Berlin. Diesel-engine developers are facing a dilemma: To improve the compression-ignition engine's NOx, soot and noise emissions, the main center of heat release has been continually shifted toward less favorable thermodynamic conditions. This results in a higher level of fuel consumption while also increasing CO2 emissions. The challenge to developers is now to meet the stringent requirements placed by the legislator on carbon-dioxide emissions and make the diesel engine more economical without increasing combustion noise or pushing up nitrogen-oxide and soot emissions.
This is where developers see an answer in continuously shaping the rate of injection. Modern injectors, such as the PCR NG injector from Continental, provide the capability of positioning the nozzle needle at any chosen point in the nozzle hole – making it possible to use the effect of constricting the needle seat as a means of timing the rate of injected diesel in virtually any way. Working in collaboration with Continental Automotive GmbH, IAV has examined the potential of continuous rate shaping and presented its findings at the 31st International Vienna Engine Symposium 2010.
Its test set-up comprised a single-cylinder passenger-car engine with a displacement of around 500 cubic centimeters. IAV's MPEC (Modular Prototyping Engine Controller) with an advanced piezo output stage was used for controlling the engine. IAV's universal FI2RE control unit delivered the signal for actuating the injector, with IAV's Injection Analyzer taking care of analyzing the rate of injection.
Using the test set-up, for example, it was possible to replace two conventional pilot injections with a ramp-shaped curve ("continuous rate shaping"). "The main injected fuel quantity is converted in a way that produces the desired even rise in pressure while keeping combustion quiet", explains Oliver Predelli, Vice President of Diesel Engines at IAV. Compared with conventional multiple injection, engine noise was three dB(A) lower, halving the level of sound power.
This effect was able to compensate for acoustic drawbacks by reducing raw emissions inside the engine from Euro 5 to Euro 6 level. Proceeding from a Euro 5 calibration, increasing injection and boost pressure halved nitrogen-oxide emissions while leaving particulate emissions and combustion noise unchanged. This was accompanied by a drop in fuel consumption which also led to lower CO2 emissions. "This is where we are expecting a significant improvement and put the potential saving at about five percent", Predelli says. As the next step, continuous rate shaping will be tried out in a full engine with four or six cylinders. The next few years could well see its introduction at production level.
About IAV GmbH:
Employing over 3,000 members of staff across the globe, IAV (Ingenieur-gesellschaft Auto und Verkehr) is one of the leading providers of engineering services to the automotive industry. The company has been developing innovative concepts and technologies for future vehicle generations for over 25 years. Core competencies include production-ready solutions in all fields of powertrain, electronics and vehicle development. Clients include all of the world's prominent automobile manufacturers and component suppliers. In addition to its development centers in Berlin, Gifhorn and Chemnitz, IAV also operates from other locations in Europe, Asia as well as North and South America.