Keywords

1 Introduction

The biggest challenge of the twenty-first century is the increasing amount of pollution in the atmosphere. The major sources of air pollution from the combustion of fossil fuels are NOx, CO, CO2 [1, 2]. These harmful emissions are disrupting the complex, dynamic natural gaseous system of our atmosphere that supports life. Oxides of nitrogen and carbon cause severe environmental problems like acid rain, ozone layer depletion, global warming, etc. [3]. But, among all these oxides NOx is the biggest concern. One study reported that the contribution of automobile in NOx emission is 49% and from power plant is 46% [4]. Report also claims that as the NOx level gets doubled into the atmosphere the ozone layer is depleted by 12% and atmospheric temperature rises by 0.3 [5, 6]. Government has imposed stringent norms on automobile industries to reduce the amount of exhaust emissions. In India, Bharat Stage 6 is on the verge of getting applied. So, several researches are going on for purification of auto exhaust by using catalytic devices. In NOx catalyst research, two reaction procedures have been proposed; direct decomposition reaction and reduction [7,8,9,10]. The reaction rate of direct decomposition is very slow, so application of this scheme is hardly considered. Whereas reduction reaction is comparatively fast and it takes place in presence of CO, H2, and hydrocarbons as reducing agent which are present in exhaust gases [11]. Many technologies have been developed to use these simple reaction schemes for auto exhaust reduction. Catalytic convertor is one of the technologies that are presently working in this context. It is a device used to reduce vehicular emissions by conducting two simple chemical reaction processes, i.e., reduction of NOx and the oxidation of hydrocarbons and carbon monoxide, by using the catalyst platinum, palladium, and rhodium [12, 13]. The basic reactions that occur inside the catalytic converters are [14]

$$ 2{\text{CO}} + {\text{O}}_{2} \to 2{\text{CO}}_{2} $$
(1)
$$ 2{\text{NO}} \to {\text{O}}_{2} + {\text{N}}_{2} $$
(2)
$$ 2{\text{NO}}_{2} \to {\text{N}}_{2} + 2{\text{O}}_{2} $$
(3)
$$ {\text{HC}} + {\text{O}}_{2} \to {\text{CO}}_{2} + {\text{H}}_{2} {\text{O}} $$
(4)

The use of these platinum-grade material has dominated in reducing the vehicular pollution, but they all are very rare and therefore costly [15,16,17]. Thus, it leads to the development of technologies that can explore other cheap sources and methods to reduce the vehicular emission. Some of the promising researches have been observed in the development of the catalytic materials, which includes ammonia-based catalysts, carbon-supported catalysts, silica catalysts, zeolite-based catalysts like ruthenium zeolite catalyst [18,19,20,21,22]. Of late split injection strategy has drawn the attention of the researcher due to its effective NOx reduction capacity along with reduction in soot formation and piston work trade-offs [23]. Studies show that oxides like cerium oxide (CeO2) and titanium oxide (TiO2) have good redox properties. M. S. Hedge in 2010 proposed preparative method to form catalysts of different combinations of CeO2 and TiO2 with the noble metals like platinum, palladium, and rhodium [24]. In 2006, Nitin Labhsetwar studied the application of perovskite-type catalysts with ABO3-type structure which posses very good thermal stability characteristics [25]. Clearly, the efforts were made to reduce the cost of catalytic converter without compromising with the catalytic activity. However, in the year 2010, S. Chauhan expressed his views on the noble metals like platinum, palladium, and rhodium which are the best option available for reducing the exhaust emissions, although they are very expensive and in a limited supply [26]. He also studied the different catalysts like iridium, copper, ruthenium, zeolite, and nickel. N. Nedunchizehian in his paper shows the effects of nickel–copper alloy in the reduction of the oxides of nitrogen in the diesel engine exhaust [27,28,29]. The alloy used was Monel which includes 65% nickel, 33% copper, and 2% other elements. Their study shows 70% reduction in oxides of nitrogen and it has been concluded that the efficiency of the conversion is dependent upon the bed temperature.

In this paper, a similar study has been conducted with the sole purpose of reducing the consumption of expensive platinum-grade material. Thus, it reduces the cost of the catalytic converters without compromising with its conversion efficiency. For this purpose, the study is strictly based on the material to be used in the monolith substrate. Here, we are using the nickel–copper alloy, i.e., constantan as a catalyst which includes 45% nickel, 55% copper, and no other alloying elements. A device has been fabricated using constantan wire as a newly developed monolith. Experimental study is done to check the percentage conversion of oxides of nitrogen, carbon monoxide, and hydrocarbon.

2 Materials and Methods

The exhaust reducing device is fabricated in two parts; inner monolith of constantan wire mesh and outer casing made of aluminum. The monolith is made of galvanized iron wire net structure of dimension (500 × 160) mm in which constantan wire of 0.5 mm thickness (See Fig. 1a) is weaved throughout. Constantan wire of 200 and 150 mm length is cut and weaved through every alternate hole of the GI wire mesh. The mesh density is kept high to offer maximum surface area for reaction to take place. The monolith is coated with a layer of calcium sulfate hemihydrate to hold the mesh in structure and to enable maximum heating inside the monolith. A 3 mm layer of rubber coating is given over the surface of the monolith to absorb maximum shocks in operating condition.

Fig. 1
figure 1

Image of a constantan wire b fabricated device

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The outer casing is made of aluminum sheet metal of thickness 2 mm (See Fig. 1b). The structure of the outer casing is kept similar to the presently used catalytic converter. The dimensions of the fabricated device are shown in Fig. 2. The total length of the device is 400 mm with the inlet and outlet diameters of 56 mm. The mesh view of Fig. 1 shows the arrangement of the constantan wire such that the cross-link arrangement of the wires forms very fine square with the sides of 2 mm.

Fig. 2
figure 2

Drafting of the device showing dimensions

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Here in Fig. 3 point 1 shows the inlet section of the device, and this section is attached to the exhaust pipe of the engine. Point 2 shows the outer aluminum casing of the device. This metal covering supports the inner components and protects the device from any mechanical damage. Point 3 shows the layer of rubber cladding applied below the metallic casing to damp mechanical vibrations. Also, it seals exhaust gases from escaping the wire mesh inside the device. Point 4 shows the layer of calcium sulfate hemihydrate enclosing the wire mesh. This layer provides thermal insulation to the device. Point 5 shows the dense copper–nickel alloy (constantan) wire mesh. This mesh acts as the catalyst for the reaction to occur. Following reaction take place in presence of constantan as catalyst:

$$ {\text{NO}} + {\text{CO}} \to \frac{1}{2}{\text{N}}_{2} + {\text{CO}}_{2} $$
(5)
$$ {\text{C}}_{{\text{n}}} {\text{H}}_{{\text{m}}} + \left( {2{\text{n}} + {\text{m}}/2} \right){\text{NO}} \to \left( {{\text{n}} + {\text{m}}/4} \right){\text{N}}_{2} + {\text{nCO}}_{2} + {\text{m}}/2{\text{H}}_{2} {\text{O}} $$
(6)
$$ {\text{NO}} + {\text{H}}_{2} \to \frac{1}{2}{\text{N}}_{2} + {\text{H}}_{2} {\text{O}} $$
(7)
Fig. 3
figure 3

Schematic diagram of a front view b side view of the device

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Point 6 shows the outlet section of the device. This section can either be exposed to the atmosphere or can be attached to the catalytic converter as per the requirements of the user.

3 Experimental Procedure

In order to measure the reduction efficiency of the newly fabricated device with constantan as a monolith, the device is fitted to the exhaust tailpipe of a water-cooled single cylinder direct injection engine. The specifications of the engine are given in Table 1. The experimental schematics are shown in Fig. 4. The NOx, CO, and HC emissions are measured by AVL DGAS 444 analyzer. The fuel flow is measured with the help of the burette and stopwatch. The device is fitted to the exhaust system and no leakage is verified. The engine is run at a constant 1500 rpm at no load condition for 1 h. At the initial stage, the engine and the device are allowed to get heated up to avoid any cold starting problem. The AVL DGAS 444 analyzer is used first to record the emissions of NOx, CO, and HC without the device and then the same is recorded with the device attached. All the readings are recorded for 15 min duration and the same is tabulated and compared graphically.

Table 1 Engine specifications
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Fig. 4
figure 4

Schematic diagram of the experimental setup and photograph of the experiment

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AVL DGAS 444 Gas Analyzer Calibration. Before performing the emission testing, the gas analyzer is run through several testing procedures to ensure correct functioning. These tests are a prerequisite to its working.

Leak test. The gas in port is covered by the thumb and leak test is run. After 30 s, the leak test confirmation is achieved. In case of any anomaly, the error message is shown on the screen.

Residual Test. Soon after the leak test, residual test is checked. This test is done to ensure complete evacuation of any residual exhaust particles inside the channel of the analyzer. After positive residual test, calibration of the analyzer is required.

IRO Sensor Calibration Test. This test is run to calibrate various sensors in the analyzer like oxygen sensor, etc. with the ambient condition.

Hydrocarbon Residual Test. This test is run to ensure the complete absence of any particulate matter of any hydrocarbon residue inside the analyzer system.

After performing the entire abovementioned test, the AVL DGAS 444 gas analyzer is ready to be used for emission testing. All the parameters are set with respect to ambient conditions.

4 Results and Discussions

Experimental investigations are carried out and variations of exhaust emissions in the form of NOx, CO, and HC are graphically represented with respect to time factor at a constant 1500 rpm at no load condition.

The conversion efficiency of the device is calculated by the following formula:

$$ \frac{{{\text{Emissions without device}} - {\text{Emissions with device}}}}{{{\text{Emissions without device}}}} \times 100\% $$

4.1 Effect of Device on NOx Reduction

Emission testing shows a significant reduction in NOx with the use of the device. All the emissions are recorded with respect to time. At time t = 1 min, the conversion efficiency of the device for NOx is 76%, which fluctuates till 60% at the end of 15 min and then get stabilized. The increase in conversion efficiency is because with time the device also gets heated up. For the reaction to take place, the device needs to reach its light-off temperature. So as the device reaches its maximum efficiency it gets stabilized. The emissions of NOx with and without device with respect to time are plotted in Fig. 5.

Fig. 5
figure 5

Variation in NOx emissions with and without device w.r.t. time in minutes

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4.2 Effect of Device on Hydrocarbon Conversion

The device shows a significant reduction in emissions of hydrocarbon. The reduction of NOx starts from 57.45% at time t = 1 min and get stabilized at 35% at the end of 15 min. The emissions of HC with and without device with respect to time are plotted on Fig. 6.

Fig. 6
figure 6

Variation in HC emissions with and without device w.r.t. time in minute

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4.3 Effect of Device for Carbon Monoxide Conversion

The device shows a remarkable reduction in emissions of CO. At the beginning of emissions testing, the oxidation of CO was recorded as 63.33% which undergoes slight fluctuation with time and get stabilized at 60.11% at the end of time t = 15 min. The emissions of HC with and without device with respect to time are plotted in Fig. 7.

Fig. 7
figure 7

Variation in CO emissions with and without device w.r.t. time in minutes

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4.4 Comparison of Percentage Conversion Efficiency of the Device

The device shows significant results for NOx, CO, and HC conversion. Results also show evident fluctuation of emissions with time. Figure 8 represents the percentage conversion efficiency variation for CO, HC, and NOx, respectively, with time.

Fig. 8
figure 8

Comparison of conversion efficiency of CO, HC, and NOx w.r.t. time

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5 Conclusion

Based on the results it can be inferred that the device shows significant reduction in exhaust emissions when tested on a single cylinder diesel engine. NOx, CO, and HC emissions are reduced by 60, 60, and 35% approx, respectively. During experimental investigation, the device generates no back pressure, so the loss in engine efficiency does not come into existence. Further, the cost analysis of the device shows that the manufacturing of the device is cheap. This device can be utilized as a partial replacement or as an add-on with the presently used three-way catalytic convertor. This will ensure less use of the platinum-grade materials like platinum, palladium, and rhodium in the present catalytic convertor with its improved efficiency. Also, this device can be used in other standalone power generating IC engine units where no catalytic converters are used. The above study tries to work on a noble cause of pollution reduction from auto exhausts and shows promising results for future application of it in the automobile market.