In the race to chase ever-descending emissions and fuel economy targets, every little bit achieved counts. Mercedes-Benz will launch a petrol V6 engine with a stratified direct fuel injection system, and will make its appearance in an updated model by the end of the year.
Compared to conventional direct fuel injection, which injects fuel during the engine piston’s intake stroke, the stratified fuel injection system allows fuel to be injected during the compression stroke. The company says it allows a much leaner fuel mixture in low load situations, meaning a small gain in fuel economy with “basically no sacrifice in power,” said Bart Herring, Mercedes-Benz USA general manager for product development.
A downside of running very lean fuel mixtures is increased nitrogen oxide (NOx) emissions, a major pollutant. Mercedes’ new stratified fuel injection engines will require special NOx traps as a result, and to that end the company said some of its petrol engines will be equipped with particulate filters from 2017. NOx aside, the new fuel system is said to be very similar to current direct fuel injection systems, with updates limited to software and unique fuel injectors.
Quality of fuel used is a major enabling factor for the propagation of stratified direct fuel injection technology. In the United States, all petrol sold in the country must have a much lower sulfur content than before – from 30 parts per million to 10 parts per million – which is a key factor in the introduction of this more precise fuel injection technique, says Herring.
The aforementioned 10 parts per million sulfur content level is in line with the Euro 5 petrol standard. Meanwhile in Malaysia, Euro 5 petrol will only arrive 2025, and Euro 5 diesel is set to arrive in 2020. The currently available Euro 4 standard RON 97 petrol contains sulfur at 50 parts per million.
