Daimler set to launch DI CNG in cars?

Bosch and Daimler are working on a joint programme to introduce direct injection (DI) CNG engines in passenger cars. Development work on the new compressed natural gas (CNG) engines is set to be completed in 2017 after which "Bosch and Daimler will decide on market start", according to well-placed sources.

Development work, which began in the first quarter of 2015, is centred around several dedicated research engines, including single-cylinder engines.

But, according to sources, "the technology will be tested with car engines made by Daimler."

The purpose of the work is to create an engine with improved torque at lower engine speed which will lead to "a more fun-to-drive CNG car".

                                Europe and North America

Both Bosch and Daimler see Europe and North America as the most likely markets "because of infrastructure and availability of CNG".

"But the technology might also be interesting in other regions of the world," noted an insider familiar with the DI CNG programme.

In the context of what prompted the idea for a DI CNG engine, the insider added: "We wanted to improve the driving experience of CNG vehicles, especially when it comes to torque and acceleration, because we believe this will make CNG cars far more interesting for car buyers. They will not only be a rational choice, but might also become an emotional choice too. And if we wouldn't see a business opportunity we would not develop it."

At this stage of development, insiders are not prepared to disclose injection pressures, nor the configuration of the injection technology – common rail with standard injectors or common rail with either piezo injectors or unit injectors.

According to Bosch, direct injection is not only something for diesel and gasoline engines. In compressed natural gas (CNG) engines, it could also make cars even more economical and eco-friendly.

Compared with present systems that use manifold gas injection, Bosch claims GDI could deliver as much as 60 per cent more torque at low engine speed, and offer the prospect of an even more dynamic driving experience in the CNG cars of the future.

Bosch claims there is still no technology for directly injecting natural gas into the combustion chamber. In the Direct4Gas project, researchers are developing a direct injection system for monovalent engines, or engines that run exclusively on CNG.

Complying with standards

Bosch there are good reasons for choosing a CNG engine. The compressed natural gas used in passenger cars is “inexpensive, and emissions from the vehicles (and thus also vehicle tax in many countries) are low”.

But it sees this alternative fuel as offering much greater potential: CNG is mainly composed of methane, whose chemical composition means that cars powered by natural gas could emit far less CO₂ than at present.

In combination with modifications to the engine, the saving could be as much as 33 per cent over a comparable gasoline-powered car.

However, this all depends on combustion processes that are tailored precisely to natural gas.

By 2020, newly registered vehicles in the EU will not be permitted to emit more than 95 grams of CO₂ per kilometer on average. By 2025, this limit could be even lower.

Bosch sees efficient CNG vehicles as being able to help meet exacting emissions standards, and this not only because they emit less CO₂.

“Emissions of particulate matter are also significantly lower than from gasoline or diesel engines,” claims Bosch.

GDI points the way forward

Today's CNG vehicles are generally bivalent, running on gasoline and CNG with engines designed for gasoline direct injection. For CNG operation, they are fitted with an additional manifold injection system for methane.

“The problem with this configuration is that neither the combustion process nor the values for efficiency and emissions can be optimized. For this to happen, the CNG – like the gasoline – needs to be injected directly into the combustion chamber,” points out Dr. Andreas Birkefeld, Bosch’s project leader.

Because methane behaves differently from gasoline when injected directly, it is important to optimize the combustion process for methane.

Direct4Gas researchers and engineers are working on special direct injectors that satisfy much higher standards than manifold injection valves now used.

The injectors have to be robust, gas-tight, and reliable, and precisely meter CNG. Modifications to the engine will need to be kept to a minimum, so that Daimler and others can continue using the same components as for gasoline engines.

The project team will equip experimental gas engines with the newly developed injector, and test it in the laboratory and in vehicles. Researchers will also examine mixture formation, ignition, and exhaust-gas treatment and develop specific solutions.

The team claims that direct injection will be superior to manifold injection in the low-rpm range that is so important for handling. They also estimate that direct injection will increase the amount of torque that can be delivered by as much as 60 per cent.

“This would make the CNG engines of the future significantly more dynamic,” they add.

Production-readiness

The long-term objective of the consortium of automotive suppliers and automakers is to create the conditions needed for making the technology ready for production, and the project is an important step toward this goal.

The consortium is led by Robert Bosch GmbH. Other partners include Daimler, and the Research Institute of Automotive Engineering and Vehicle Engines Stuttgart (FKFS). Umicore AG & Co. KG is an associated partner.

Following a resolution of the German Bundestag, Direct4Gas is supported with €3.8 million from the Federal Ministry for Economic Affairs and Energy as part of the “Increasing vehicle powertrain efficiency” initiative.