Modern engines produce more horsepower with more fuel economy but with the same procedure of burning the fuel air mixture and moving the piston, but the old ones and new ones are both four cylinders and do the same thing, so how do they do this and what are the difference berween them??? Do the compression ratio or fuel:air ratio have to do anything with it ?
It's true that modern engines produce more power
The stats tell it all, but here's a quick example in numbers:
1976 BMW M17 1990 cc 113 hp
2011 BMW N20 1997 cc 340 hp
But some things will never change
Air + Fuel = Bang + Emissions
The chemical equation governing internal combustion hasn't changed. This means that the optimum air-to-fuel ratio (AFR) will have stayed the same regardless of the engine.
So how do they do it?
Here are some ways in which more power is eked out of a modern-day engine with the same displacement as an older predecessor:
More ( Air + Fuel ) = More ( Bang + Emissions )
Physics doesn't limit you on how much air and fuel is mixing in a fixed cylinder displacement. As long as the AFR is maintained, adding more air and fuel into the combustion chamber will result in a bigger bang, hence more power.
Over the years, auto manufacturers have achieved this through many means, including:
- Increase intake manifold pressure - free-flowing air intakes, dynamic charging, ram-air intakes, turbocharging, supercharging, etc.
- Improve volumetric efficiency - variable valve timing, more valves per cylinder
Higher compression ratio
More squeezed air-fuel mixture = more bang, because that's what thermodynamics dictates¹
Manufacturers have been able to bump up compression numbers over the years from typical (for petrol) 9.0:1 ratios to 11.0:1 (13.0:1 in some cases) through various techniques, including:
Moving to an interference-engine philosophy where the valves and pistons occupy the same physical space at different times
Astute piston crown design that "fills" spaces with material where it's not so advantageous to have combustion gases
Use of Direct Injection in gasoline engines
Better air-fuel mixture control
Fuel injection allows much finer control over the air-fuel ratios than what would previously have been possible with carburettors, though the big plus here is lesser emissions than higher power.
In the case of petrol engines, gasoline direct injection takes it to the next level by homogenizing the air-fuel mixture better to squeeze out even more efficiency.
Many things have changed in the engine design landscape. Engineers now have access to:
- better materials - this allows them to push design limits
- better manufacturing capabilities - tighter tolerances, more intricate designs
- better modeling abilities - which allows them to better optimize designs
- better understanding of engine theory/design - every generation of engineers builds upon the work of those who came before them
¹ - it's got to do with the area under the H-S diagram, applicable for any thermodynamic cycle (Otto & Diesel included, of course)
According to me there are 3 major events or advancements which have contributed for most of the efficiency and improvement of the modern engines.
1. Electronic Fuel Injection
The elimination of the carburettor meant that the Air Fuel Mixture ratio can now be adjusted to a higher degree and an optimum and combustion environment is possible for the engine ultimately improving 3 major factors:
- Better Power output.
- Better fuel economy.
- Better Emissions.
Introduction of an ECU was also a stepping stone for much more digital involvement within the motor vehicle ecosystem.(More on that below)
2. Forced induction(Turbochargers)
Forced induction especially by turbo charging the engine was another milestone which was pioneered with the modern engine paved way for numerous advantage over a naturally aspirated engine. Though the turbo was present since the 50s it wasn't until the late 90s and more recently that the turbo has made its way into most everyday production cars. There are innumerable advantages of having a car with forced induction(especially a turbocharger).
- High performance by comparatively smaller capacity engine.
Instead of having a big block N/A engine, the modern engine sizes have drastically reduced with the latest Ford Ecoboost engine producing around 125 hp of power from a 1 litre engine. This reduce in size itself has many benefits like better fuel economy with no compromise in power, weight reduction of the engine, less C02 output.
- Less specific fuel consumption.
Basically when you are not using the boost from the turbo your car is a measly 1.0 liter ford returning good fuel economy but you are not compromising on power.The best of both worlds.
- Better emissions.
Improving upon the above point, turbos work on the exhaust gases which are usually wasted in a naturally aspirated engine thus its providing more power without producing more C02 for example A 3.5 liter N/A engine producing 400hp will produce higher amounts of C02 than a 2.0 liter turbocharged engine producing 400hp when both are at idle.
Now a days you also get VGT or variable geometry turbo which morphs according to the user needs.
3. Digitization of the engine
This is one of the most important milestone achieved with the modern engine thanks to the computer and the semiconductor industry.
Most of the components of the modern engine are governed by at least one on board computer.This automation allows to achieve unprecedented efficiency compared to mechanical and analogue operation. The below are the important parts which are weaved into the digital environment.
- Right from the Air intake , we have the MAF sensor which senses the amount of air coming into the engine giving that parameter to the ECU to calculate the amount of fuel needed for optimum combustion.
- Variable Valve timing: This technology changed the way valves were operating , the entire combustion process or the otto cycle was optimised thanks to this milestone.
- As Zaid states, Direct injection which allows even more control of the Air fuel mixture coming into the cylinder.
- The Lambda or O2 sensor which measures the proportion of Oxygen in the exhaust gases telling how the previous steps performed and tweaking the next combustion cycle.
There are tons of other computer aids working on the modern engine making it much better than older ones.
Other points which need mention:
- Use of better materials for engine construction.
- Faster introduction of new technology into today's cars unlike the olden days where it used to take years of testing before making into production.
- Better Testing and diagnostics tools and options available to the user.(again computers)
Note: I am aware that most of the above mentioned points were invented a long time ago but it was the recent times they became practical and had an actual advantage on the modern engine design.