Tuesday, 26 January 2016
Daimler set to launch DI CNG in cars?
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.
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.
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.