**6. Testing heavy-duty vehicles**

## **6.1. The route**

**Figure 17.** The NTE test area for the engine of a heavy-duty vehicle.

evaluation is repeated applying lower power output thresholds. The reduction is made with

The coefficient of conformity in operation in terms of exhaust emissions *conformity factor* (CF) is determined in all windows for each analyzed exhaust component as per Eq. (1). In order to render the evaluation in a given averaging interval positive, the determined coefficients cannot be greater than 1.5. The vehicle is considered compliant if 90% of the calculated CF values

*Lj*

The American *United States Environmental Protection Agency* (US EPA) has proposed a test serving the purpose of controlling the exhaust emissions from heavy-duty vehicles under non-test conditions *not-to-exceed* (NTE) that could be applied during the assessment of the actual environmental indexes. The NTE requirements were introduced in 1998 as an ordinance with the consent of the HDV engine manufacturers [25]. The test stringent requirements were gradually extended to other engine categories. As an assumption, the limits and procedures of the test performance were developed as an additional confirmation that exhaust emissions are in conformity with the legislation in the entire range of engine speeds

and loads. The NTE test area of an example engine has been shown in **Figure 17**.

(1)

—admissible emission

1% resolution, maximum 15% Ne max. Lower value renders the results invalid.

where CF—coefficient of conformity in a given averaging window; *Lj*

meet this criterion.

CF <sup>=</sup> *ej* \_\_

116 Improvement Trends for Internal Combustion Engines

of a *j*th component in the WHTC test [mg/(kW h)].

For the tests, the authors selected a road portion of the length of 27 km (**Figure 18**). The road portion well characterizes the operation of vehicles of the GVW exceeding 16,000 kg (long haulage) in the area where the measurements were carried out. The test route started and ended in the industrial zone (point A) where a production facility is located at which approximately 50 heavy-duty vehicles are handled daily. The test road portion can be divided into two parts: a drive on urban roads (portion A–B) and national and regional roads. The drive on national or regional roads depends on the driving direction from/to the entrance to the A2 expressway (Koło) (point D). In the case of driving to the "Koło" expressway entrance, the route went through points B–C and C–D. In the reverse situation, i.e., exiting the expressway and driving to the production facility via bypasses: points D–C and C–B (on the D–C road portion heavy-duty trucks of the GVW in excess of 7000 kg are not permitted.) The above route can be deemed representative of the national transport and logistic infrastructure representing the road infrastructure and the distribution of production facilities in small and medium-sized towns.

**Figure 18.** The measurement road portion used in the on-road emission tests [made based on GPSVisualiser.com].

#### **6.2. Research objects**

For the research, the authors used two heavy-duty trucks (road tractors with semi-trailers) loaded with a cargo of 20,000 and 24,800 kg (**Figure 19**). The first of the objects was fitted with a 309 kW (420 KM) Euro III engine. The other object had a V8 412 kW (560 KM) Euro V engine. Both vehicles were fitted with an automatic transmission (**Table 4**) of the 12+1 configuration. The second vehicle was also fitted with a driver monitoring system. By a continuous analysis of signals from a series of sensors, the system provides real time suggestions, and upon end of trip generates a report on the driving style. The suggestions and the evaluation are presented on a display and have four categories: driving uphill, predicting, braking, and gearshifts. The idea behind the system is to continuously improve the driving skills in terms of fuel consumption and proper use of modern solutions such as: automatic transmission, retarders, or *electronic braking system* (EBS).

**6.3. The exhaust emission correction coefficient**

**Table 4.** Characteristics of vehicles used for the tests.

*Ci* <sup>=</sup> *<sup>e</sup>*

where *Ci*

shown in **Table 5**.

**Table 5.** Values of the emissions limit and *C<sup>i</sup>*

define a dimensionless emission correction coefficient *Ci*

given component in the Euro V standard [g/(kWh)]; *ei*

—correction coefficient of an *i*th component; *ei*

CO 2.10 1.50 0.72 NOx 5.00 2.00 0.40 PM 0.1 0.02 0.20

**Parameter Vehicle A Vehicle B** Displacement 11.7 dm3 15.6 dm3 Number of cylinders/arrangement 6/straight 8/V8

Unit power output index 8.3 kW/t 10.3 kW/t Emission standard Euro III Euro V Exhaust gas aftertreatment N/A SCR

Driver support system N/A SDS Tractor axle configuration 4 × 2 4 × 2 Curb weight including trailer 15,000 kg 15,200 kg Cargo weight 20,000 kg 24,800 kg Type of cargo Big-Bag Steel Type of trailer Canopy Canopy

Maximum power output 309 kW @ 1900 rpm 412 kW @ 1900 rpm

Transmission Automatic 12 + 1 Automatic 12 + 1

Maximum torque 2100 N m @ 1000–1350 rpm 2700 N m @ 1000–1400 rpm

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given component in the Euro III standard [g/(kWh)]. Determined values of *Ci*

coefficient.

**Euro III [g/(kWh)] Euro V [g/(kWh)] Coefficient** *C<sup>i</sup>*

Because the authors could not perform the measurements on two heavy-duty vehicles of the same exhaust emissions standard, the tests were carried out for Euro III and Euro V compliant vehicles. In order to compare the obtained values of the CO emission, the authors decided to

> \_\_\_\_\_ EuroV *e*EuroIII

[25]:

, Euro V—a limit of unit emission of a

, Euro V—a limit of unit emission of a

 **[–]**

(2)

coefficient are

**Figure 19.** Research objects during the on-road emission tests: (a) vehicle A and (b) vehicle B.


**Table 4.** Characteristics of vehicles used for the tests.

#### **6.3. The exhaust emission correction coefficient**

Because the authors could not perform the measurements on two heavy-duty vehicles of the same exhaust emissions standard, the tests were carried out for Euro III and Euro V compliant vehicles. In order to compare the obtained values of the CO emission, the authors decided to define a dimensionless emission correction coefficient *Ci* [25]:

$$\mathbf{C}\_{l} = \frac{\mathbf{c}\_{\text{fireV}}}{\mathbf{c}\_{\text{fireIII}}} \tag{2}$$

where *Ci* —correction coefficient of an *i*th component; *ei* , Euro V—a limit of unit emission of a given component in the Euro V standard [g/(kWh)]; *ei* , Euro V—a limit of unit emission of a given component in the Euro III standard [g/(kWh)]. Determined values of *Ci* coefficient are shown in **Table 5**.


**Table 5.** Values of the emissions limit and *C<sup>i</sup>* coefficient.

**Figure 19.** Research objects during the on-road emission tests: (a) vehicle A and (b) vehicle B.

For the research, the authors used two heavy-duty trucks (road tractors with semi-trailers) loaded with a cargo of 20,000 and 24,800 kg (**Figure 19**). The first of the objects was fitted with a 309 kW (420 KM) Euro III engine. The other object had a V8 412 kW (560 KM) Euro V engine. Both vehicles were fitted with an automatic transmission (**Table 4**) of the 12+1 configuration. The second vehicle was also fitted with a driver monitoring system. By a continuous analysis of signals from a series of sensors, the system provides real time suggestions, and upon end of trip generates a report on the driving style. The suggestions and the evaluation are presented on a display and have four categories: driving uphill, predicting, braking, and gearshifts. The idea behind the system is to continuously improve the driving skills in terms of fuel consumption and proper use of modern solutions such as: automatic transmission, retarders, or *electronic braking system* (EBS).

**Figure 18.** The measurement road portion used in the on-road emission tests [made based on GPSVisualiser.com].

**6.2. Research objects**

118 Improvement Trends for Internal Combustion Engines

#### **6.4. Analysis of the vehicle driving profiles**

In the first, urban part, significant differences in the driving profiles of both vehicles were recorded. Vehicle A had a higher speed than vehicle B (**Figure 20** and **Table 6**). This was caused by higher traffic congestion during the test run of vehicle B. In the rural part, both driving profiles were similar. Vehicle A, during the entire run had a lower average speed (by 5%) than vehicle B. From the analysis of the maximum and average acceleration in the acceleration phase, it results that vehicle B was more dynamic because in both cases its values were higher by 49 and 19%, respectively. The second-by-second emission of CO, NOx , and PM of vehicle A was multiplied by index *Ci* and then compared with the course recorded for vehicle B.

Analyzing the second-by-second emission of NOx

NOx

conditions for the NOx

tive reduction of NOx

(in this method, the on-road emission of CO2

son of the on-road emissions of CO, NOx

**Figure 21.** The tracing of the second-by-second emission of NOx

phase vehicle B had higher values of this emission than vehicle A (**Figure 21**). In the further part of the test, this trend changed and vehicle A had higher emissions. Such a situation was caused by the selective catalytic reduction (SCR) system responsible for the control of the

tion to take place if a 32.5% water solution of urea is applied. Upon stabilization of the engine thermal state, a growth of the exhaust gas temperature takes place; thus, generating proper

version rate of the SCR catalytic converter where the said reactions take place. In standard SCR converters, the highest conversion rate occurs for 250–400°C. Under such conditions, the SCR control system initiates injection of a 32.5% solution of urea into the vehicle exhaust system, from which, following a series of reactions, ammonia is generated and used in the selec-

results that the SCR system had obtained the highest conversion rate after 600 s of the test run, and that vehicle B obtained much lower values of this emission than in the initial phase of the

Next, based on the carbon balance method [30], the gas mileage for both vehicles was determined

been omitted due to relatively low values of the on-road emission of this component by heavyduty trucks remaining within the margin of measurement error. **Figure 22** presents the compari-

obtained lower values and a higher gas mileage. It is noteworthy that it had a significant increase

, CO2

test. In this part of the test, vehicle B also had lower emission of NOx

reduction. The temperature of the exhaust gas also influences the con-

Measurement of Exhaust Emissions under Actual Operating Conditions with the Use of PEMS...

. From the recorded course of the second-by-second emission of NOx

20°C) and under these conditions, the exhaust gas temperature is too low for the NOx

 emission, fitted in the exhaust of vehicle B. In the first phase of the test, the SCR system was most likely inhibited, as the tests for both vehicles were initiated from a cold start (a cold start is to be construed in this case as starting the engine at an ambient temperature of over

, the authors observed that in the first, urban

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121

, it

compared to vehicle A.

, CO, and HC is taken into account). The HC part has

, PM, and the gas mileage. In all cases, vehicle B

for both vehicles obtained during the on-road tests.

**Figure 20.** Speed profiles of the tested vehicles obtained during the on-road tests described with function *V* = *f*(*t*).


**Table 6.** Parameters characterizing the test runs of both vehicles during the on-road tests.

Analyzing the second-by-second emission of NOx , the authors observed that in the first, urban phase vehicle B had higher values of this emission than vehicle A (**Figure 21**). In the further part of the test, this trend changed and vehicle A had higher emissions. Such a situation was caused by the selective catalytic reduction (SCR) system responsible for the control of the NOx emission, fitted in the exhaust of vehicle B. In the first phase of the test, the SCR system was most likely inhibited, as the tests for both vehicles were initiated from a cold start (a cold start is to be construed in this case as starting the engine at an ambient temperature of over 20°C) and under these conditions, the exhaust gas temperature is too low for the NOx reduction to take place if a 32.5% water solution of urea is applied. Upon stabilization of the engine thermal state, a growth of the exhaust gas temperature takes place; thus, generating proper conditions for the NOx reduction. The temperature of the exhaust gas also influences the conversion rate of the SCR catalytic converter where the said reactions take place. In standard SCR converters, the highest conversion rate occurs for 250–400°C. Under such conditions, the SCR control system initiates injection of a 32.5% solution of urea into the vehicle exhaust system, from which, following a series of reactions, ammonia is generated and used in the selective reduction of NOx . From the recorded course of the second-by-second emission of NOx , it results that the SCR system had obtained the highest conversion rate after 600 s of the test run, and that vehicle B obtained much lower values of this emission than in the initial phase of the test. In this part of the test, vehicle B also had lower emission of NOx compared to vehicle A.

**6.4. Analysis of the vehicle driving profiles**

120 Improvement Trends for Internal Combustion Engines

PM of vehicle A was multiplied by index *Ci*

vehicle B.

In the first, urban part, significant differences in the driving profiles of both vehicles were recorded. Vehicle A had a higher speed than vehicle B (**Figure 20** and **Table 6**). This was caused by higher traffic congestion during the test run of vehicle B. In the rural part, both driving profiles were similar. Vehicle A, during the entire run had a lower average speed (by 5%) than vehicle B. From the analysis of the maximum and average acceleration in the acceleration phase, it results that vehicle B was more dynamic because in both cases its values were higher by 49 and 19%, respectively. The second-by-second emission of CO, NOx

**Figure 20.** Speed profiles of the tested vehicles obtained during the on-road tests described with function *V* = *f*(*t*).

**Parameter Unit Vehicle A Vehicle B Percentage ratio vehicle A/**

m/s2 0.21 0.26 80.77

Distance, s km 26.57 26.88 98.84 Maximum speed, Vmax km/h 92.00 84.52 108.14 Average speed, Vave km/h 45.73 48.56 94.17 Minimum acceleration, amin m/s2 −2.93 −2.80 104.64 Maximum acceleration, amax m/s2 1.28 2.53 50.60

**Table 6.** Parameters characterizing the test runs of both vehicles during the on-road tests.

Average acceleration in phase of the ramp-up,

aśr

, and

and then compared with the course recorded for

**vehicle B [%]**

Next, based on the carbon balance method [30], the gas mileage for both vehicles was determined (in this method, the on-road emission of CO2 , CO, and HC is taken into account). The HC part has been omitted due to relatively low values of the on-road emission of this component by heavyduty trucks remaining within the margin of measurement error. **Figure 22** presents the comparison of the on-road emissions of CO, NOx , CO2 , PM, and the gas mileage. In all cases, vehicle B obtained lower values and a higher gas mileage. It is noteworthy that it had a significant increase

**Figure 21.** The tracing of the second-by-second emission of NOx for both vehicles obtained during the on-road tests.

**7. Conclusions**

**Abbreviations**

CAN controller area network CF conformity factor CI compress ignition CNG compressed natural gas CVS constant volume sample DOC diesel oxidation catalyst DPF diesel particulate filter EBS electronic braking system

EEV enhanced environmentally friendly vehicle

IARC International Agency for Research of Cancer

EFM-HS exhaust flow meter high speed EGR exhaust gas recirculation ELR European load response

EPA environment protection agency ESC European stationary cycle ETC European transient cycle

FC fuel consumption

HDV heavy-duty vehicle

LAN local area network LDV light-duty vehicle LPG liquefied petroleum gas

MSS micro soot sensor

FID flame ionization detector GPS global positioning system

The reduction of exhaust emissions requires a continuous search for new solutions in both engine design and methods of engine testing. A main factor stimulating this development is the exhaust emission legislation in which they are in progress. The advancement of exhaust emission measurement techniques provides new possibilities of engine and vehicle testing particularly under actual conditions of operation (RDE). One may suppose that this method will become prevalent and will gain significance. The aim of the legislators and manufacturers should be the acknowledgment of the RDE measurements as one of the main methods of homologation testing works. The aim of introducing such changes should be completed as soon as possible and the enforceability of the implemented legislation should be global.

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**Figure 22.** Comparison of the on-road emission of CO, NOx , CO2 , PM and gas mileage of the tested vehicles.

in the gas mileage (by 2.9 dm3 /100 km). The cost of fuel is currently the main cost of operation of long-haulage trucks. The greatest drop was observed for the on-road emission of NOx , which mainly resulted from the application of the SCR system in vehicle B.

The reduction of exhaust emissions requires a continuous search for new solutions in terms of both the design of engines/powertrains and the methodology of their testing. A factor stimulating this advancement is the exhaust emissions legislation. The advancement of the exhaust emissions measurement technology has created new possibilities in terms of measurements performed under actual conditions of operation. Supposedly, this particular method will be further developed and will gain in importance. A natural reaction of the legislators and manufacturers should be the recognition of measurements under actual operation as one of the main methods of homologation testing. Relevant works aiming at the introduction of such changes should finish without delay and the resultant legislation should be of global outreach.

The PEMS-based measurements have provided invaluable information regarding the emissions under actual operation of vehicles including their operating parameters. One of the most important observations is the difference in the emissions between the homologation tests and the tests performed under actual operation. The results of the measurements performed on LDV vehicles indicate significant differences, particularly in terms of NO<sup>x</sup> and HC. The reasons for that are different parameters in the homologation tests and those under actual operation. The differences for the HDV Euro III and Euro V compliant vehicles are big, particularly in terms of NOx and PM. They amount to 45 and 10%, respectively. However, referring these results to the Euro III (vehicle A) and Euro V (vehicle B) limits, the differences are smaller—the reduction of the emission of NOx and PM in the Euro V standard compared to the Euro III standard is 60% and over 90%, respectively.
