reference fuel. The VW Golf covered a total of 3369 km and the Chrysler Valiant 2862 km on bio-synthetic gasoline. In both cases, the journeys consisted of mixed operation with up to 150 km of highway driving, short distances of 500 m to 15 km and also longer idle times, as is usual for classic cars.

The Chrysler Valiant was also driven in the Alps, for example in the Engadin and over the Flela Pass. There were no noticeable differences compared to operation with fossil gasoline; the only difference was the slightly different smell of the exhaust gases in both vehicles, which was not perceived as disturbing. The carbon monoxide (CO) measurements and the inspection of the spark plug pattern also showed no abnormalities.

During and after the test drives, the engine oil was removed and tested in a procedure agreed with the Motorex managers. The Motorex engine oil used, which was developed for use in classic cars, showed the expected decrease in viscosity, which could be classified as uncritical in this context.
Most noticeable in one of the two cars was the increase in the iron and lead content in the engine oil. While this was within the expected range in the VW Golf, the values in the Chrysler Valiant were initially unusually high. For this reason, Empa, together with AMAG Classic, carried out further investigations and additional tests using an additional comparison vehicle with normal gasoline. After these tests, a direct connection with the use of synfuel could be ruled out.

Christian Bach, Head of Empa’s Automotive Powertrain Technologies Lab, said after the test series: "In theory, it was to be expected that classic vehicles with old engines would also work with synfuels. But sometimes practice has one or two surprises in store. Fortunately, there were no surprises here for the most part. We were unable to detect any relevant changes in the components, performance or exhaust emissions. Only the results of the oil tests initially made us a little suspicious. While the slight decrease in viscosity was to be expected for technical reasons, we were initially surprised by the increase in lead and iron content. However, further investigations enabled us to gradually rule out any influence of the biosynthetic petrol on these findings. Due to its molecular structure, biosynthetic gasoline has a slightly higher solubility than fossil gasoline. This solubility can dissolve deposits that have accumulated in the engine over decades of operation with leaded gasoline."

Dino Graf adds: "I hope that this scientific experiment will motivate classic car fans to use Synfuels for their vehicles when they become available in the coming years. We will take delivery of the first quantities of Synhelion solar gasoline this year and use it for our classic cars. Because, as of today, we know that it works!"