Renault is looking into ways to progress its two-stroke two-cylinder diesel engine study so that the prototype powertrain might one day be put into production.
The R&D project, called Powerful, was established with the aim of generating engineering knowledge about two-stroke two-cylinder technology, with the focus being on overcoming upcoming emissions legislation in a cost-effective way for small diesel cars. However, such has been the success of the study that the French car maker is now looking to take things further.
Speaking exclusively to Engine Technology International, Pascal Triboté, innovation project manager in the powertrain research department at Renault, revealed, “We are talking internally as to what to do next. I personally think it’s worth continuing down this path, making some changes to this engine, like making it slightly bigger, like a 1-liter for example, because if we’re going to take this into manufacturing we need volumes, and to get volumes we need more power to cover more market segments.”
Based on findings from the Powerful project, Triboté said that compared to a typical four-cylinder diesel engine, a two-stroke design could realize cost savings of around 30% to meet Euro 6 regs – a crucial development for vehicles placed at the market entry level.
“If you want to manufacture a 2-liter four-stroke diesel for a bigger car that costs perhaps €30,000, you can do that relatively easily and get the fuel economy too. But it’s when you start manufacturing a €10,000 car with a modern diesel engine that meets legislation when issues happen,” explained Triboté. “We have technical solutions to limit the pollutants, but it’s the total cost of the whole system to limit and treat the pollution that’s the problem. We think two-stroke is one way to keep the cost down and have the correct efficiency and emissions level.”
The 730cc two-stroke two-cylinder research diesel is essentially half of Renault’s 1.5dCI base. “As it is a two-stroke, we’re firing each cylinder with the same frequency as the four-cylinder, four-stroke, so in principle we only need half of the cylinder for the same combustion frequency,” explained Triboté. “We took exactly half of this engine – same bore, stroke and design for things like the cylinder block – but what really changed was the cylinder head, gaskets and combustion system. Basically the bottom end of the engine is nearly exactly the same, aside from tribology, which we had to change a little bit to make the two-stroke cycle work.”
Triboté said many of the mechanical parts also had to be adapted on the two-cylinder, as well as packaging a supercharger from Eaton and a turbocharger from CV Turbo, a supplier based in the Czech Republic. Triboté’s team also looked at turbochargers from MHI and Honeywell for this project. The combination of chargers has helped deliver an impressive 70ps power output and 112 to 145Nm torque from 1,500rpm. The engine’s pressure injection system comes from Delphi.
As part of the transformation from 1.5 four-stroke four-cylinder to a 730cc two-stroke two-cylinder, Triboté’s team managed to achieve a weight saving of 40kg for project Powerful, but the prototype’s efficiency gains are not fully known: “We were running late with the project so we didn’t have time to measure CO2. We think, though, at the end of the project we achieved the same CO2 as the four-stroke engine, which was 90g/km,” explained the senior Renault manager.
As for the next stage of the program, Triboté said, “If we are going to produce a two-cylinder diesel, it won’t be this specific engine. It’s an R&D project that’s achieved its goal – to learn enough to go a further step, another closer step to production, but nothing yet has been decided.”