Keywords

1 Introduction

The consumption of petroleum-based diesel can be reduced by different alternate fuels. One of the alternate fuels is vegetable oil which is a renewable. This vegetable oil can be used in engines in different forms like straight vegetable oil, esterified vegetable oil, or blends of this with diesel. We have made an attempt to run the engine by using blends of esterified waste cooking oil. Many researchers are working on these vegetable oil blends to study the impact of it on the performance the engine. Shetty et al. [1], reported that with 40% blend with waste cooking oil, a pressurized kerosene stove will have more efficiency (at 1.5 bar) than with pure kerosene. Subramanian et al. [2] did study of effect of diethyl ether on direction injection CI engine running on water–diesel emulsion. They found that diethyl ether can significantly reduce smoke density and NOx levels without affecting the brake thermal efficiency. Tejesh et al. [3] performed test with blends of sesame and palm oil. They blended this dual biodiesel up to 40% in diesel. They found reduction in CO, HC, and without much reduction in efficiency. Kotebevi et al. [4] experimented by blending waste cooking oil biodiesel with diesel. They observed a considerable reduction in emissions like CO, UBHC, and smoke density with a small drop in thermal efficiency. Sunil Kumar et al. [5] did study with dual biodiesel. They used Simarouba and Neem biodiesel blends in diesel engine. They found reduction of HC and CO with percentage increase in blends. Kumar et al. [6] conducted study on CI engine at various compression ratio using ethanol–diesel blends. They found reduced smoke density, increase in NOx, and increase in thermal efficiency with increase in compression ratio. Krishna Murthy et al. [7] used canola oil blends for their study, and they found better performance with 30% blends. Korus et al. [8] studied the polymerization of vegetable oils. Agarwal et al. [9] investigated the effect of injection pressure and timing on the performance of Diesel engine with karanja biodiesel blends. They found that increase in injection pressure increases the thermal efficiency. Aldhaidhawi et al. [10] investigated the effect of 20% rape seed biodiesel blend on delay period, under full load at different engine speeds. They observed shorter ignition delay for the blend. Most of the literature mainly propose a low blending order upto 20% with pure diesel for optimum performance. In this work, the stress is given on higher blending order, say, 40% biodiesel mixed with diesel and the performance and emission.

2 Methodology

Waste cooking oil is the oil obtained after frying the food items. The vegetable oil will not be suitable for consumption after repeated frying of food items because of high FFA content. This waste cooking oil will be still viscous and cannot be used directly in engines. Viscosity of this oil has to be reduced by some methods. We used transesterification process after filtering the oil. Then, the blends were prepared with different percentages. Blends are designated as B0, B10, B20, B30, and B40 where the number represents the percentage of biodiesel in the blend. Different instruments like bomb calorimeter, Saybolt viscometer, open-cup apparatus, etc., are used to find the different properties of diesel and blends.

2.1 Properties of Biodiesel and Waste Cooking Oil

The different properties like viscosity, flash and fire point, calorific value, specific gravity, iodine value, FFA content, pour point, etc., of diesel and biodiesel are measured and are tabulated in Table 1. The properties like viscosity, calorific value, flash point, and fire point of blends are obtained and are tabulated in Table 2.

Table 1 Properties of fuels
Full size table
Table 2 Properties of biodiesel blends
Full size table

The viscosity for waste cooking oil biodiesel is measured at various temperatures, and a graph of viscosity vs. temperature is plotted in Fig. 1.

Fig. 1
figure 1

Temperature versus kinematic viscosity for waste cooking oil biodiesel

Full size image

2.2 Engine Specifications

Tests are conducted on single-cylinder, multi-fuel VCR engine. It is a four-stroke computer-based diesel engine coupled with eddy current dynamometer which can run on both petrol and diesel. The compression ratios can be varied from 6:1 to 10:1 for petrol and 14:1 to 20:1 for diesel. Provisions are made for mounting both spark plug and diesel injector on cylinder head. A PCB sensor is mounted on the top of the cylinder to measure the pressure inside the cylinder at different crank angles. Performance characteristics like thermal efficiency and specific fuel consumption are calculated, and emission characteristics measured are CO, HC, NOx, CO2, and smoke density. Tests are conducted at two different compression ratios (17.5 and 19) with pure diesel and blends, varying percentages from 10 to 40 at five different loads.

3 Results and Discussions

3.1 Performance Characteristics

The variation of specific fuel consumption with torque for compression ratio of 17.5 and 19 is shown in Figs. 2 and 3, respectively. It can be seen from the graph that the BSFC is lower for diesel at all compression ratios and increases as the blend amount is increased, and then, the specific fuel consumption is greater while varying the percentages of blend. BSFC of B10, B20, B30, and B40 is more than that of diesel at partial load. Higher compression results in better combustion which reduces the mass of fuel per unit brake power. But BSFC stayed more than diesel in case of waste cooking oil biodiesel diesel blends. Figure 2 shows the comparison of specific fuel consumption of blends with the diesel. The graph shows that B20 has better performance. The reason could be higher combustion efficiency for B20 blend at this compression ratio.

Fig. 2
figure 2

BSFC versus torque for compression ratio 17.5

Full size image
Fig. 3
figure 3

BSFC versus torque for compression ratio 19

Full size image

The variation of specific fuel consumption with torque for blends and diesel at compression ratio 19 is shown in Fig. 3. The graph shows that B30 has better performance. The reason could be higher combustion efficiency for B30 blend at this compression ratio.

The impact of torque variation on brake thermal efficiency (BTE) has been analyzed and is plotted in Figs. 4 and 5. A marginal reduction in thermal efficiency is observed with increases in percentages of blends. This is because of greater viscosity and lower calorific value of biodiesel blends. The effect of blending on brake thermal efficiency is shown in Fig. 4. It shows that B30 has the better performance compared to all other combinations.

Fig. 4
figure 4

Variation of brake thermal efficiency with torque for CR = 17.5

Full size image
Fig. 5
figure 5

Variation of brake thermal efficiency with torque for CR = 19

Full size image

The effect of blend percentage on thermal efficiency at different load is shown in Fig. 5. The graph shows that B30 has the better performance compared other blends.

3.2 Emission and Combustion Characteristics

Throughout the study, CO HC, CO2, and NOx emissions of the engine are obtained at different loads for all blends used. Figures 6, 7, 8, 9, 10, 11, 12, and 13 shows the variations of CO, HC, CO2, and NOx emissions for different blends used at different compression ratio. It shows that the CO emissions decreases with increase in compression because the combustion efficiency increases with compression ratio. Same time, increase in CO2 and NOx are observed because as the combustion efficiency increases combustion temperature also increases. This is the main reason for higher nitrogen oxides emissions. The CO and HC emissions were little higher for B10 blend.

Fig. 6
figure 6

CO emission results (CR = 17.5)

Full size image
Fig. 7
figure 7

HC emission results (CR = 17.5)

Full size image
Fig. 8
figure 8

CO2 emission results (CR = 17.5)

Full size image
Fig. 9
figure 9

NOx emission results (CR = 17.5)

Full size image
Fig. 10
figure 10

HC emission results (CR = 19)

Full size image
Fig. 11
figure 11

CO2 emission results (CR = 19)

Full size image
Fig. 12
figure 12

CO emission results (CR = 19)

Full size image
Fig. 13.
figure 13

NOx emission results (CR=19)

Full size image

Variations of cylinder pressure with crank angle for 100% diesel at different load is shown in Fig. 14. Figure (a) is for partial load and (b) for full load. It is observed that the peak pressure is 5° after TDC for this case.

Fig. 14
figure 14

Cylinder pressure variation versus crank angle

Full size image

It is noted that the peak pressure elevation rate at compression ratio 19 was approximately found to be 63 bars for 100% load, and the maximum pressure elevation rate is decreased with decrease in compression ratio. But in compression ratio 17.5, B20 shows the better performance, and the cylinder pressure is found to be 63.5 bars. Improved performance and cylinder pressure is found at compression ratio, and for blends the increase in pressure is also more [11, 12]. After getting all the results, we concluded that B40 shows the better performance as compared to standard diesel, as the cylinder/peak pressure are found to be 70 bar in compression ratio 19. When the peak cylinder pressures are compared for blends and pure diesel, blends resulted in higher peak pressure compared to pure diesel.

4 Conclusions

Single-cylinder, multi-fuel, constant-speed CI engine ran successfully with the biodiesel blends. The properties of fuel used are comparable with that of pure diesel. For blends, CO and HC are lower compared to diesel fuel. NOx and CO2 emissions are boosted by increasing the proportion of biodiesel in the blends because of higher combustion temperature. Increase in carbon dioxide and nitric oxide emissions are found with increase in compression ratio. When the performance characteristics are compared, B20 with compression ratio 17.5 gave better results compared with other blends. Increase in thermal efficiency with increase in compression ratio is observed, and thermal efficiency is found to be highest for 40% biodiesel blend. Variations of peak pressure with load and compression ratio are observed in p-Ɵ diagram.