Assuming everything else is equal (vehicle size, weight, driving style, tires), how do you make ICE engines be more fuel efficient? I noticed my dad’s 1996 Nissan Pathfinder V6 consumes 13L/100km (mixed driving) while a newer V6 is 9L/100km. Car manufacturers claim their engines are “more fuel efficient”, how do they accomplish that?
In: 85
Mostly down to fuel injection. Cylinder shutdown and just the car being better controlled by the computer due to the massive increase in sensors monitoring all the cars systems. For instance while slowing down the computer senses that the wheel speed and engine speed are dropping. instead of slowly dropping to idle it will cut the fuel supply completely so you actually get that bit for free. Also when the engine is less stressed it will shut down a bank of cylinders and basically run on three cylinders because it takes less energy to keep a car at a set speed than it does to accelerate so it doesn’t need them. There are many other things but it’s basically just more monitoring and better computers can reduce wasted fuel that would have been previously used unnecessarily.
Newer Pathfinder has a 9 speed transmission and direct injection. Those two things alone will make a big difference.
Manufacturers have been throwing a lot of money at getting fuel efficiency as it is much more important to the consumer than say 25 years ago as well as regulations Lots of little tiny incremental changes. For example switching from 5W30 oil to 0W20 gets you a tiny bit of mileage. Do a lot of such changes and it adds up. Down side is there more stringent emissions standards.
That you think that is efficient is laughable.
“The UK’s average new car fuel consumption in 2020 was 52.6 miles-per-gallon (mpg) (5.4 litres per 100 km) for petrol vehicles and 56.1 mpg for diesel vehicles (5.0 litres per 100 km).”
You make things efficient by removing weight, increasing aerodynamics (make things smaller), controlling the engine better (ECU etc.) and having a smaller engine (the Ford Mondeo in the UK is the same car as the Fusion in the US… in the US it *starts* at 2.5L, in the UK the largest you can get is 2.0L and it starts at 1.5L).
Stop burning dinosaurs just to carry around tons of metal that do nothing. It doesn’t even make your cars any safer.
* Better control and delivery of fuel (faster sensors and computers) = less unburnt/wasted fuel going out the exhaust.
* Higher compression = higher tempurature = higher thermal efficiency.
* Higher tolerances in construction = less friction losses.
* More advanced intake and exhaust system design = less “pumping” losses. (air and exhaust move through the engine more freely)
The other commenters say important things, but nobody mentioned engine size size. Your example engines could easily just be different sizes.
Someone.probably said but i didn’t see it. Weight. Newer engines use more aluminium and plastic which are easier to move both forward as part of the car and up and down or around in circles as part of a running engine.
Higher compression = better mileage and power
Better breathing, that is larger valves or valves per cylinder to fully exchange burned exhaust with fresh intake air.
Fewer restrictions is intake manifold and either turbocharging or supercharging brings in a more complete intake charge of air.
Transmission settings along with final drive ratio to allow engine to cruise at maximum power RPM. This may mean less power.
More transmission gears so the engine sits at the maximum power RPM over a wider range of car speeds.
Less weight in the car. Plastic or aluminum used in place of steel. Even mini-spare tire over a full-size spare.
Be aware ‘more fuel efficient’ is a marketing term. Nobody states in comparison to what. Same model care 10 yrs earlier? Other cars in same class? Smaller model than other models?
Ok, so there is a pretty big list of things that go into this. Here is what comes to mind.
**1: Things that let the engine operate in a better speed/rpm range.**
In general you want your engine to be spending most of it’s time at low-mid rpm (say 2000 – 3000) and close to full throttle. Lower RPM = less friction losses, higher throttle = less work spent pulling air past a closed thottle. See this graph for [torque and rpm vs efficiency.](https://www.researchgate.net/publication/316530475/figure/fig4/AS:495842618089478@1495229500689/BSFC-map-of-the-engine-7-BSFC-brake-specific-fuel-consumption-rpm-r-min-Max-maximum.png)
Of course making more power (via higher throttle for example) will use more fuel in total, but for each HP generated you’ll use less fuel.
So, if you make the engine as small as you can, then you will use a higher percentage of maximum torque/throttle at cruising speeds, and you’ll be running the engine in a more efficient area of that load graph. (near the top) As long as you don’t make it so small that you need too many revs to make enough power (too far to the right on the graph)
More gears also help you be able to be in that best efficiency area of the graph more of the time, and CVTs are even better.
Turbos don’t help fuel economy as such, but they DO let you make an engine that is way too small for good acceleration, run it at high load during cruise, and then when you need power you just throw boost at it. (see also downsized things like the 1.0 ecoboost). This only gives good economy if you don’t use the power much though.
**2: Things that extract more energy from the same amount of fuel.**
Higher compression ratios get more energy from the same amount of fuel. Both by squashing the air fuel mixture more (compression ratio) and by expanding it more when it goes bang (expansion ratio)
If you can design a better combustion chamber you can get more complete combustion of the fuel too and by avoiding knock you can run more aggressive ignition timing, which again lets you extract more power from the same fuel by firing the spark at a time that imparts power more effectively to the piston.
Direct injection as well as knock sensing both help get you closer to that knock limit, running higher compression and more aggressive timing.
**3. Things that control Air Fuel Ratio better.**
Fuel injection vs carburettors basically. The better control you have over air fuel ratios, the more you can get the engine to target the most effecient ratios as often as possible.
**4. Valvetrain trickery**
Cam profiles are optimised for different engine operating speeds and loads, so a cam profile that’s best for low load, low RPM cruising, will be bad for power at high load and RPM.
Want the best of both worlds? Variable valve timing (and ideally lift) lets you make the engine happier at every combination of load and RPM.
Remember how the reason to run a smaller engine was that you could use higher throttle more of the time, and reduce pumping losses? We can cheat this with valve timing too, this is how Atkinson cycle works.
Example (the percentages are wrong, but gives you the idea): Lets say for (crude) argument’s sake we need to fill the cylinder 40% to make the power we need to cruise. We could run at 40% throttle, and waste a lot of energy pulling air past a closed throttle. OR… we could run at 80% throttle, fill the cylinder 80%, but then leave the intake valve open during the first bit of compression to push half of the air back out again. We make the same power, but with way more throttle and less pumping losses.
The other win is we can use this to gain more expansion ratio. Expansion ratio raises exactly the same way compression ratio does. Problem is we can’t raise the compression ratio too far without knock. But what if we still want to raise the expansion ratio more?
Just raise the compression to like 15:1, but then to prevent knock we leave the intake valve open during a bit of the compression stroke. This lowers the compression ratio, because it’s pushing air out again instead of compressing. BUT we still get a higher expansion ratio, and get more power from the same air and fuel. Again this is the Atkinson cycle trick.
**5. Things that make the engine easier to turn**
Low friction coatings inside the engine, softer valve springs, thinner oils, electrically driven accessories like water pumps, alternators that only run hard on deceleration (when you already want to slow down)
**6. Things that make it easier to move the car**
Aerodynamics, weight reduction, more efficient gearboxes with less friction losses, more efficient tyres with less rolling resistance. Less power to move car = less fuel used.
The process of extracting energy out of gasoline is more or less perfected. Meaning we know how to stoichiometrically extract as much energy out of a certain volume of gasoline.
Basically modern gas engines is as efficient as it will ever be.
However the process of transferring that extracted energy to the wheels is inefficient and that is where we can improve. There are a lot of moving parts to get that energy to the wheels causing a lot of losses. What we can do is reduce the amount of moving components.
The other thing causing new cars to be less efficient in fuel consumption is weight. Cars have gotten bigger and heavier compared to their older counterparts. More mass to move means more fuel is needed.
Going back to what I said about how engines are as efficient as they’ll ever be. It only applies to extracting energy. We can reduce an engine’s fuel consumption by reducing the amount of fuel it needs to burn. Technology like cylinder deactivation reduces the fuel consumption.
3 ways- advancements in technology, lighter vehicles and aerodynamics
Technology regarding fuel injection means the engine can be more efficient. Direct injection lets you inject fuel directly into the combustion chamber (hence the name, right?), and this results in a more complete burn and the ability to fine tune exactly how much fuel goes into the cylinder. The more complete combustion means there’s less wasted energy in the form of heat, so a higher compression ratio can be used, which will deliver a little more power and (usually) a small bump in fuel efficiency. Direct injection is often paired with turbocharging, and having a turbocharger lets manufacturers use a smaller engine but produce the same, or often more, power. Smaller engine running low or no boost means more fuel efficiency. Variable valve timing is a common way to increase fuel economy and power- by being able to hold valves open longer, and control their overlap, but if you’re holding them open longer you’re drawing in more air and increasing efficiency. Cylinder deactivation is exactly what it sounds like- at a steady speed with no load or minimal load, the engine will shut down one/multiple cylinders. That v8 just dropped 4 cylinders, and now is running on just 4. Less fuel is used, mpgs are increased
Vehicles are being made lighter and lighter- either from lighter metals like aluminum, plastic bumper covers, or just less material (your frame is a good example of this). Dropping 5-10 pounds here or there adds up, and when everything is combined the effect can be dramatic. A god example of this is ford switching to high strength steel and aluminum for the 2015 f150, and making the supercrew trucks about *700 pounds* lighter than the same supercrew truck was in 2014.
Aerodynamics will, of course, play a part as well. Having o push a vehicle through the air takes effort, which requires power, which needs fuel. Little things can add up here as well- you’ll notice most modern vehicles have air lips/dams on the front, some even have motorized ones. The less air that goes under the vehicle, the less drag it has underneath. Panels are made to redirect air more efficiently, even the rear of trucks are designed to create a low pressure zone behind them, you can see this with little lips, almost like a small built in spoiler, built into the tailgate design. Ford has slots above the front bumper to redirect airflow to the sides instead of having it just smash into the front. Many vehicles now have active grille shutters, which open or close and can effect airflow as well.
Sounds kind of complicated, right? Now combine them all, and is no wonder we can get some decent fuel economy numbers if we drive modern vehicles correctly. This isn’t even including things like stop/start, or gearing, or adding more gears into the transmission. And obviously this isn’t true across the board, but it gives you a little bit of an idea
Internal combustion is pretty much at the limits of what can be realistically achieved in terms of efficiency. ICE has been undergoing non-stop development for over 100 years now. Improvments are tiny at this point, generally centered around better computer control of the combustion and tiny weight savings.
If we want to really make strides in extracting ever more useful quantities of energy per unit of fuel, we need to start combining the engine with other technologies like electric motors. This then enables the ICE to run other more efficient cycles (like the Atkinson cycle) and stay at it’s absolutely peak efficiency RPM for longer.
Anyway, there are things we can do, but It’s really just diminishing returns now.
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