It’s a fact that rising fuel prices, increasing concern with the environment and ever stricter emission laws heavily influences the design and development of the modern automobile.
It started in the 70's when the surge in crude oil prices started the shift of public preference from gigantic gas-guzzling land yachts (think Ford Thunderbird or Chevy Chevelle) to cheaper but more pragmatic fuel-sipping little “puddle jumpers” led by the new Japanese players like Datsun, Honda, and Toyota.
The quest for better fuel economy continued in the 80's, with domestic and import cars taking design cues from their European brethren, dropping their boxy body designs for sleeker and more aerodynamic aesthetics.
The real game changer came in the 90's as the venerable carburetor bit the dust with the widespread adoption of electronic fuel injection and computerized management system in engines. Smaller and thriftier engines started giving out more power than older engines twice the size and number of cylinders.
Advancements in the name of better fuel economy feverishly continue to this day. We see examples like turbocharging of engines with ever-shrinking displacement as well as variable valve timing approaching ubiquity. And we haven't touched on the topic of hybrids and electrics just yet.
Unfortunately, not all developments for better fuel economy took off as well as the previous examples, however promising they seemed. Today we’ll look into a few of my favorites that left me scratching my head and asking “why are we not seeing more of this technology in newer cars today?”
The Bolt-On Hybrid
Probably the technology that gives the most dramatic improvement in fuel economy is hybridization or the use of an electric motor and battery system, either to augment the internal combustion engine (ICE) or provide the main power while the ICE only backing-up when needed. This marriage provides fuel mileage far exceeding any ICE technology on its own while giving none of the range and recharging limitations of pure electrics.
However, hybrid technology is still an expensive option. Prices may not be as prohibitive as an all-electric but buying hybrid model cars easily cost twice more than their gas-only versions.
If full-on adoption of built-in electrified options are probably a decade down the road in terms of affordability, what are we to do with the cars we already have? One option is hybrid conversion.
The appeal of hybrid conversion is that you retain most of what you love about your old car: the looks, comfort, and its good old reliable gas engine, while greatly improving performance and fuel economy at a fraction of the price of buying a new car.
There are a few options available in the market like DIY conversion kits, futuristic retrofits, and commercial level upgrades. However, these options may prove to require a too involved installation process (at least for the average car owner), may have questionable reliability, too expensive, or compatible only to certain vehicle types.
But going back to our topic of promising car tech that never caught on, let me revisit an early attempt on easy and inexpensive hybridization that I thought was smart but never saw the light of day of mass adoption.
Back in 2011, the Department of Engineering Technology of Middle Tenessee State University introduced to the public a hybrid conversion technology that would fit most vehicle types promising the easiest installation I’ve seen in a hybrid retrofit kit. The "Plug-in Hybrid Conversion Kit" (as it's called) uses a flat electric motor that will fit between the wheel hub and tire rims. Basically, if you know how to change a flat tire, you can also easily slap one of these to your car. It’s powered by a battery pack that you load in the trunk and it operates without having to be electronically connected to the car’s controls.
The school apparently released a few working models and the technology got a lot of internet coverage in 2012. But plans for full production or licensing of the technology went nowhere without much explanation and news of the tech pretty much died down after 2012.
The 5-stroke Engine
Even if you’re just slightly into cars, you’ll know that most internal combustion engines are also called 4-stroke engines. So named because the pistons in the engines do four different kinds of strokes to complete a combustion cycle: intake of air and fuel, compression of the air-fuel mix, ignition and expansion (power stroke), and expulsion of the spent gasses (exhaust). Diesel engines have their own 4 stroke that works very similarly.
Even with the advancements in automotive technology, the internal combustion engine is by and large an inefficient system. Results in studies vary but the amount of energy an engine and translate to forward driving motion is just around 10 to 20%. As much as 60% of the thermodynamic energy is wasted out the exhaust.
The only technology in vehicles that scavenges waste energy from outgoing exhaust are turbochargers and the work they produce go into compression of the air prior to intake (allowing the engine to burn more fuel and produce greater power). Turbos do not directly transfer the energy they recoup to driving the crank. Turbos may allow for the efficient combustion of more fuel per cylinder volume but that’s still more fuel.
One tech developed for the internal combustion engine that greatly extends the usage of expanding gases in the engine is the 5-stroke engine. It runs the same first three stroke of a four-stroke cycle but instead of releasing the still energy-rich gas out the exhaust after the power stroke, the same gas goes into a bigger adjacent low-pressure cylinder, pushing down another piston that cranks the main shaft some more before finally spewing the gas out of the exhaust (which could still be used for turbocharging).
Current developer Ilmor Engineering has developed a working gasoline engine model as far back as 2012. Based on their testing, their 700cc turbocharged 5-stroke model has a peak power 130 bhp @ 7000 rpm, peak torque 166 Nm @ 5000 rpm, and fuel consumption of only 226 g/kWh. To compare, Fiat’s award winning TwinAir engine is a slightly larger two-cylinder at 875cc and also turbocharged. The TwinAir makes a maximum of only 85 bhp and 145 Nm @ 1900 rpm.
Granted that the Twin has the advantage of having its peak performance readily available at lower RPMs, peak performance of the Ilmor 5-stroke engine happens in a rev-range similar to any other 4-stroke gasoline engine but with comparable fuel consumption as the TwinAir. Additionally, the 5-stroke is able to perform well without having other common technical advantages like multi-valve intakes or variable valve timing.
Having an extra expansion cylinder is not new technology. In the past, steam locomotives have compound engines that have secondary and tertiary cylinders that perform the same way. A 5-stroke design is not a complex addition to current engine designs neither does it need a new manufacturing process, so as to why it has not been adopted on any vehicle make is a little beyond me.
On the next installment of this blog, will take a look at a few more seemingly practical advances in car tech that promised to improve fuel economy but are curiously relegated to niche circles or just now regarded as technological curiosities.