Ask Captain Lim ~ All about Aviation

Warning !

Before you read the letter below,  I must warn you that it is not possible to make Nescafe or Decaffeinated coffee from the exhaust gases of a jet plane. One may think this is possible after reading  this letter.  In theory -  Yes,  in practice - No.
 
If you really need a cup of coffee without the caffeine in it, please go out to the shop or supermarket and buy it, and not take a plane to suck out its exhaust into your traditional Chinese coffee to decaffeinate it.

This is a letter to Captain Lim a senior pilot of a well-known airline. I write to Captain Lim because I love reading his very interesting website. I like exciting professions like being a pilot, but alas! the best I can do about flying  is jump down from a reasonable height and flap my arms as I come crashing down. That’s all the flying I do. I recommend Captain Lim’s  fantastic website.

Dear Captain Lim,

Wow !  you are such an expert on fuel chemistry besides being a pilot. I shall try to check out the octane rating and energy values of kerosene and diesel independently as well. This may require some time as it involves a bit of literature search in fuel and energy technology from an appropriate journal. At the moment I have no idea about the difference except that their energy densities are about the same. Surely, a little common sense will tell any layman like myself that, in the aviation industry, they will look for the lightest fuel with the highest energy values. It is just the question of cost-effectiveness and economics.

Have I lost My Memory ?

No, Captain, I hope not.  I have not made a mistake about that figure on fuel consumption I gave you for a Boeing 707 unless I am beginning to suffer from Alzheimer’s or one of those senile or pre-senile dementia ? Or have I?  You see I know next to nothing about planes, and yet I was able to describe it in terms of “consumption per engine per minutes” in my last letter to you. That shows I actually saw it printed on the brochure in the plane, else how could I use the correct sentence when I have no inkling about jet engines.  If I was unable to recall, or I just made it up, I would have said ‘so many miles per gallon’….for the whole plane for  all the 4 engines like as if I was describing it for a car with 4 pistons / cylinders ? Although it was many, many years ago when I saw it in the brochure at the back of the seat of a plane  in front of me, that figure or some phases printed on it impressed me very much, and I don’t think I will forget that. I cannot remember on which flight it was, on which airline, or where I was going then. Those years I used to travel here and there mainly in the B 707, until in later years I flew in other series of Boeing. When I first saw it, I was comparing it with a car, and wondered the tremendous power and thrust a jet engine must have generated to make it consumed so much fuel ?

Energy Dissipated in Jet Engines

It is either I am loosing memory on that figure (hopefully not), or that the engine technology by now must have improved so tremendously, that engines are currently becoming more and more fuel efficient. I would not be a surprised that with better and better technology,  more effective engines are being developed over the years. Even then, I do admit that the disparity between a B 707 and the current B 777 in terms of fuel consumption as pointed by you is so enormous. What’s more, the load is now almost doubled for the B 777. I do not know what engines were used to power the B 707 in the plane I was in, although I faintly remember they were RR engines.

I faintly remember the name of this engine (Rolls Royce) that   was mentioned in the brochure.  It may not be fair to compare the current powerful Rolls Royce Trent 892 with an older version of the same engine made years ago,  let alone compare it with another type of engine such as Whitney-Pratt. I do not know anything about planes as I said, but I do believe the name of the plane does not mean much. It is the engines, the powerhouse of the plane, whatever the name we like to call it, that matters in terms of power and reliability. The only thing about the body of the plane that matters perhaps is the aerodynamic shape that is going to affect fuel consumption due to air-resistance and drag. Am I not right Captain? But are the B 707 and B 777 aerodynamically the same or about the same between two eras?  But I know through common sense, with a tiny bit of guesswork and logic,  a lot of energy is dissipated and lost by just the need to heat up the extremely cold and huge volumes of air from outside into the intake point of the engines, besides the energy required to compress the air, and to bring up the temperatures to firing / flash points to ignite the fuel inside the turbines, not to say significant energy loss through friction by the blades. That’s not all, a lot of heat would also be wasted in the exhaust. A great deal of energy are lost due to all these factors, and perhaps only a tiny amount are converted into useful work. All these demand a lot of fuel.

The older engines and the aerodynamic shape of the B 707 may not be as efficient as the latest Boeing 777 you are flying. Whatever that is left would be reserved for lifting those tons of load, 336,000 lbs (152.4 metric tons) for B 707 and 632,500 lbs (286.9 metric tons) for B 777 up to 35,000 feet (10.67 km) into the air. It will have to go   against gravity, besides hurtling (the thrust) the plane at near 1000 km per hour against tremendous air resistance, and turbulence from the air flow generated. I believe no matter how aerodynamic the shape, tremendous amount of energy would be required to overcome all these, unless the plane flies higher where the air densities are lower.

But I am unsure if this will affect complete combustion of the fuel since the oxygen concentration is also lower at higher altitudes? You know best on this point. In fact as far as my elementary knowledge of physics is concerned, the more efficient the engines, the more it is going to violate the Second Law of Thermodynamics, and the adiabatic sequence of the Carnot Cycle in an ideal engine. Just as I typed the last sentence, a thought ran up my mind, how does Bernoulli’s Theorem due to various viscosity and air densities, streamlining of air flow and kinetic energy, fit into this fluid dynamics of flight? I am just pondering over this right now. Perhaps I should write a small essay on this later.

The Designer of Reversible Cycles:

Strangely in medicine and physiology, an area and discipline where I am more familiar and conversant than on aviation,  there is also a energy conversion cycle called Kreb’s Cycle, sometimes called citric acid, tricarboxylic acid cycle (after Hans Adolf Kreb, an Oxford  Nobel Laureate) where food (fuel) in its metabolic breakdown  are also similarly converted into energy. But this a slow combustion involving ATP (adenosine triphosphate) and FAD (flavin adenine dinucleotide) metabolic dynamics. In the Kreb’s Cycle, the energy conversion efficiency for a biological machine like our human body, is around 30 % , and this is far more efficient than any jet or propulsion engines or any mechanical machines. No man-made machine of any design, of any kind, whether made yesterday, today or tomorrow, whether for applications in medicine, science or in technology, can be better or more efficient than what is already naturally designed and programmed for us billions of years ago. It was programmed by God, the Designer and Creator Himself.

We can never beat nature, no matter what technological, scientific or medical advances we have frog-leaped over the centuries. Carnot Cycle for an ideal heat engine is Physics, and Kreb’s Cycle is Biochemistry, Medicine and Physiology, but none of these energy utilization systems is as ideal and reversible as the Natural Cycle of Mother Nature – the Energy Balance in the Equations of Ecosystem - the Wind, the Rain, the Sun, and the Water Cycles, the Plants, and the Animals, the Food Chain, the Day and the Night, and the precision circuits of the Earth and other planets round the Sun. These natural and reversible cycles has kept us all alive for a 100 million years on this good planet. It is the Designer’s flawless programme, a retrievable and renewable Cycle for all living things on Earth, and they are not something that could be designed, made or mimic by a physicist or a mechanical / aeronautical engineer, even in their wildest dreams. Let us cherish this Good Earth. Let us be thankful for this life-sustaining Cycles already programmed and given to us. Let’s not break them with our stupid technology. We can never fight Nature.

Now, How to Make Instant Decaffeinated Coffee from Jet Engine Exhaust.

The Super Critical Liquids Poser?

Many thanks for your information that anti-icing agent(s) were added to the aviation fuel to prevent the fuel from freezing at high altitudes where I believe the temperature outside could be down to – 50 0 Celsius or less.   Facts and figures like these  fascinate  me tremendously. I only know that anti-caking agents are added to manufactured food products for similar reasons. But I never thought this problem applies for fuel as well. With this ignorance, I wonder whether they will ever give me a job in the fuel industry ? However, we know that the boiling point of any liquid, including fuels, becomes lower and lower with decreasing gas pressures.

Conversely, the boiling point of liquid increases with increasing pressures. At very low atmospheric pressures volatile fuels like alcohol may just boil off at ordinary room temperatures, but definitely not with kerosene. No fuel except liquid hydrazine and liquid hydrogen I believe, could boil-off even under very low atmospheric pressures. After all, even an air-breathing jet liner can manage only up to 35,000 ft (10.66 km) into the mid to upper region of the troposphere. At that altitude, the temperature is in the region of – 50 to –55 o Celsius, and it should register an atmospheric pressure of only about 260 hPa (26 kilo Pascal), equivalent to 195 mm of Mercury (atmospheric pressure at sea level = 760 mm Hg = 101.325 kPa = 1.01325 bar) from a rough calculation I just made.  The air density 10 km up there is about 0.41 kg / m3 This means at a cruising altitude of 35,000 feet (10,668 metres) the pressure outside, bearing variations in humidity and temperatures, showed it ought to be only (26/101.325) X 100 = 25.66 % compared with that registered at sea level. The approximate calculation is based on a linear-curve table.

Am I right Captain ? It’s an area you can tell me and all of us better. Given this horrendously frigid temperatures – well below the freezing points of most solvents, organic liquids and almost all fuels, no fuel (except liquid hydrogen) could just boil off. They will all be frozen solid hard if not for the anti-icing agents being added, as pointed out by you - thanks to you for this beautiful information I just have just learnt  from you. Even in the intensely frigid environment of outer space, well above the mesosphere and thermosphere, into the exosphere where the condition is near vacuum, exposed fuel could never boil off even at almost zero pressure. All normal liquid fuels will be frozen rock hard at temperatures from – 200o C downwards to almost absolute temperature (near zero Kelvin). But what I wanted to write here is not about the possibility of kerosene getting all iced up, but an extension of a thought of what you said about anti-icing agent being added.

It’s another thought that just ran up my mind a few seconds ago. Suppose in a theoretical situation where we have the intensely high pressures generated within the turbines of a jet-engine acting on the extremely cold air drawn into the engine’s  intake point, we should get a situation where at some point in the compression,  the carbon dioxide from combustion is produced at the right amount, and at the right pressure, and at the right temperature (the hot gases mixed with the very cold air). What happens at that point ? Well to save us all the problem of guessing over this riddle, let me tell you what will happen. The carbon dioxide (CO2) from the exhaust will turn into something called a Supercritical Liqud. Its temperature is neither cold enough to turn the CO2 into solid dry ice, or liquid CO2 (under pressure),  nor is it warm enough to remain perfectly gaseous under normal pressure. It becomes a phase which is “half liquid half gas”. It will achieve this at a certain critical pressure, and at a certain critical temperature.

Technically, we call this a “Supercritical Liquid” When that happens, the gas, especially carbon dioxide becomes a super efficient solvent. This criteria varies from gas to gas. For carbon dioxide it is a very efficient solvent that could dissolve out the caffeine out of coffee at about 45o C at a pressure of 300 atmospheric pressures. It could act as a very clean and non-toxic solvent to extract fats from foods, and also aromatic compounds from herbal extracts  for making perfumes.

In short, if we were to bubble the exhaust gas taken at that particular point in the air compression into our cup of coffee (not practical or possible please – just in theory) it will instantly turn the aroma of traditional and natural coffee into tasteless decaffeinated coffee. The caffeine will simply dissolve out into the carbon dioxide and throw out the caffeine along with the exhaust gases of the air-craft  into the land below to whoever wants it. Isn’t this thought fascinating ? Sounds like a page from Science Fiction doesn’t it?  I am actually asking myself this possibility as a spin off thought of a food scientist (besides being a nutritionist).  My imagination can really run wild in all directions at times. Frankly I am not sure of the answer myself. I am just using scientific logic gleaned from first principles in science and technology to churn and brew up this  cup of strange concoction. Why not ? Why can’t we change our ordinary cup of traditional Chinese coffee into Nescafe if we were pass a tiny, tiny bit of jet exhaust through it at the right pressure and temperature? I know it is very ticklish idea to conjure up. I know everybody will laugh at me at my nonsensical imagination. But I have to affirm to you Captain, this Supercritical Fluid Principle is very real. It is not a science fiction or some non-existing principle I conjure up myself. It is a real technological procedure that has already been applied in the food, pharmaceutical, medical and cosmetic industry. It’s genuine, very real indeed.  If you need to know, that’s how they make Nescafe (decaffeinated coffee) in Germany .

Of course they did not use the exhaust from a jet engine to do this. But the principle still stands, and it is still the same. It is also a procedure being used to extract organic substances such as expensive and rare drugs, herbal medicines, and other high-tech pharmaceutical preparations. In the high tech pharmaceutical industry, we use super-cooled gas at very high pressures to act as a solvent for the isolation of heat-sensitive drugs. This is called Supercritical Liquids Extraction. In food technology, that’s how they make Instant Coffee and Nescafe. It is  also used to purify a substance, such as removing fat or a toxin from food, or to make concentrates of food products. I am combing whatever I know in food engineering, pharmaceutical and drug extraction, in medicine, in applied chemistry, and in  cosmetic manufacturing to boldly tell you this. 

So why not make instant Nescafe from jet exhaust?  So we may have a situation where the air steward(ess) serves hot, natural, aromatic, traditional Chinese coffee inside the cabin, but unwittingly only be able to serve frozen Western decaffeinated coffee outside the cabin made from the exhaust gases of the jet engines. I suppose it serves its purpose for those who refuse to pay air-fare, and be warm and comfortable inside the pressurized cabin.  They may sit outside on the wings to be served another type of coffee ! At a God-forbidden temperature of – 55o C outside, even their tongues and their taste-buds will turn brittle, and instantly crumble into powder even when lightly beaten with a spoon,  let alone feel any taste or pain from intense frostbites They will blown off the wings by a 1,000 km per hour wind, let alone taste any type of coffee ? Just fancy that for imaginary science stories ?  Maybe it is possible in space travels where we can just float about in a vacuum, and drink coffee at leisure.

Maybe I should  write some thoughts about traveling in space later, but right now I have so many other letters to reply. Caution: Just a note of care. It is just not possible to extract even a tiny bit of the combustion gases from the turbines. How are we going to get it out without damaging the blades ? Although it may be possible to divert a little of it through an inlet tube, but how are we going  to maintain  it at 300 atmospheric pressure (30,398 hPa), and kept it at 318 Kelvin (45 o C) exactly in the conditions that is needed to turn carbon dioxide into a Super Critical Liquid even though I believe it  may be generated somewhere inside the turbines? The CO2 will act as a Supercritical Carbon Dioxide Solvent no doubt if we can  pass it through our cup of coffee to remove the caffeine.

I do not know the velocity of the jet blast inside the turbines, but it has to be much faster than the entire plane. The plane itself is already traveling at near 1,000 kph, and the velocity of ejection of the hot gases from the exhaust must be far, far, higher than that, albeit the discharged is divided equally among  all the 4 engines. This is just the principles of physics  and fluid flow mechanics (Bernoulli’s Theorem).  I am only writing this for fun to tease our brains for imagination sake only.  Don’t take me seriously. Theoretically the principle is okay, but in practice – No ! But the extraction of caffeine from natural, traditional coffee to produce decaffeinated coffee, or drugs and natural medicines using the Supercritical Fluid Principles as  I have described IS REAL – VERY REAL INDEED. This part of the story remains valid forever.  The rest are just my wild imagination found only in Science Fiction.

What Rubbish Stuff Am I Writing?

A close friend came  into my room  a short while ago and asked me what was I typing on my computer the whole of this afternoon in  between seeing patients. He reminded me that some of them were still  waiting outside. I told him they can wait.   He remarked that  it looks like I enjoy playing with my computer (sometimes on my violin) more than doing my serious job.  He was very right.  I restrict the appointments to a maximum of only 5 patients a day, so that I can have time for other more enjoyable things.  I told him I was writing to a pilot of a Boeing 777 jetliner telling him how to make instant coffee from the exhaust of his jet engines. He was taken aback,  and remarked that I was a cuckoo.  He asked me why don’t  I write more articles about  health, nutrition, disease,  and medical issues -  something more relevant, practical, and  more interesting to people so that they can benefit from them. Why should I? I have  already written hundreds of articles about health, nutrition, biomedical and other health-related subjects,  and all those sissy stuff.

All these have already  been published here and there, in bulletins, newsletters, company brochures, pamphlets, health magazines, besides notes I write  for my regular public lectures I give almost once a month.   These things are very boring to me by now. A lot of people forget  I am also formally trained in other areas of sciences  - chemistry, zoology, physiology, nutrition, food quality control, and  food engineering too. In fact I have Bachelor and Master’s degrees in them. But I wish could I have just one single Bachelor’s degree, or even a diploma on aviation, aeronautics, astronomy or even on music.  That  would be fantastic, but at last I have not a single qualification in this pet area. How sad, but I am more than willing to exchange all what I have, including exchanging all my current 3 doctorates degrees for a single Bachelor’s degree in astronomy, astronautics, or even on how to pilot a plane.  That would be fantastic. I am  more crazy about physical sciences  than on girlish subjects like biomedical sciences. I landed up on the wrong runaway you can loudly say that. 

If I am an astronaut today, how nice would it be to be able to  see the fantastic stars and galaxies from the depth of space. It will give me inspirations to write outrageous hypothesis on astronomy, cosmic and particle physics, space medicine, space travel,  and space technology, and even on religion  Even writing on music makes  learning more fun, and life less boring. After all, we all need to live a balanced  life which would be far richer,  more holistic, spiritually and materially. Life would be  more fulfilling than merely doing the same old routine job  everyday. Unfortunately, we are all caught up in this commercial world, and have no where to go but eke out a living day-to-day to feed our families. But there  are also  “weird hobbies” I have never had a chance of doing all these years. Making Nescafe from  a  jet engine exhaust is just one. Some say I am mad – perhaps I am.  

Note: Dr JB Lim is the President of the Astronomical Society of Malaysia (ASM)