Ideas for saving fuel abound. The latest popped up just the other day, when my phone rang. Chris Jennings, who lives on Dublin's northside, was on the line
He wanted to talk about the report on biofuels in Motors of February 12th. Several lengthy phone conversations with Mr Jennings followed, in the course of which he explained that he was an engineer by profession.
He wouldn't give me a phone number for himself, only a fax number which turned out to be that of a newsagent in the Raheny shopping centre in Dublin.
We arranged to meet in Bewleys café on Westmoreland Street, but at the last minute, apparently for family reasons in Germany, he cancelled the appointment. That meeting would have been interesting, as he had offered to show me what he said was some of the considerable documentation on the subject he'd built up over the years.
So, it it's fact or fantasy, nobody can quite tell. From what he told me over the phone - he rang me but I couldn't ring him - it all seemed very intelligent and plausible.
What he was proposing is a system which basically runs on air, reusing the waste heat from a car's exhaust in such a way that a car's thermodynamic profile was changed. This would reduce drag and cut fuel consumption dramatically.
A car would still need petrol, he says, but only in very small quantities. With his system, a car would do 100 mpg, which would indeed be pretty economical.
Mr Jennings points out that cars had been developed which use compressed air. The beauty of this, he claims, is that the car wouldn't need refuelling, apart from the odd drop of petrol. He says he worked on the idea in his workshop - and there is a research company called Airelectric headed by his son, Stephen, who lives in Germany and who has various degrees, including from California.
Mr Jennings says that, while he had approached the various state development agencies here, none had the financial wherewithal - or indeed the interest - to finance a project. It could cost over €1 million for a prototype, but he and his son had interested an Austrian maker of hybrid engines which worked for such companies as BMW and Caterpillar. He hopes that the Austrian firm will investigate the idea thoroughly.
Experts, though, remain less than convinced. "These ideas are more pie in the sky than anything else," says Dr David Timoney of UCD's mechanical engineering department. He couldn't see how such a system would reduce drag: "So many thousands of other people have tried to do the same, making an invention that would cut drastically fuel consumption in a car, and none of them has worked."
People come up with all kinds of strange ideas, he says, and sometimes they look promising on paper - they work beautifully in theory but not in practice.
The energy conversion research centre in UCD, which is linked in with the department of mechanical engineering, has done tests over the years on ideas for saving fuel, but none has worked effectively. Timoney comments that Jennings' idea had an "element of extraordinary improbability about it". He remains deeply sceptical.
Bernard Rice, a research officer with Teagasc in Oak Park in Carlow, is a long-time expert on biofuels. "The exploitation of engine waste heat has been a favoured but not a rewarding subject for inventors over the years," he says.
It can be assumed that makers of engines and cars have given the subject a lot of attention, he says. "If their resources haven't yet yielded a solution, the odds against an individual inventor making the breakthrough must be rather low."
He points out that most vegetable oil conversion kits include a facility to use the waste heat to raise fuel temperature. "This works very well because the increased temperature lowers viscosity and improves atomisation. No similar benefits can be expected from mineral fuels, such as petrol."
So, the many inventors of systems that are supposed to save fuel can only dream on.