Factors influencing the emission

Dans le document Analysis of the cars pollutant emissions as regards driving cycles and kinematic parameters (Page 50-53)

3. Influence of the driving cycles on the emissions

3.2. Factors influencing the emission

Stop frequency (1/km)

Acceleration frequency

(1/km)

Urban 1 15,5 27,3 4,87 7,80

  2 17,3 29,9 4,26 6,61

Rural / sub-urban 1 54,5 3,2 0,24 2,44

  2 51,6 4,7 0,53 2,62

Motorway

/ main roads 1 108,6 0,2 0,01 0,69

  2 114,4 0,0 0,00 0,66

All driving types 1 57,5 11,0 0,56 1,91

  2 52,1 15,2 0,80 2,11

Table 12: Average driving characteristics computed over the 2 respective driving cycles sets for each of the experimentations: 1-WP3141, 2-PNR-Ademe

3.2. Factors influencing the emission

The following analysis intends to analyse and establish the dependency between emissions and driving cycles or driving conditions. However, within our limited data samples, numerous other factors can influence significantly the emissions: the fuel, the emission standard, etc.

In a first step we rank the influence of these different factors, considering all the data. The significant parameters (out of the driving factors) should imply an analysis at a lower level (i.e. if the fuel is a significant parameter, it is necessary to analyse separately Diesel and Petrol data).

We attempt then to identify the necessary level of disaggregation of the sample that would enable analysing the influence of the driving conditions (i.e. the driving cycles or the underlying kinematic parameters).

In that aim, we perform a characterization analysis, in which continuous variable (pollutant emission) is analysed as a function of modalities or qualitative factors (fuel, driving cycles, etc.) and as a function of continuous variables (i.e. kinematic parameters). The statistics relies on a F Fisher test, for variance analysis.

3.2.1. Relative importance of the different factors influencing the emissions

Considering the whole dataset (2 experimentations, all fuels and vehicle categories), a rough analysis identifies the significant factors (i.e. implying a significant variation in the emission) and rank them according to the level of variation induced. These factors can differ for the different pollutants (Table 13).

Three parameters are unavoidable: fuel type (petrol, diesel), the emission standard and the driving condition (driving type, i.e. urban, rural, motorway/main roads and/or driving cycles).

The variability between vehicles (factor: vehicle) is one of the main parameter except for CO2, for which the vehicles parameters and characteristics appear to be less important than the driving type or the driving cycle (which are obviously correlated). This means that the variation of CO2 between petrol and diesel cars and even between the different emission regulations is quite low

Analysis of the cars pollutant emissions as regards driving cycles and kinematic parameters

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46 or insignificant.

The variations induced by the driving conditions can be more significant than the variation induced by the fuel type (HC, CO2) or by the emission standard (NOx, CO2), or even between the vehicles. This highlights well the importance of the driving cycle and more generally of the driving conditions on the emission.

CO (g/km) CO2 (g/km) HC (g/km) NOx (g/km)

The following factors are significant in decreasing order(i.e. their influence on emission is statistically demonstrated)

Vehicle Driving Cycle Vehicle Vehicle

Fuel Type Driving (Urb./Rur/Mway) Emission_Standard Fuel Type

Emission_Standard Vehicle Driving (Urb./Rur/Mway) High/Low motorisation Driving Cycle High/Low motorisation Driving Cycle Driving Cycle

Driving (Urb./Rur./Mway) Emission_Standard Fuel Type Emission_Standard Emitter_Status (Normal/High) Cycle/SubCycle Data set Driving (Urb./Rur/Mway)

Cycle/SubCycle   High/Low motorisation  

 The following factors are not significant (i.e. their influence on emission is not statistically demonstrated) High/Low motorisation Emitter_Status (Normal/High) Cycle/SubCycle

Data set Fuel Type Cycle/SubCycle Emitter_Status (Normal/High)

  Data set Data set

  Emitter_Status (Normal/High)

Table 13: Relative importance of different factors as regards the pollutant emissions It should be also noted that the following factors are generally not significant:

- the Emitter status (except for CO) – This is due to 2 reasons: 1) this status is defined taking into account an over-emission for one given pollutant but is applied for the identified car.

The status applies then also for the other pollutants even if these ones are normal. 2) the number of data concerned is low, then the significance is low.

- The emission data set (except for HC). This demonstrates a certain coherence in the data and then allows the combined analysis of the 2 sets.

- The Cycle/Sub-cycle criteria (which differentiate the emission measured using a whole cycle or using a sub-cycle).

3.2.2. Identification of the possible level of analysis

The previous analysis has demonstrated that further investigations should be conducted while separating the emissions data according to the fuel type, to the emissions standard, and also according to the driving type. However, such a disaggragation should lead to very small sub-samples that should preclude any statistical significance. From Table 10, we can see that the only categories that would enable satisfying analyses are the EURO2 Diesel cars and possibly the Diesel EURO1, the Petrol EURO1 to 3.

The previous analysis was conducted again while separating Petrol and Diesel data. The results are quite similar and identify more systematically the driving conditions as a preponderant emission parameters (Table 14). Roughly, from this table, it appears that Driving Type, Driving Cycle and Vehicle are the preponderant factors for Diesel cars (i.e. the factors of the most significant variation of the emission), while Vehicle and Emission Standard are preponderant for petrol cars.

The Emitter status appears now as almost always significant (except for CO2 and Petrol HC).

The emission standard is also a preponderant parameter except for CO2 Diesel and should

then demonstrate the necessity to analyse the data by vehicle category.

However, when examining which variation is induced by the emission standard, we observe generally an opposition between preEURO, and EURO1 on one side, and EURO2-EURO3 on the other side (Table 15). Depending on the pollutant and fuel, we can observe a clear similarity between EURO2-EURO3 and at least no opposed influence of these categories on the pollutant.

This demonstrates that it is possible to associate these 2 categories for further investigations.

CO (g/km) CO2 (g/km) HC (g/km) NOx (g/km)

The following factors are significant in decreasing order(i.e. their influence on emission is statistically demonstrated) - DIESEL CARS

Vehicle Driving Cycle Vehicle Driving Cycle

Driving Cycle Driving (Urb./Rur./Mway) Driving (Urb./Rur./Mway) Driving (Urb./Rur./Mway) Driving (Urb./Rur./Mway) Vehicle Emission_Standard Vehicle

Emission_Standard Driving Cycle Emission_Standard

Emitter_Status (Normal/High) Data set Emitter_Status (Normal/High)

Cycle/SubCycle High/Low motorisation Cycle/SubCycle

High/Low motorisation Emitter_Status (Normal/High) High/Low motorisation

Data set Data set

- PETROL CARS

Vehicle Driving Cycle Emission_Standard Vehicle

Emission_Standard Driving (Urb./Rur./Mway) Vehicle Emission_Standard High/Low motorisation Vehicle High/Low motorisation High/Low motorisation

Driving Cycle Emission_Standard Driving Cycle Data set

Driving (Urb./Rur./Mway) High/Low motorisation Driving (Urb./Rur./Mway) Driving (Urb./Rur./Mway)

Emitter_Status (Normal/High) Data set Driving Cycle

  Emitter_Status (Normal/High)

Table 14: Relative importance of different factors as regards the Diesel and Petrol pollutant emissions

  CO (g/km) CO2 (g/km) HC (g/km) NOx (g/km)

Influence DIESEL cars  

High emission Urban Urban Urban Urban

  preEURO preEURO Normal Emitter

  High Emitter PNR-Ademe data EURO2

  PNR-Ademe data EURO1  

  High Emitter  

average emission       

  Normal Emitter  

  Rural/Sub. WP3141 data  

  WP3141 data Rural/Sub.

  EURO3 EURO2 High Emitter

  Normal Emitter Motorway/Main road EURO3 EURO1

Low emission Motorway/Main road Rural/Sub. Motorway/Main road Rural/Sub.

  PETROL cars  

High emission EURO1 Urban EURO1 EURO1

  Low motorization High motorization Low motorization PNR-Ademe data

  Motorway/Main road EURO3 Urban Low motorization

  High Emitter PNR-Ademe data Urban

Normal Emitter

average emission       

  High motorization

Normal Emitter Low motorization WP3141 data High Emitter

  Rural/Sub. EURO1 EURO2 Rural/Sub.

  High motorization Motorway/Main road Rural/Sub. EURO3

Low emission EURO3 Rural/Sub. EURO3 WP3141 data

Table 15: Significant categories as regards the Diesel and Petrol pollutant emissions

Analysis of the cars pollutant emissions as regards driving cycles and kinematic parameters

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48

A similar analysis was done as regards the driving type. Indeed, a similarity between 2 driving conditions (i.e. rural and motorway/main roads) should enable the analysis of more consequent data sample. However, this analysis (Table 15) demonstrates that we can conclude to a similarity between rural and motorway driving as regards CO2, HC, but not in the case of CO Petrol and even NOx Diesel, for which emission is low in rural driving but high in urban and in motorway driving (for certain motorway cycles for NOx Diesel).

The above analyses lead us to analyse the emissions by fuel, by driving type. The EURO2 and EURO3 categories will be analysed together enabling to get sufficient data, while the other categories will not be analysed due to the too low number of vehicles.

3.2.3. Influence of the driving type

From (Table 15), we can also conclude that:

- for the Diesel cars, the urban driving leads systematically to higher emissions, while the rural and motorway driving leads to low emissions,

- for the Petrol cars, the urban implies higher CO2, HC and NOx emissions, while CO emission is rather associated with the motorway driving. For these vehicles, the rural driving leads systematically to lower emission.

3.2.4. Influence of the motorisation

In the above tables, we have also observed that the motorisation factor (“High / Low motorisation”) is systematically significant for the petrol cars.

In fact, this factor measures the difference in emissions between 2 car categories (high and low motorisation) but these categories were tested using two different sets of driving cycles. It is then not possible to conclude directly that the motorisation influences the emissions, as the factor implied here is the combination of the motorisation categories and of their respective driving conditions. A specific analysis of these aspects is proposed in Chapter 4.

3.3. Driving cycles and kinematic parameters

Dans le document Analysis of the cars pollutant emissions as regards driving cycles and kinematic parameters (Page 50-53)