Mass flow meter in a hydrogen fuel cell

The balance between reliability and maximum power

Marieke Altena, Hydrogen System Engineer, Green Team Twente

"This year our goal is to make the system reliable, but also to gain on efficiency where possible. The mass flow meter will give us a better insight into the hydrogen consumption of the system and the car during testing."

The battle of the team

It is June 2019 and the Green Team Twente is feverishly making the final adjustments to its vehicle. During the last test - a race in May in Eindhoven - it turned out that the fuel consumption is still too high, the range of the car is 1 litre of fuel is 210km and has to be brought to 900km in a few weeks if they want to have a chance of winning the title at the Shell Eco-Marathon in London on 5 July. Fortunately the problem seems to be relatively easy to solve.

Last year the team faced major challenges during the race: it was 30°C in London and the fuel cells overheated. In addition, the electronics suffered from interference. The finish line was not reached and the disappointment was enormous, because the car was a winner on paper.

WHY THE SHELL ECO-MARATHON?
Of course, the race has to add something to the development work that car manufacturers are already doing. That lies in the search for efficiency. For ordinary cars that is not so important, because hydrogen is a 'green' fuel, so it doesn't matter how much you use it.
But Green Team and the Shell Eco-Marathon take a different view: hydrogen is still far from being produced green. That is why economical driving will remain a point of attention for (many) years to come.
Shell is challenging universities to research extremely fuel-efficient vehicles. Some 100 teams from all over the world take part in 2 classes: Urban Concepts and Prototypes.

URBAN CONCEPTS CLASS
These are cars that have to comply with a number of rules that make them look more like practical usable vehicles. For example, these cars must have four wheels, lighting, indicators and a windscreen wiper.
The rules are changed every year to make the vehicles look more and more like "real" cars. This year, for example, a 2nd door has become compulsory. It is possible that several seats will become compulsory in subsequent years.
Since 2011 the Green Team Twente participates in this class every year and has been active in economical racing since 1978. For the team the choice for this class is logical: the goal of Green Team is to promote hydrogen as a source for the future. The UrbanConcept class is suitable for this because it has more social relevance because the vehicle looks more like current cars.
Other Dutch participants in this class are the TU Delft (also sponsored by Teesing) and the Arnhem Nijmegen University of Applied Sciences (HAN).

PROTOTYPE CLASS
In the class "Prototypes" the limit of pure efficiency is sought and the rules are less strict. The result: a consumption of approximately 5000 km/litre. The TU Delft team participated in this class for many years, but switched to the Urban Concept class in 2020. There are rumours that their team has plans to come out with a vehicle in the Urban Concepts class in 2020.

Flowmeter controls the process

At that time, during development in 2019, the flow of hydrogen could not be read. Grip on the process was necessary to prevent the uncontrolled rise in temperature that fatally affected them.
In fundamental, the reaction process in the fuel cell is faster as the temperature rises, but too hot also results in a loss of efficiency. The optimum is at 70°C.
The solution lies on two sides: measuring and controlling the flow of hydrogen and a better regulated cooling system with a higher capacity.
A flow meter has been chosen, which is being read via Modbus. This allows the team to precisely control the mix of air and hydrogen in the fuel cell. In addition, the team can correlate the data with data from other sensors in the system and thus, for example, optimise engine control.
The fuel cell is also equipped with thermocouples to determine the cooling requirement.
After testing in heat cabinets, the system was tested under race conditions. During a race in Eindhoven in May 3 hours were driven in which the temperature rose to just 70°C at an outside temperature of 25°C. And this without using cooling fans. A proof of concept to be proud of.

Hydrogen fuelcell development

Fuel
25g hydrogen per 250km

Controlloop with zero drift

Top speed
50 km/h

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