Some of the technology with the biggest impact isn’t new or revolutionary; it’s making old technology work better. Cases in point, researchers at the Technische Universität München (Technical University of Munich, TUM) continually modify and test diesel engines to meet and exceed current (and future) emission standards. I suppose this is the sort of engineering we’d expect from Germany. It might even be considered ‘routine’ work. That would be a gross underestimation. Diesel engines, particularly in trucks and busses, are among the worst polluters in the world. Devising workable (that is to say, commercially feasible) solutions for diesel engines is no small thing.
In a recently announced line of research, the TUM team is close to the goal of bettering the emission levels of the very stringent Euro 6 standard, scheduled for 2014. In testing new engine components, the TUM team has developed a method of capturing air samples within the combustion chambers of a running engine without compromising the efficiency of operation. A small tube is shot into the chamber up to thirteen times during a single compression stroke of the piston, sampling the combustion gasses within a millisecond. This produces an accurate and detailed profile of the gas composition for analysis.
The test engine, a two-ton truck motor dubbed NEMo (a German acronym: Niedrigst Emission LKV DieselMOtor [Lowest Emissions Truck Diesel Motor]) has been run at full load yet produces almost no discernable exhaust smell, and is close to meeting the Euro 6 standard of 5 milligrams of soot and 80 milligrams of nitrogen-oxide per kilometer.
The TUM researchers designed the LVK [truck] test engine in such a way that the air-exhaust mixture is injected into the combustion chamber under high pressure. The engine’s turbo-charger compresses the mixture to ten times atmospheric pressure (measured in bar) – more than double the pressure mass-production vehicle engines can handle. Compressed in this way, the air-exhaust mixture contains enough oxygen for the diesel fuel to burn completely.
They coupled this innovation with another improvement, at the nozzle that injects diesel fuel into the combustion chamber. It atomizes the fuel into microscopic droplets, allowing them to burn completely. In larger droplets produced by conventional injectors, only the outer layer of fuel molecules are burned, like an onion whose first layer has been peeled. The resulting exhaust fumes envelop the fuel droplets, shielding them from the oxygen. The shell of exhaust gases gets increasingly dense with each “onion layer” that goes up in flames. Eventually it becomes practically impossible for oxygen to react with the fuel. The result: soot formation.
The NEMo injector nozzle atomizes diesel fuel at a pressure of over 3000 bar – standard is 1800 bar, at most – to generate a fuel mist that burns very quickly and practically soot-free. Unfortunately, this also results in surging temperatures; a tricky situation, and finding the right balance between the three parameters of exhaust gas recirculation, boost pressure, and nozzle configuration proved challenging indeed.
Using the new combustion chamber sampling technique, the team is working on the details of soot formation at the point of combustion, with hopes to achieve even greater lowering of this major pollutant. It should be emphasized that the NEMo engine is experimental. Turning it, or its improved variants, into a production-line engine is another process altogether. Nevertheless, demonstrating that ‘old’ technology can be made to conform with modern emission standards, may lead to production engine models that are less expensive to produce and service than radically different technology.