'There seems to be a virtually unlimited supply of biofuel feedstock': your letters to Professional Engineering

National effort needed to source biofuel

With reference to Tom Austin-Morgan's comprehensive summary of the options for decarbonising aviation, I believe he was somewhat too pessimistic on one small point. That is that the supply of potential feedstock for biofuel production is limited. 

If any waste organic material can be considered as potential feedstock, there would seem to be a virtually unlimited supply. The problem is collecting it. Perhaps a national collection scheme run in parallel with current recycling systems could be arranged. 

If every available source of organic waste, from agriculture, forestry, domestic, fishing, food processing and even sewage were included, with suitable financial incentives, I suggest that more than enough for both aviation and road transport could be collected. The only limitations would then be the supply of renewable and nuclear electricity and the finance to design and build the manufacturing plant.

Its use in both existing and new aircraft would accelerate progress to net zero compared with all the other new-design-only alternatives, which are unlikely to make a significant impact as a proportion of the total aircraft fleet until the 2040s. 

This option would also have the effect of reducing disposal of waste to landfill.

John Hardaker 

Pioneering nuclear design

In your article about nuclear decommissioning, it was stated that the designers of the Dounreay fast reactor did not incorporate a method of draining the sodium/potassium coolant. 

In fact the fill/dump line, which terminates at the base of the reactor in a flattened nozzle, was used in 1967 to drain the coolant so that the primary circuit leak could be repaired, and again in more recent times to finally drain the system as part of the decommissioning programme. This operated on a simple pressure differential.

My memory is a bit sketchy on the prototype fast reactor which followed, but it also had an installed drainage system for the sodium coolant. This was of a more complicated eductor type, I believe because of the greater height of the reactor. This was not used to ultimately drain the system – instead a main pump was installed in place of one of the coolant circulators, and later a smaller pump was installed through the fuel carousel to remove the dregs at the base of the primary tank.

Robin Herrick

Self-charging at a standstill

A couple of months ago I bought a relatively new Toyota Yaris self-charging hybrid in an attempt to get onto the eco trail. Within weeks I discovered that ‘self-charging’ is not entirely accurate!

I quickly experienced several events where the battery did not have enough power to start the car, putting hospital appointments in jeopardy and requiring the dealer’s mechanics to start the car. Whilst I looked for a solution, I bought a jump-starter power pack for peace of mind.

The final advice from the dealer is to connect a trickle charger every time I garage the car. It turns out that I don’t drive far enough to charge the self-charger’s battery, as it is not a priority to charge the battery to have enough charge to restart the car.

Being a mechanical engineer, I thought it would be an easy programme modification to test the state of the battery and give priority to restore that battery first, but no.

So effectively I have a self-charging hybrid which does not charge itself. Am I alone in thinking the model needs a name change?

Brian Burgess