Lemnos 11/9/03 Comparison of PM exhaust emissions measured at a chassis dynamometer and on-road chasing on a test track

2. LABORATORY MEASUREMENTS 2a. Legislated Emissions (cycles) Figure A(6) shows the emissions during NEDCs. The data from three cold and five hot cycles were separately averaged. One of the cold cycles gave much lower THC and CO emissions than the other two (CO was close to zero), as can be noticed from the wide range bars. CO during hot cycles was at background levels. Figure B(7) presents the average PM mass emission rates during cold and hot cycles together with the results of the chemical analysis. Sulfate and VOF account for less than 10% of the total PM emissions.

2. LABORATORY MEASUREMENTS 2a. Legislated Emissions (steady states) Figure A(8) shows the emissions in the steady state tests. Total hydrocarbons have not been included because they were always at background level except at 50 km/h, when the emission rate was 0,004 g/km. Also CO at 90 km/h was at background level. Figure B(9) shows the results of the chemical analysis of PM for steady state tests, which yielded significant sulfate levels at 120 km/h and 110 km/h. Obviously, the oxidation catalyst is fully active at 120 and 110 km/h, converting the fuel sulfur to sulfate and oxidizing efficiently the VOF. This is in agreement with the occurrence of nucleation mode particles (see Chapter 4.2.3.2, Figure 15). At 50 and 90 km/h a small amount of VOF was detected, indicating a less efficient oxidation catalyst a this load.

2. LABORATORY MEASUREMENTS 2b. PARTICULATES system Set up The typical experimental setup used in these measurements is shown in Figure A(5). A small portion of the exhaust gas enters the primary diluter (porous diluter) and is diluted with dehumidified (dew point = -10°C as measured in FFA) and filtered air at quasi-constant temperature. Conditions reached with this process are a nominal dilution ratio of 12,5: 1 and a dilution temperature of 32°C. However, at some experiments the temperature or the dilution ratio was varied to check its effect on the particulate measurements. The diluted exhaust gas stream is further divided into 2 branches, called “wet” and “dry” branch by convention. In the heater of the dry branch the diluted sample is heated up to 250°C to evaporate all volatile material, which is subsequently adsorbed in the denuder. The volatile-free sample is then fed to the ELPI. The particles measured at this branch by ELPI are called by convention “solids”. In the wet branch the sample passes through a long tube in order to grow in the counting range of the instruments and the main quantity enters DGI (long residence time, about 3 s). For some measurements the tube was removed (short residence time, about 0,5 s). A small quantity is further diluted (secondary dilution with ejector dilutors) and fed to DDC (Total DR = 180 for cycles and steady state tests or 16000 for speed ramp tests) and SMPS for steady state tests (or CPC for transient tests) (Total DR = 180 or 16000).

2. LABORATORY MEASUREMENTS 2b. PARTICULATES system Set up

2. LABORATORY MEASUREMENTS 2b. PARTICULATES system DGI Total mass and mass size distribution is recorded with the DGI, a cascade mass impactor. The equation that was used for the DGI calculations is the following: DGI PM = Δm DR V(exh) / V(DGI) / Distance where Δm is the net weight on the filter, DR the primary dilution ratio, Vexh the exhaust gas volume of the car, VDGI the volume through DGI and Distance the total distance of the car. Figure A(10&11) compares the total mass measured from DGI at the particulates system following the CVS procedure at steady state tests and for UDC cycles. The percentage difference between the two methods is less than +/-15%. Due to the different sampling conditions (variable dilution ratio at the tunnel, constant dilution ratio at the PARTICULATES system) the mass as given from DGI is about 10 – 25% lower. This should be expected for transient tests. Figure B(12) shows the mass size distribution over UDCs and steady state tests. The peak is at 316 nm (the geometric mean diameter of stages 2 and 3 of DGI) which collects 45 – 50% of the total mass collected on DGI, irrespective of test. It is also evident that about 90% of the mass is less than 1 μm

2. LABORATORY MEASUREMENTS 2b. PARTICULATES system Sensitivity / SMPS Figure A(19) shows the effect of the residence time on the nucleation mode. The scans are taken at 120 km/h during speed ramp tests. Figure B(20) shows the effect of the dilution air temperature on the nucleation mode. The scans are taken at 120 km/h during speed ramp tests on different days.

2. LABORATORY MEASUREMENTS 2b. PARTICULATES system CPC & DC Figure A(25) shows the average number emissions for the cycles. There is no effect of the sampling conditions (32°C or 50°C) for long residence time set up. The cold UDC has higher emissions than the hot. Figure B(27) compares the active surface at different cycles and sampling conditions. There is no effect of the sampling conditions (32°C or 50°C) for long residence time set up. The cold UDC has higher emissions than the cold.

2. LABORATORY MEASUREMENTS 2b. PARTICULATES system ELPI Solid particles are measured with ELPI at the dry branch. Figure A(33) shows the total number emission rate at different speed ramp tests. Dilution temperature does not affect solid emissions, as hot dilution and cold dilution emissions are nearly the same. Moreover, emissions with different residence time (short and long) are also nearly the same.

3. COMPARISONS 3b. Cars 50 km/h 120 km/h The results so far have been from Golf TDI. However, a Ford Focus (1.8l turbo-charged DI) was also measured. Both cars are Euro III certified with oxidation catalyst and used fuels with similar sulphur content (for the Focus reference fuel RF-06-99 with sulphur level of 320 ppm was used). However, they had different nucleation mode B(46), but nearly the same solid particle number emission rate. As can be seen in Figures A(48) and B(49), the maximum of the size distribution is at a lower diameter with the Focus than with the Golf.

2. LABORATORY MEASUREMENTS Comparison PARTICULATES / MATTER Figure A(15) shows the size distributions measured by the SMPS during speed ramp tests. Nucleation mode particles start to appear at 100 km/h. Figure B(37) shows the size distributions measured in a speed ramp test with the MATTER dilutor. A nucleation mode appears at 100 km/h, but only in the second phase, after having driven at higher speed (in the first phase at 100 km/h there is just a small trace of nucleation). The emission rate of nucleation particles changes in the two repetitions at each speed, while the accumulation mode is nearly the same (with the exception of 110 km/h).