It was Mark Twain who was famously misquoted as saying “reports of my death have been greatly exaggerated”.
With the advent of modern technology, fuel mixtures and electronics, Twain’s remark might be applied to the ICE, its alleged demise being decidedly premature. What’s an ICE exactly? It’s the cool abbreviation for Internal Combustion Engine, quite fitting considering the recent Winter Olympics in Pyeong Chang.
An ICE operates on the ignition of fuel in a combustion chamber. ICEs ingest and then either compress air and introduce fuel into the mix or introduce fuel and compress the air-fuel mixture. The air-fuel mixture is burned, creating energy through heat and pressure which acts upon the moving components of the engine, such as a piston, turbine blade or nozzle. It’s this deceptively simple technology that has assured the longevity of the ICE.
ICE driven aircraft run the gamut from single engine piston aircraft up to full-blown jets. Types of ICE’s include reciprocating and continuous combustion. Reciprocating engines are found in piston-powered aircraft whereas continuous combustion is found in turbojet, turbofan and turboprop configurations. Lesser-used configurations like the Wankel engine use alternative, eccentric rotary design to convert pressure into rotating motion.
With more and more aircraft and engines like the ROTAX 912 iS /and 915 iS filling in the gaps, the development of ICE aircraft doesn’t seem to be slowing either. Recently, Tecnam’s utility workhorse, the P2012 Traveller entered the market as the only piston-twin aircraft of its size. A new addition for a still healthy technology.
ICE operation can be contrasted with that of external-combustion engines (e.g., steam engines), in which the working fluid does not chemically react, rather, the energy gain is achieved through heat transfer to the working fluid through heat exchange.
Early combustion engines didn’t have compression but ran on what available air/fuel mixture could be sucked or blown in during the first part of the intake stroke. It was Leonardo da Vinci that first articulated a compression-less engine in 1509 but it was Alessandro Volta who really got the ball rolling when, in the 1780s, he built a toy electric pistol in which an electric spark exploded a mixture of air and hydrogen, firing a cork from the end of the gun.
In the seventeenth century, English inventor Sir Samuel Morland started using gunpowder to drive water pumps and, in 1794, Robert Street sought to drive an engine with gases obtained when spirits of tar or turpentine were heated. According to an article titled “The Internal-Combustion Engine” in the Naval Engineers Journal, Street’s model had a vertical cylinder with an open end at the top and a closed end at the bottom which was located above a furnace. A small quantity of fuel was poured through a funnel on to the hot plate at the base of the cylinder where it was instantly converted into gas. At the same time, the piston was manually raised by a lever so that air was sucked into the mix with the gas. The mixture was then ignited by means of an outside flame that was held against a touch-hole in the cylinder. The piston was pushed upwards, and its movement was guided by the frame. Streets’ compression-less engine was so revolutionary that it became the principle of operation that dominated for over a century after its invention.
In 1806, Swiss engineer François Isaac de Rivaz built an ICE powered by a mixture of hydrogen and oxygen. Then in 1823 Samuel Brown patented the first compression-less ICE to be applied industrially, equipped to boats and barges. A patent was granted to Englishman William Barnet in 1838 as the first recorded suggestion of in-cylinder compression.
Ten years later, people were beginning to play with the idea of attaching engines to fledgling winged-creations. In 1848, John Stringfellow made a steam engine for a 10-foot wingspan model airplane, marking the first powered flight of an aircraft.
In 1876 Nikolaus Otto, working alongside Gottlieb Daimler and Wilhelm Maybach developed a practical four-stroke cycle engine. The German courts, however, did not hold his patent to cover all in-cylinder compression engines or even the four-stroke cycle, and after this decision in-cylinder compression became universal. Three years later, Karl Benz was granted a patent for his ICE, a two-stroke gas engine, based on Nikolaus Otto’s design of the four-stroke engine. Later Benz designed and built his own four-stroke engine that was used in his automobiles, which became the first automobiles in production.
It’s at this point, in 1903 that mechanic Charlie Taylor built a 12 horsepower, inline engine for the Wright Flyer. From then on, countless inventors poured their expertise and inspiration into building bigger and better engines to get aircraft into the sky faster and for longer. In the following years Léon Levavasseur produced a successful water-cooled V8 engine for aircraft use while René Lorin patented a design for the ramjet engine – a form of jet engine that uses the engine’s forward motion to compress incoming air without a compressor.
Louis Seguin designed the Gnome Omega, the world’s first rotary engine to be produced in quantity and in 1909 a Gnome powered Farman III aircraft won the prize for the greatest non-stop distance flown at the Reims Grande Semaine d’Aviation setting a world record for endurance of 180 kilometres.
Airplanes were used for war starting in 1911, initially for reconnaissance, and then for aerial combat to shoot down enemy reconnaissance aircraft. In 1914 Auguste Rateau decided to speed things up a little, using an exhaust-powered compressor – a turbocharger – to improve performance at higher altitudes, though the project was abandoned after the test results were considered unsatisfactory. The idea was picked up again by Sandford Alexander Moss who built the first successful turbocharger. His efforts resulted in the Armstrong Siddeley Jaguar IV (S), the first series-produced supercharged engine for aircraft use.
Meanwhile, the Idflieg-numbered R.30/16 example of the Imperial German Luftstreitkräfte’s Zeppelin-Staaken R.VI heavy bomber had become the earliest known supercharger-equipped aircraft to fly, with a Mercedes D.II straight-six engine in the central fuselage driving a Brown-Boveri mechanical supercharger for the R.30/16’s four Mercedes D.IVa engines.
In 1931 the Continental A-40, the ancestor of modern opposed engines, was paired with the iconic Taylor Cub and in 1938, Lycoming introduced the O-145, a powerplant which marked the first modern light aircraft engine manufactured in production quantities. This first horizontally-opposed engine would form the basis of generations of Lycoming powerplants for numerous general aviation manufacturers. The world’s first successful helicopter, built and flown by Igor Sikorsky on September 14, 1939, was powered by a four-cylinder 75-horsepower geared version of the O-145, designated the GO-145. By 1943 the Junkers Jumo 004, the world’s first production turbojet engine was also in operational use
The Gloster Meteor, the first turboprop powered aircraft with two Rolls-Royce Trent Engines took to the skies in 1945 and in 1949 the Leduc 101, the world’s first ramjet-powered aircraft took flight. The next year, the Rolls-Royce Conway, the world’s first production turbofan, enters service, powering aircraft like the Handley Page Victor, Vickers VC10, Boeing 707-420 and Douglas DCh-8-40.
In the 60’s the General Electric TF39 high bypass turbofan entered service, delivering greater thrust and much better efficiency. And by the early 70’s Lycoming established the only aerobatic piston engine with FAA certification, powering trainer aircraft for aerobatic and training purposes, Lycoming’s footprint becoming so broad that the chances are highly likely that most pilots have taken to flight powered by a Lycoming Engine at some point in their careers.
Nowadays, the ICE is the driving force behind anything from small piston-powered workhorses like the Cessna 172 to 747’s or turboprops like the TBM Daher 910 and 930, with a cruising speed of a light jet. The remarkable staying power of the ICE is a testament to its relatively simple design and tried and true incarnations over history. But is time running out for the ICE?
Since their inception, electric propulsion has been viewed as the inevitable replacement for the ICE. Even before the Wright Brother’s first flight, when Gaston Tissandier first flew an electrically-powered airship in 1883, questions started arising about the future of the ICE in aviation.
More speculation was stirred up the following year when Charles Renard and Arthur Krebs flew the La France with a more powerful motor. But problems arose early in the piece. Even with the lifting capacity of an airship, the heavy accumulators needed to store the electricity severely limited the speed and range of the aircraft.
Success in a full-sized aeroplane would not be achieved until Nickel-cadmium (NiCad) batteries were developed, having a much higher storage-to-weight ratio than older technologies. In 1973, Fred Militky and Heino Brditschka converted a Brditschka HB-3 motor glider to an electric aircraft, the Militky MB-E1. It flew for just 14 minutes to become the first manned electric aircraft to fly under its own on-board power.
More recently, in 2013, Chip Yates demonstrated that the world’s fastest electric plane, a Long ESA – a modified Rutan Long-EZ, could outperform a gasoline-powered Cessna and other aircraft in a series of trials verified by the Fédération Aéronautique Internationale. The Long ESA was found to be less expensive, have a higher maximum speed, and higher rate of climb, partly due to the ability of the aircraft to maintain performance at altitude as no combustion takes place.
And just last year, Siemens presented a modified Extra EA-300 acrobatic airplane, the 330LE, to set two new world records: on March 23 at the Dinslaken Schwarze Heide airfield in Germany, the aircraft reached a top speed of around 340 km/h over three kilometres and the next day, it became the first glider towing electric aircraft.
Last year one of Europe’s largest airlines, EasyJet, announced that it is looking to begin running services with electric-powered airplanes within the next decade. Collaborating with Wright Electric, the companies want to build aircraft with room for 120 and 220 passengers at a range of 540 kilometres.
The largest hurdle with electric powered aircraft is plain old physics. The energy density of fuel is much higher than the energy density of a battery. While a conventional airplane can travel thousands of kilometres before refuelling, electric airplanes can only travel a fraction of that distance before needing to recharge.
Another problem is refuelling in itself; the scarcity of recharge stations, and the time it takes to recharge make electric propulsion a difficult prospect at this point in time.
On top of all that, batteries are also heavy, and they don’t lose weight as they empty.
Instead, engineers and designers are looking to alter the aircraft and the engine itself, developing working systems that run with better technology, fuel economy, design and aerodynamics.
One of the reasons the ICE has had such an enduring legacy is the innovative technology that the engine is paired with. Better manufacturing materials and quality control have assured lower costs for higher quality ICE configurations. But probably the most exciting development is the arrival of the full-authority digital engine controls (FADEC) system on the GA frontier.
If the ICE is the heartbeat of an aircraft, then the FADEC system is the brains. The FADEC system, is a system that governs all facets of an engine’s performance and propeller management. In a reciprocating engine that uses spark ignition, the FADEC system uses sensors to monitor the status of each individual cylinder as well as measuring the temperature, speed and pressure of the engine. With the information it collects, the FADEC system calculates the ideal fuel injection rate, adjusting the timing of the ignition for best engine performance.
FADEC systems were originally designed for turbine engines in military use. In the 1970s, NASA and Pratt and Whitney went to work combining the first FADEC system with an F-111 coupled with a modified Pratt & Whitney TF30 left engine. The results from the F-111 testing led to the Pratt & Whitney F100 and PW2000 – the first military and civil engines fitted with an FADEC system.
The piston-compatible FADEC technology has been available for over a decade now, with the system becoming increasingly popular in the general aviation market. Both Continental and Lycoming offer FADEC systems for spark ignition reciprocating engines which feature on a wide variety of modern and retro-fitted aircraft.
FADEC systems provide full electronic engine ignition, control of the engines’ fuel injection systems and management functions that monitor all the parameters of an engine’s activity both in flight and on the ground. The system can even control fuel flow without pilot input. This combination of raised efficiency, economics and safety points to even greater leaps in the technology of the ICE.
Two of the main benefits of the FADEC system are improved performance and engine efficiency. Engines with FADEC technology eliminates the need for magnetos, engine priming, carburettor heat or mixture control. In fact, aircraft with FADEC systems only require a single throttle lever up front at the controls. With real-time updates delivered to the pilot constantly throughout the trip, the pilot needs only set the lever to the desired mode. In addition to a more economical and efficient ride, the system improves safety, reducing pilot workload significantly. And it looks like the success of the FADEC will be here to stay, with brand new aircraft like the latest Bell 505 Jet Ranger X featuring a dual channel FADEC system.
FADEC systems aren’t the only contributing factor in the modern durability of the ICE. The versatility of the system to accommodate modern requirements and modifications looks to be extending the life of the ICE into the future. The environmental impact and ever-rising cost of avgas and its future availability has spurred a movement towards alternative fuels.
Aviation gasoline, or avgas, designed for use in ICEs may have to make room for alternative fuel sources that will get more out of an engine at less economic and environmental cost.
Diesel engines aren’t news in the aviation world. German and Japanese airmen have been piloting diesel powered aircraft since the middle of the 20th century, but the weighty block and cylinders of a diesel engine compared to that of a petrol engine caused diesel to fall out of favour. Nevertheless, fresh, highly fuel-efficient diesel engines designed to burn jet-A fuel and alternative fuel technologies are developments that are being keenly monitored in aviation.
In the interim, rising fuel costs and the move towards eliminating leaded fuel had created a push towards diesel fuels that were previously ridden-off by weight and technological limitations. Automotive diesel technology also impacted on the field, with the advent of higher power-to-weight ratios proving much more conducive to diesel fuel sources.
Approved for commercial use in July 2011, biofuels derived from alternative sources are another major area of research in the aviation industry. Currently, aviation greenhouse gas emissions account for two percent of global greenhouse gas emissions and this is projected to rise to three percent in 2050. Scheduled for early this year, Qantas is due to make a trip from Australia to Los Angeles in one of the airline’s brand-new Boeing 787-9 Dreamliners fuelled partly by mustard seeds. And with 72 countries signing up for the UN’s International Civil Aviation Organization’s voluntary program of carbon-neutral air travel growth, it won’t be long before we see more ICE’s with alternative fuel capabilities becoming available on the market.
Of course, to make full use of the efficiency and lower emissions of alternative fuels, an aircraft must be fuel-friendly itself. Ductile composite materials, rather than aluminium, allow for more aerodynamic and sturdy aircraft. Composite materials are also lighter, easing the thirst of aircraft slinking through the air with less resistance. New manufacturing processes have also allowed for the reduction of weight in aircraft components. For example, the ‘monolithic machining’ method adopted by Cessna for the Cessna Longitude features assemblies that are “milled from a single piece of metal rather than assembled from smaller pieces, reducing the number of parts and resulting in more precise tolerances for easier assembly”.
But perhaps one of the most intriguing projects that NASA has been working on is a hybrid-wing body aircraft paired with turbofan engines on top of its back end, flanked by two vertical tails. The futuristic looking aircraft can fly at the same speed as commercial airliners, but it has other benefits too.
On more conventional tube and wing configurations, the engine nacelles mounted under the wings are so large that they generate a large amount of drag. Wing mounted jets are also reaching their limits in terms of size without scraping along the tarmac. NASA’s new design solves both problems with the mounting of the engines on top of the fuselage instead. And in addition to reducing drag and making from for larger, more efficient engines, the hybrid-wing body design also incorporates tail shields that dampen the noise produced by the aircraft.
Incredibly, results from testing by NASA has seen fuel consumption reductions of up to 50 percent, nitrogen oxide emissions reduced by 75 percent, and noise levels drop by 42 decibels when testing high-efficiency engines.
New technological capabilities in terms of computer design and testing has allowed NASA to develop other concepts too. Long but narrow wings and double-wide fuselages both show promise but are yet to be tested in real-life flight conditions. No doubt, these concepts will trickle down into general aviation, saving costs and time in the future.
With the prospect of electric powered aviation emerging into the light, many thought that the long history of the ICE was coming to an end sooner rather than later. But with the advent of innovative technology within the aviation sphere, the ICE endures as the heartbeat of aviation, certain to continue playing a role for a few years yet.