Abstract
Keywords: ETC cycle, emissions, heavy-duty engines, gaseous pollutants, and natural gas engines.
Abstract
The new directive of the European Community 2001/27CE, is an evolution of 99/96 CE and 88/77/EEC, forced by the laws of the State Members in relation to the measures to be taken against the emission of pollutant gases and particles by compressed ignition engines (Diesel) used in industrial vehicles, and the emission of pollutant gases of the Otto cycle engines fed with natural gas or liquefied petroleum gas (LPG) used in vehicles.
The ETC cycle (European Transient Cycle), is a simulation of normal vehicle running conditions with a duration of 1800 s, by means of speed and torque commands (n/T), in different transient conditions of the engine operation; the emissions are sample for the later measure of pollutants emitted during the execution of this conduction cycle.
The Transient Cycle: ETC, was applicable only to the gas engines and to the "advanced" Diesel engines (equip with exhaust gas post-treatment systems). For the normal Diesel engines only an ESC test (13 mode test) and ELC (European Load test) were required.
But after finding certain ECU diesel engines algorithms which were able to recognize the execution of an ESC homologation test, the latest version of the directive (2001/27 CE), foresees the execution of an ETC cycle also to all the Diesel engines (not only the advanced ones) for the approval tests in any of the categories A or B, (although allowing in this case a bigger margin regarding the final emission limits of NOx).
These new requirements of Testing procedures and control systems can not be applied to some test benches based on passive controls , as it would demand the renovation of the emissions measurement systems by means of a full flow tunnel (CVS system) being the costs of renovation of this equipment very high.
In this article the transformations to be done to a typical heavy-duty engine test bench for their adaptation the execution of the ETC transient cycle is described. The original hydraulic brake has been replaced with a c.c.electric machine, capable to brake the engine or make it run in motored conditions.
A new control algorithm is generated to keep the original control strategy of the bench system (n/alpha). This algorithm allows getting the appropriate commands that will permit to obtain a transient cycle fulfilling completely the approaches of statistical validation imposed by the EC directive.
The final pollutants mass flow is calculated from a continuous sampling measurement system from raw exhaust gases during the execution of the ETC test (according to the ISO/DIS 16183), considering the delays of each individual measuring channel. The results obtained with this calculations are compared with the results obtained in the real test measuring pollutants by means of full flow tunnel (CVS system).