In 1801, Richard Trevithick, a Cornish mine manager, built the first steam-powered carriage, considered as the first automobile or motor vehicle. Then in 1834, Thomas Davenport, an American blacksmith, and inventor, developed the first DC electric motor and used it to power locomotives. In subsequent years, Robert Anderson’s battery-powered electric vehicle(non-rechargeable) came up, giving birth to Detroit Electric.
Thereafter came the rechargeable lead-acid battery in 1865 and founded in 1899, Baker Electric became one of the leading automobile manufacturers in America, producing only EVs for nearly two decades. In the same year, a French EV achieved a record range of 290 kilometers per charge. And behold! On 1 May 1899, the EV named La Jamais Contente(‘The Never Satisfied’) achieved the world speed record of 110 kmph. Yes, the EV was the first vehicle to break triple-digit speeds!
So, where was the ICV(Internal Combustion engine Vehicle) when all this was happening? Surprisingly, it was not until 1885 that Karl Benz conceived the first ICV, 50 years after the first EV! And then in 1909, Henry Ford came up with his Model T that transformed the automobile industry. In contrast to the EVs that came at a hefty price, suited to the elites, the Model T came at a much lower price, suited to the masses. This followed the development of many more ICVs on a large scale at cheaper prices. And this is how combustion beat electric, showing that dominance is neither achieved by first-comers nor by technological superiority. Rather, it is they who can successfully break into the mass market who achieve dominance.
Most people have probably come across conflicting views on the problems surrounding the continued use of the ICVs. Sure, oil will run out one day, but won’t we have discovered or created a substitute by that time? And how do we know that the alternatives to the ICV will even work, let alone work better in satisfying current concerns in our quest for a greener future?
The role of an automobile is to convert the stored energy into useful work for the purpose of transporting someone or something from one place to another. The question arises: How much energy? And this leads to the concept of “efficiency”. In the engineering context, this has to do with the discipline of thermodynamics. Not delving deeper into it, the first law tells us that energy can neither be created nor can be destroyed; the amount of energy in a system can only change if it is exchanged with an external system. The second law tells that energy is transformed from one form to another and the amount of useful energy in a system diminishes. What this means is that in the real world, where energy conversions take place now and then, some of the energy involved in a conversion process will eventually become useless heat energy, lost to the surrounding. So how this concept relates itself to the functioning of ICVs and EVs will tell us about their respective efficiencies based on their operating principles.
An ICE basically relies on the process of combustion to convert the chemical energy present in fuels into heat energy to perform work on the engine pistons, ultimately leading to motion. The hydrocarbon chains split apart and react with air in the combustion chamber to form new chemical products and release heat energy. The goal of any engine, thus should be the release of more amount of this heat energy. Now, the single most limitation of the ICE is that it is a “heat engine”. Back to secondary school, Carnot’s Theorem can be used to show that an ideal heat engine powered by petrol would have a maximum energy efficiency of 73%. But while the Carnot Cycle is the basic building block of any heat engine, its underlying thermodynamic processes fail to hold to ICEs. Rather, the Otto Cycle best describes it, which has an ideal efficiency close to 42%(assuming that combustion occurs instantaneously, evenly and the combustion process is adiabatic, which is not so in reality). Thereafter, the ICE comprises of numerous moving metallic parts- transmissions, crankshafts, crankshafts and so on- rubbing and pulling and colliding into each other. So many mechanical losses eventually drop down the overall efficiency to around 15%. Plus, ICEs require periodic maintenance like oil and coolant change, transmission checks, etc.
Coming to the operating principle of EVs, the EM(electric motor) is at its heart. It consists of two fundamental elements- stator(stationary) and rotor(rotating), which work together to convert electric current into kinetic energy. Nikola Tesla’s invention of the alternating current(AC) motor in 1888 paved the way for new innovations in this field. Modern EM is a permanent magnet motor delivering way too high efficiency than an ICE. On the downside, such motors are not cheap since the high energy density permanent magnets are made from expensive rare-earth metals. Whereas an EM’s efficiency can go beyond 90%, an ICEs efficiency dwindles to around 18%.
Driving performance is another area where EVs outweigh their ICV counterparts. Despite the popular misconception, it is not power, but rather torque, that best explains a vehicle’s ability to accelerate. Also, drivers require peak torque at low speeds, like if accelerating from a stop light. As speed increases, torque requirement decreases and once at high speeds, the driver shifts up gears to maintain that speed. Now in an ICV, this calls for multiple gears to match engine speeds with road speeds for a better performance. In contrast, an EM offers peak torque from rest and sustains it up for about 6000 RPM. This means that an EV delivers full accelerating potential for a wider speed range without needing multiple gears, and hence minimizing the mechanical losses as well.
Consider Tesla Roadster which has a maximum speed of 200 kmph at 14000 RPM. The wheel diameter being 63.43 cm, this EV has a gear ratio of 8.28:1 to turn the wheels at their max. speed. With the same gear ratio, an ICV would have inadequate acceleration below 60 kmph(highly inconvenient in urban areas) and would have a max. speed around 120 kmph. All attributes go to the EM which maintains peak torque upto an extended RPM range, whereas the ICE rarely does so. In fact, a given EM can achieve the same accelerating performance than a higher horsepower rated ICE.
Given the advantages of EVs over ICVs in terms of efficiency and driving performance, there is one factor which is the single most obstacle for EVs- Slow recharge rates. While the gas guzzlers can get their tanks filled up in minutes, it takes hours to completely recharge the EV batteries. Technologies like fast charge plug-in and battery swapping have been introduced but are yet to be implemented on a large scale, and these have their own share of problems. Energy storage systems for EVs have improved, from batteries to fuel cells to ultracapacitors and nanotechnology applications. While optimized ultracapacitor storage systems have a greater energy density than ICEs and have the potential to recharge faster, they are yet to be commercialized.
The improvements in energy storage systems for EVs have been commendable. Conventional batteries which come in standardized sizes though have a high specific energy(i.e., amount of energy stored to be made available to propel the car), they have difficulty delivering this energy at a higher rate(i.e., low specific power). Lithium-ion batteries hold the greatest potential for EV applications, though they too have the aforementioned problem. The energy and power capacities of these batteries are co-dependent variables. Plus, the weight of the vehicle is greatly increased due to such battery packs.
Fuel cells(FCs) claim an important role in future transportation technology. A fuel cell is akin to a battery in the sense that it converts chemical energy into electrical energy via electrochemical reactions. But the similarity ends here. While batteries are closed systems that undergo reversible chemical reactions, FCs are open systems whose reactions are irreversible. And this brings about the greatest disadvantage of a fuel cell compared to a battery- Regenerative braking. Besides, FCs use pure hydrogen fuel and the problem is that pure hydrogen isn’t readily available in nature and must be produced. Storage and leakage concerns too pile up the problems.
Consider a Honda Civic(approx. 1200 kg curb weight) cruising along a highway at 120 kmph. It approaches a traffic jam and brakes to a halt. In doing so, it uses up or wastes 0.19 kWh. For comparison, consider Tesla Roadster, which also has a curb weight of 1200 kg. It has a range of 393 km on a single charge of its 53 kWh battery, consuming 0.13 kWh/km. What this indicates is that, during the Honda Civic’s emergency brake, it wasted enough energy to power the Tesla Roadster over 1.5 km! This is where regenerative braking comes into play, saving the huge energy losses.
Owing to such limitations of batteries and FCs, UCs(ultracapacitors) come into the big picture, proving to be the most disruptive solutions. They can deliver high power levels and outweigh batteries and fuel cells as they do not store energy chemically, so the energy-power compromise is not much of a concern. The limitation, though is that due to constraints in the physical space available for UCs, they do not have a great energy capacity as batteries and FCs. But then, nanotechnology applications lead to the development of optimized UCs with much greater energy storage potential. These UCs have both energy as well as power reserves, better than modern batteries and can even replace them as an independent energy source in future. These UCs are rechargeable too, giving the possibility of regenerative braking. For now, they haven’t yet been commercialized. Texas-based UC and battery experts EEStor Inc. claim to have developed an innovative UC.
Battery and UC hybrids too exist, where one overcomes the limitation of the other. Where a battery has great energy reserve, the UC has great power levels. Flash photography has used a similar scheme. While the camera’s battery cannot deliver the peak power required to operate the flash, the capacitor can. However, the capacitor has insignificant energy capacity, so it needs to be recharged by the battery after every flash. This is why we have to wait for a few seconds between clicks when using the flash. In EVs, while the battery can be designed to meet the base load(constant speed) conditions, the UC would meet the fluctuations(acceleration, deceleration, hill-climbing, etc.).
Eventually, since the start of the industrial revolution, we have used everything from sperm whale oil to landfill methane-gas to biofuels to petroleum to make things flare up. Current innovations in EV storage systems are yet to be available at cheaper rates and this is where ICV fuels dominate the market. Nanotechnology is really an intriguing field which has brought about optimized UCs capable of dominating batteries and FCs with recharge rates comparable to ICVs. Potential gains from economies of scale will benefit the introduction of FCs and UCs in the market and hence, engineering focus should be on the development of such technologies for a greener future.