Although diesel and petrol-powered cars still dominate in Lithuania, the popularity of more environmentally friendly vehicles—electric and hybrid cars—has been growing rapidly in recent years. Pollution from the transport sector is also being reduced by using renewable fuels, but this does not always yield the expected results: according to VILNIUS TECH researcher Dr. Gabrielius Mejeras, the use of bioethanol in hybrid cars can even increase pollution.
 

The Popularity of Hybrid Cars is Growing

The number of plug-in hybrid cars in Lithuania has jumped more than 17-fold over the past five years. According to "Regitra" data, there were 20,307 such cars registered in the country in December 2023, whereas in 2020 their number was just 1,172. While they are still outnumbered by electric vehicles, the demand for hybrid cars is growing very strongly, and it seems this trend will continue.

"As much as people would like to switch to electric cars, the reality is that hybrid cars are currently better suited for driving in Lithuania and pose fewer problems. There are a great many of them in the major cities because they are chosen by ride-sharing service providers. Hybrid cars are not going away and will remain relevant for the next 20–30 years," shares Dr. G. Mejeras, a research fellow at the VILNIUS TECH Faculty of Transport Engineering (TIF).

Renewable Fuels – Not Always a Clear-Cut Solution

According to the researcher, the ecological situation and dwindling fossil fuel resources are encouraging a move away from petrol and diesel or a reduction in their consumption, replacing them with renewable fuels produced from local resources or by blending them.

"Comparing petrol with bioethanol, the latter has a lower calorific value and is less volatile, so when it enters the engine, it cools it more intensely than petrol. For this reason, the combustion temperature in the engine is lower, and fewer nitrogen oxides are formed before the catalyst. However, due to the cooler exhaust gases, the catalyst itself may not operate efficiently enough, and under certain conditions, the total amount of nitrogen oxides, carbon monoxide, and hydrocarbons after the catalyst can even increase. Overall, considering the entire fuel pathway from raw material to combustion, CO₂ emissions can be reduced by about 50 to 80 percent," the scientist explains.

Furthermore, in hybrid cars, a portion of the driving, especially in the city, is done by the electric drive, and the internal combustion engine is often turned off when stopped. As a result, the exhaust gas after-treatment systems do not have enough time to maintain their operating temperature and cool down. They are most effective at neutralizing pollutants when hot, so frequent engine shutdowns and restarts can have a significant impact on real-world emissions, especially during short trips.

"The biggest challenges arise when using bioethanol in cold weather—the after-treatment systems cool down too much and no longer perform their functions well. As a result, using fuels with bio-additives can release even more pollutants into the environment than using petrol or diesel," Dr. G. Mejeras points out the paradox.

Research – to Determine the Optimal Fuel Mixture

Currently in Europe, including Lithuania, the petrol and bioethanol blends most commonly sold at filling stations contain up to 5% (E5) or up to 10% bioethanol (E10).

To determine the fuel mixture ratio that is least harmful to the environment, Dr. G. Mejeras conducted research and prepared his dissertation, "Investigation of the Energy and Ecological Performance Indicators of a Bioethanol-Powered Spark-Ignition Engine in a Hybrid Vehicle." This is a continuation of his bachelor's and master's degree work.

"For my final thesis at college, I wrote about adapting fuels with bio-additives for old, pre-90s engines with carburetors. During my master's studies, I investigated how hydrogen affects engine performance when using petrol and bioethanol blends, and for my doctorate—how to adapt these alternative and environmentally friendly fuels specifically for hybrid cars," he says.

During his doctoral studies, Dr. G. Mejeras investigated how different blends of petrol and bioethanol affect the spark-ignition (SI) engines in hybrid cars, and what impact this has on the engine's energy and ecological indicators.

He conducted part of the tests in the VILNIUS TECH Transport Engineering laboratories and continued the rest in the Czech Republic, at the Technical University of Liberec, which works closely with the Škoda factory. Without changing the engine's software parameters, the scientist tested how the car "gets along" with fuel blends of different compositions, applying the Worldwide Harmonized Light Vehicles Test Cycle (WLTC). This work is one of the first experimental studies in Lithuania where the WLTC driving cycle has been applied to practical tests.

"During the tests, I increased the bioethanol concentration up to 70% and observed the changes in engine operation. I conducted all the tests at a similar temperature—around +20°C—but even in warm weather, under low-load conditions like slow city driving or standing in traffic jams, the neutralization of pollutants decreased," states Dr. G. Mejeras.

Temperature Changes Must Be Considered

After conducting his research, Dr. G. Mejeras determined that even when using higher concentration bioethanol blends, the hybrid car runs smoothly, but the emissions-reducing systems perform much worse.

"This means that the concentration of the bio-additive cannot be high in all cases, even though the current push is to increase it, regardless of whether it's winter or summer. The proportions of the bio-additive should be chosen based on the season and ambient temperature. In cold weather, emissions-reduction systems often fail to reach the required operating temperature and cool down, which can increase pollution in the city. Of course, bio-additives can be used by blending them with fossil fuels, but it is essential to carefully assess the benefits and potential harm of specific bio-additives, especially with changing ambient temperatures," says the VILNIUS TECH researcher.

He adds that the use of biofuels or fuels with bio-additives in hybrid cars is most effective when driving on the highway or without frequent stops, but it causes problems when driving in the city, where one has to stop frequently at pedestrian crossings, intersections, traffic lights, or wait in long traffic jams.

Recognition for Practical Applicability

Dr. G. Mejeras's dissertation was recently recognized by the Ministry of Transport and Communications as the best doctoral thesis in the field of Transport Engineering. According to him, although the work of his competitors was strong and interesting, the commission singled out his research for its practical applicability.

"My research on the impact of the amount of bio-additives in fuel on ecological parameters in the city and the practical applicability of the conclusions was recognized. It's true that during my doctoral studies, I received comments that the work was too practical and not theoretical enough, but the commission saw this as an advantage," he smiles.

Dr. G. Mejeras does not hide the fact that such recognition is a great encouragement to move forward and achieve more. He currently works as a research fellow at the Department of Automotive Engineering in the VILNIUS TECH Faculty of Transport Engineering and plans to continue his research, perhaps with other bio-additives. The researcher asserts that although the path of a scientist is not easy, it is definitely worth taking. He is very grateful to his doctoral supervisor, Professor Dr. Alfredas Rimkus from the Department of Automotive Engineering, whose support was crucial during the dissertation writing period.

"Although you might have to go through great difficulties, everything is doable and achievable. If you did well in your studies, especially your master's, I recommend choosing doctoral studies, as they greatly expand your knowledge. And finally, you get the title of Doctor, which will certainly never hurt," the young scientist encourages.