**3. Control strategies for emissions in diesel engine**

The world is now aware of the environmental and human health costs of pollution from diesel engines, which form the bulk of commercial and personal public transport systems. **Table 1** shows that there is an increase in the regulatory measures on toxic gas emissions. These regulations oblige vehicle manufacturers and transport industry service providers to be motivated to work harder to meet the appropriate standards and regulations. Among the techniques that have been employed to cut down on emissions are EGR, LNT, DOC, DPF, and SCR [46, 47]. However, there is no single method that meets emission standards by the regulatory bodies on vehicular emission.

#### **3.1 Exhaust gas recirculation (EGR)**

This is one of the most useful and successful techniques in the control of and fight against diesel exhaust emissions. EGR allows the recirculation of part of the diesel exhaust into the combustion chamber, to reburn together with the fresh intake charge [49] as shown in **Figure 5**.

This technology has been able to reduce NOX emissions, but it causes an increase in UHC and CO emissions as compression temperatures decrease. It also affects engine thermal efficiency as shown in **Figure 6**. This technique has two methods for quantification of EGR flow rate, although there is no single method that is universally accepted. The two methods are the mass method and the gas concentration method [5]. These two methods are demonstrated in **Figure 5** and expressed in Eqs. (1) and (2):

$$\mathbf{r}\_{EGR} = \frac{\mathbf{\dot{m}\_{EGR}}}{\mathbf{\dot{m}\_{altr}} + \mathbf{\dot{m}\_{f}} + \mathbf{\dot{m}\_{EGR}}} \tag{1}$$

$$
\boldsymbol{\sigma}\_{EGR} = \frac{\dot{\mathbf{m}}\_{EGR}}{\dot{\mathbf{m}}\_{altr} + \dot{\mathbf{m}}\_{f} + \dot{\mathbf{m}}\_{EGR}} \tag{1}
$$

$$
\frac{[CO\_2]\_{int} - [CO\_2]\_{amb}}{[CO\_2]\_{ckh} - [CO\_2]\_{avol}} \approx \frac{[CO\_2]\_{int}}{[CO\_2]\_{ckh}} \tag{2}
$$

**41**

**Figure 6.**

**Figure 5.**

**Table 1.**

**3.3 The selective catalyst reduction (SCR)**

*EGR system nomenclature and control design for the EGR valve [4].*

This is one of the most recent technology developments introduced for the control of diesel exhaust emissions. This system was originally introduced to cater for HD engines [53], but Audi and Volkswagen have also adopted it for their

*Variation of engine thermal efficiency and NOX with the influence of EGR dilution [50].*

*Effects of Biodiesel Blends Varied by Cetane Numbers and Oxygen Contents on Stationary Diesel…*

**STD type CO g/kWh HC g/kWh NOX g/kWh PM g/kWh** Euro I 4.5 1.1 8.0 0.61 Euro II 4 1.1 7.0 0.15 Euro III 2.1 0.66 5.0 0.13 Euro IV 1.5 0.46 3.5 0.02 Euro V 1.5 0.46 2.0 0.02 Euro VI 1.5 0.13 0.4 0.01

*EURO standards for heavy-duty vehicles according to Delphi 2016–2017 as per Ref. [48]*

*DOI: http://dx.doi.org/10.5772/intechopen.92569*

where the *m*̇ *EGR* is the mass flow rate of the gas recirculated, *m*̇ *air* is the mass flow rate of fresh air, *m*̇ *<sup>f</sup>* is the mass flow rate of the injected fuel, and *rEGR* is the mass fraction of the recirculated exhaust gases. [*CO*2]*int* is the carbon dioxide at the intake side, [*CO*2]*amb* is the ambient carbon dioxide, [*CO*2]*exh* is the exhaust carbon dioxide (exit carbon dioxide).

#### **3.2 The low NOX trap (LNT)**

This system is also known as NOX storage reduction (NSR) and NOX absorber catalyst (NAC). It has three main components, namely, the oxidation catalyst with platinum (Pt), the NOX storage with barium (Ba), and the reduction catalyst with rhodium (Rh). The platinum catalyst is preferred as it reduces NOX emissions at very low temperatures while offering a stable reaction in the presence of sulfur and H2O [51, 52]. **Figure 7** shows the LNT three-stage catalytic process.

*Effects of Biodiesel Blends Varied by Cetane Numbers and Oxygen Contents on Stationary Diesel… DOI: http://dx.doi.org/10.5772/intechopen.92569*


**Table 1.**

*Numerical and Experimental Studies on Combustion Engines and Vehicles*

engines has now achieved a specific output of 70 kW<sup>−</sup><sup>1</sup>

**3. Control strategies for emissions in diesel engine**

[42, 43] as shown in **Figure 4**.

bodies on vehicular emission.

in Eqs. (1) and (2):

where the *m*̇

rate of fresh air, *m*̇

(exit carbon dioxide).

**3.2 The low NOX trap (LNT)**

**3.1 Exhaust gas recirculation (EGR)**

intake charge [49] as shown in **Figure 5**.

two-stage turbocharging, variable valve actuation, closed loop combustion control, and advanced model-based controls. Development in advanced diesel

pressure (BMEP) of 24 bars [41], hence meeting EURO VI emission standards

The world is now aware of the environmental and human health costs of pollution from diesel engines, which form the bulk of commercial and personal public transport systems. **Table 1** shows that there is an increase in the regulatory measures on toxic gas emissions. These regulations oblige vehicle manufacturers and transport industry service providers to be motivated to work harder to meet the appropriate standards and regulations. Among the techniques that have been employed to cut down on emissions are EGR, LNT, DOC, DPF, and SCR [46, 47]. However, there is no single method that meets emission standards by the regulatory

This is one of the most useful and successful techniques in the control of and fight against diesel exhaust emissions. EGR allows the recirculation of part of the diesel exhaust into the combustion chamber, to reburn together with the fresh

This technology has been able to reduce NOX emissions, but it causes an increase in UHC and CO emissions as compression temperatures decrease. It also affects engine thermal efficiency as shown in **Figure 6**. This technique has two methods for quantification of EGR flow rate, although there is no single method that is universally accepted. The two methods are the mass method and the gas concentration method [5]. These two methods are demonstrated in **Figure 5** and expressed

*rEGR* = \_\_\_\_\_\_\_\_\_\_\_\_\_ <sup>m</sup>̇ *EGR* ṁ *air* + ṁ *<sup>f</sup>* + ṁ *EGR*

≈ \_ [*CO*2]*int* [*CO*2]*exh*

*<sup>f</sup>* is the mass flow rate of the injected fuel, and *rEGR* is the mass

[*CO*2]*int* − [*CO*2]*amb* \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ [*CO*2]*exh* − [*CO*2]*amb*

*EGR* is the mass flow rate of the gas recirculated, *m*̇

fraction of the recirculated exhaust gases. [*CO*2]*int* is the carbon dioxide at the intake side, [*CO*2]*amb* is the ambient carbon dioxide, [*CO*2]*exh* is the exhaust carbon dioxide

This system is also known as NOX storage reduction (NSR) and NOX absorber catalyst (NAC). It has three main components, namely, the oxidation catalyst with platinum (Pt), the NOX storage with barium (Ba), and the reduction catalyst with rhodium (Rh). The platinum catalyst is preferred as it reduces NOX emissions at very low temperatures while offering a stable reaction in the presence of sulfur and

H2O [51, 52]. **Figure 7** shows the LNT three-stage catalytic process.

and a brake mean effective

(1)

(2)

*air* is the mass flow

**40**

*EURO standards for heavy-duty vehicles according to Delphi 2016–2017 as per Ref. [48]*

#### **Figure 5.** *EGR system nomenclature and control design for the EGR valve [4].*

**Figure 6.** *Variation of engine thermal efficiency and NOX with the influence of EGR dilution [50].*

#### **3.3 The selective catalyst reduction (SCR)**

This is one of the most recent technology developments introduced for the control of diesel exhaust emissions. This system was originally introduced to cater for HD engines [53], but Audi and Volkswagen have also adopted it for their

**Figure 7.** *The low NOX trap (LNT) with three of its operating modes [53].*

passenger vehicle and LD segments. The SCR system works by utilizing ammonia as a reductant in order to minimize NOX emissions in the diesel exhaust by releasing N2 and H2O. This system therefore undergoes two processes during the working cycle, namely, hydrolysis and thermolysis as in Eqs. (3) and (4) for hydrolysis and thermolysis, respectively [54, 55].

$$\text{HNCO} + \text{H}\_2\text{O} \rightarrow \text{NH}\_3\text{+ CO}\_2\tag{3}$$

$$(NH\_2)\_2CO \rightarrow NH\_3 + HNOO\tag{4}$$

**43**

**Figure 9.**

*Schematic of the working mechanism of a diesel particulate filter (DPF) [6].*

*Effects of Biodiesel Blends Varied by Cetane Numbers and Oxygen Contents on Stationary Diesel…*

The DPF filter requires care to avoid excessive saturation and build-up of backpressure, both of which are harmful for engine operation and durability and increase fuel consumption and engine stress levels leading to premature failure of the filter and engine. DPF systems have been in operation in diesel exhaust emission control since the year 2000, primarily for removing PM emissions through physical filtration. DPFs are like a honeycomb with silicone carbide or cordierite written chemically as 2*MgO* − 2 *Al* 2 *O* <sup>2</sup> − 5*Si O* 2. Both ends of the structure are blocked to force the particulate matter through the porous substrate walls, thus acting as a mechanical filtering system. These walls are made such that they offer little or no resistance to flow of exhaust gases while maintaining the power to collect particles

The DOC is manufactured with the sole purpose of reducing CO and UHC emissions through oxidation of the hydrocarbons that are absorbed into the carbon particles. The DOC consists of a metal or a ceramic structure with an oxide mixture also called the wash coat that contains aluminum oxide (Al2O3), cerium oxide (CeO2), zirconium oxide (ZrO2), and an active metal catalyst of either platinum, palladium, or rhodium [54], as shown in **Figure 10**. For HD and LD vehicles in Europe, the United States, and Japan, the DOC is the after-treatment emission control systems of choice. The DOC with a platinum metal catalyst is the most popular among manufacturers and consumers. However, the DOC has the disadvantage of reacting with sulfur oxide and sulfur trioxide producing sulfates and sulfuric acid,

4*NO* + 4*N H*<sup>3</sup> + *O*2 → 4 *N*<sup>2</sup> + 6 *H*2*O* (5)

2*NO* + 2*N O*<sup>2</sup> + 4*N H*3 → 4 *N*<sup>2</sup> + 6 *H*2*O* (6)

6*N O*<sup>2</sup> + 8*N H*3 → 7 *N*<sup>2</sup> + 12 *H*2*O* (7)

*DOI: http://dx.doi.org/10.5772/intechopen.92569*

**3.4 Diesel particulate filter (DPF)**

[56] as shown in **Figure 9**.

**3.5 Diesel oxidation catalyst (DOC)**

In addition to the two processes of hydrolysis and thermolysis, SCR undergoes other chemical reactions to complete its normal cycle, thus reducing the emissions of NOX further as in Eqs. (5)–(7). **Figure 8** shows a schematic diagram of an SCR system showing the oxidation catalyst, wall flow particulate filter, and the flow through the SCR catalyst. **Figure 8** also includes key components of a urea solution tank, a spray module, a static mixer, temperature, and NOX sensor, courtesy of Robert Bosch GmbH [46].

#### **Figure 8.**

*Schematic diagram of the SCR NOX control system as used in a standard production vehicle [46].*

*Effects of Biodiesel Blends Varied by Cetane Numbers and Oxygen Contents on Stationary Diesel… DOI: http://dx.doi.org/10.5772/intechopen.92569*

$$4\text{NO} + 4\text{NH}\_3 + O\_2 \to 4\text{N}\_2 + 6\text{H}\_2\text{O}\tag{5}$$

$$2NO + 2NO\_2 + 4NH\_3 \rightarrow 4N\_2 + 6H\_2O \tag{6}$$

$$6NO\_2 + 8NH\_3 \rightarrow 7N\_2 + 12H\_2O \tag{7}$$

#### **3.4 Diesel particulate filter (DPF)**

*Numerical and Experimental Studies on Combustion Engines and Vehicles*

passenger vehicle and LD segments. The SCR system works by utilizing ammonia as a reductant in order to minimize NOX emissions in the diesel exhaust by releasing N2 and H2O. This system therefore undergoes two processes during the working cycle, namely, hydrolysis and thermolysis as in Eqs. (3) and (4) for hydrolysis and

*HNCO* + *H*2*O* → *N H*<sup>3</sup> + *C O*<sup>2</sup> (3)

In addition to the two processes of hydrolysis and thermolysis, SCR undergoes other chemical reactions to complete its normal cycle, thus reducing the emissions of NOX further as in Eqs. (5)–(7). **Figure 8** shows a schematic diagram of an SCR system showing the oxidation catalyst, wall flow particulate filter, and the flow through the SCR catalyst. **Figure 8** also includes key components of a urea solution tank, a spray module, a static mixer, temperature, and NOX sensor, courtesy of

*Schematic diagram of the SCR NOX control system as used in a standard production vehicle [46].*

(*N H*2)2*CO* → *N H*<sup>3</sup> + *HNCO* (4)

thermolysis, respectively [54, 55].

*The low NOX trap (LNT) with three of its operating modes [53].*

**Figure 7.**

Robert Bosch GmbH [46].

**42**

**Figure 8.**

The DPF filter requires care to avoid excessive saturation and build-up of backpressure, both of which are harmful for engine operation and durability and increase fuel consumption and engine stress levels leading to premature failure of the filter and engine. DPF systems have been in operation in diesel exhaust emission control since the year 2000, primarily for removing PM emissions through physical filtration. DPFs are like a honeycomb with silicone carbide or cordierite written chemically as 2*MgO* − 2 *Al* 2 *O* <sup>2</sup> − 5*Si O* 2. Both ends of the structure are blocked to force the particulate matter through the porous substrate walls, thus acting as a mechanical filtering system. These walls are made such that they offer little or no resistance to flow of exhaust gases while maintaining the power to collect particles [56] as shown in **Figure 9**.

#### **3.5 Diesel oxidation catalyst (DOC)**

The DOC is manufactured with the sole purpose of reducing CO and UHC emissions through oxidation of the hydrocarbons that are absorbed into the carbon particles. The DOC consists of a metal or a ceramic structure with an oxide mixture also called the wash coat that contains aluminum oxide (Al2O3), cerium oxide (CeO2), zirconium oxide (ZrO2), and an active metal catalyst of either platinum, palladium, or rhodium [54], as shown in **Figure 10**. For HD and LD vehicles in Europe, the United States, and Japan, the DOC is the after-treatment emission control systems of choice. The DOC with a platinum metal catalyst is the most popular among manufacturers and consumers. However, the DOC has the disadvantage of reacting with sulfur oxide and sulfur trioxide producing sulfates and sulfuric acid,

**Figure 10.**

*Schematic diagram of a DOC and its operation in reducing emissions of CO and UHC through the process of oxidation [6].*

which shortens the service life of the emission control system besides the additional effects on the natural environment and human health.

Six factors affect and influence the choice of a DOC filter:

