What I find interesting is that the larger vehicle manufacturers are still developing the internal combustion engine. Clearly development has been ongoing for decades despite the recent desire of several Governments to ban them – which is something that I feel is shortsighted. I still think that there are a market for this type of power unit with oil or vegetable based fuels.
Many of the manufacturers have been figuring out different ways to find power and/or better fuel economy. Mazda have their SkyActiv engines that use concepts from diesel motors and engineers have been tinkering with internal combustion for well over a century now – right back to Nikolaus Otto, Rudolph Diesel and James Atkinson, all of whom spent years evolving their engines.
Manufacturers have used superchargers, turbochargers, variable valve timing as well as different materials for the block and heads. In most cases, power is increased with a resultant increase in temperature. Heat is effectively lost energy – which is why Kinetic Energy Recovery Systems are so important. They take the heat and convert it back to a usable power source, typically an electric charge.
Thermal Efficiency is the method by which engineers can determine the performance of their engine based on how much heat is wasted. A typical petrol powered engine has a thermal efficiency of about 20-25% which suggests that a lot of the heat from the combustion of the input fuel is lost before being converted to mechanical power – which is the turning of the crankshaft.
Several years ago, Toyota developed an engine that they fitted into the Corolla model which had a thermal efficiency near 40% – and that is similar to a diesel motor. Toyota had combined several existing ideas to create this motor: they used the Atkinson Cycle which can be found in their hybrid motors and they added the variable valve timing to keep the inlet valve open a little longer and this reduced the density of the mix which helped to improve the burn. Those inlet valves were redesigned for more efficiency as well.
Next up, the engine used a compression ratio of 13.5:1 which is very high for a car engine and Toyota added in exhaust gas cooling as well as stop/start technology to improve the economy. Two variants were built: a one litre and a 1.3 litre fitted to the smaller cars in their range. They also went into some Daihatsu models, who collaborated with Toyota (now their parent, having been fully absorbed in the Toyota group two years ago).
Toyota have now expanded the range to a two litre version, called the Dynamic Force! As part of the upsizing of the motor, the engineers have spent time looking at the air flow into the cylinder prior to direct injection squirting in the shot of fuel. This has helped the larger engine deliver a similar thermal efficiency to the smaller ones that have been in production for a while.
In general terms the internal combustion engine is still a poor example of efficiency with too much waste from heat or friction and I suspect that to remove those inefficiencies will need new materials to be developed – or more robust recovery systems to be fitted. Even if an engineer can solve the efficiency problem with the engine, more power is lost through ancillaries still connected to the motor or even through the drivetrain.
The focus is really down to the economy of using such an engine compared to electricity or another source. If the majority of cars go to full electric or hybrid, then the world will use less oil and that could cause the price of a barrel to drop and possibly the price of electricity to rise. If you then add in biofuel or hydrogen powered engines we might actually get a very competitive market! Toyota will clearly be at the forefront of that market.
I have always known of the amount of energy available from ‘the bang’ only a small amount makes it to the back wheels, around 7%-8% for a petrol engine and 11%-14% for diesels, and that most of the difference is in heat, hence the much cooler exhaust of a diesel. These are 70’s figures, undoubtedly have come a distance since then. And not to be confused with thermal efficiency being discussed here, which mechanical and rolling resistance and other titsy loss effects will take a bite out of too.
But the thing is I have only just fitted a PLX gauge (these beauties: https://www.plxdevices.com/PLX-MultiGauges-and-Sensors-s/108.htm) to my car (Subaru sTi engine in a WRX) and now have air-fuel ratio, manifold inlet temp and exhaust temp at the exit of #2 & #4 cylinders. Whilst it is common knowledge (to anyone that looks) how hot cars actually run, it was a bit of an eye-opener to me that just tootling mildly around town the exhaust gas is around 600 – 700 deg C; get stuck into it and hit just over 900 deg C. From what is a tiny little squirt of petrol this heats the air up so much AND gives me a pretty good shove in the hip pocket (just like buying the gauges did, except more fun!).
That is really hot, who’d ‘a thought! And no wonder you see videos of cars with their exhaust manifolds glowing since dark red is around 600 deg C and cherry red is around 900 deg C. Oh, exactly the numbers I quoted. Eeek, it is probably already doing it. For the first little bit anyway…
There is no particular point to this post, just sharing!
The reason I put the gauge on is I had just put new rings in and reconditioned the heads. The tune on the car was done on a dyno when compression was low, so I bumped the fuel pressure up 10 psi as a precaution (turned out to be unnecessary, just sucked up juice faster! so dropped to 5psi up). I put the gauge on as a safety device so I could get the rings run in properly whilst checking for obviously inappropriate air-fuel ratio or high exhaust temps (which indicate likely presence of knocking). 950 deg C is something you don’t want to see to be safe; so far I have not cracked 900 for more than a fleeting moment so all good there!