Making engines ever-more efficient
Even if turbocharging is the main invention which enables the combustion engine to continue to be competitive, we’ve seen plenty of other innovations alongside.
Constant progress has been made on material quality and design, enabling higher and higher engine speed and pressures, or better specific performance. Injection systems, sparking and combustion layout have also brought a considerable improvement in terms of performance, efficiency and emissions, through faster but better controlled combustion process for Diesel, and knock margin for spark-ignited. High-pressure common rail technology laid the foundations for automotive ultra-high-speed Diesel engines to switch from indirect to direct injection, with efficiencies up to 40% and power density above 100 hp/liter. Medium speed spark-ignited ‘ultra-lean burn’ gas engines are now competing with Diesel units in terms of efficiency, also reaching an incredible 50%.
An increased knowledge in thermodynamics and associated improvements have also contributed to make the engine even better throughout the twentieth century. This is particularly the case with the Miller cycle invented in 1947 in US by Ralph Miller, originally for improving efficiency by extending the expansion stroke, but afterward, combined with high pressure turbocharging to reduce the NOx emissions (something that’s particularly relevant today), thanks to better combustion temperature management. Variable valve lifts and scavenging improvement for large low-speed two-stroke engines are also non neglectable players within the frame of these improvements.
Other avenues were also explored during the 20th century, including the rotary engine from Felix Wankel, presenting certain advantages such as fewer vibrations during operation. This could prove ideal as an electric vehicle range extender, and is also better suited to operation with hydrogen than piston engines.
Chemical engineers from the petrol industry worked tirelessly in parallel to develop gasolines providing higher compression ratios without knocking, and a drastic reduction of particulate matter for Diesel which, for example, reduces the sulfur rate from several percent’s down to several ppm.
Last but not least, in synchronization with the regulation authorities, exhaust after treatment has also been developed, mainly since the 1980’s. This includes the oxidation catalyst, followed by the Diesel particulate filter (after a first trial by Mercedes-Benz in 1985, this system entered in production on the Peugeot 607 in 2000) and at the end, the NOx after-treatment systems, mainly SCR (Selective Catalytic Reduction). Since 1992, automotive Diesel engines NOx and particulate matters are respectively reduced by 90 and 96%.
Internal combustion engines are finally entering the digital era, learning or relearning the need to burn decarbonized fuels like ammonia or hydrogen directly (remember, de Rivaz began with hydrogen in early 1800’s and Lenoir followed in 1860). While internal combustion engines remain the only viable solution for deep sea shipping in the foreseeable future, the world is changing when it comes to smaller powertrains, and shorter-distance marine applications are just one area we’re seeing internal combustion engines joined with intelligent hybrid systems and competing with (or more exactly completing) other upcoming attractive technologies including fuel cells, with their maturity providing a major advantage along with their capability to share the same fuels.
Image credits: Simon Price/Picturepark, Michael Reinhard/Picturepark