Impact of variable exhaust valve timing on diesel engine characteristics fueled with waste cooking oil biofuel blends: A numerical analysis

Abstract

The quantity of the conventional sources of energy such as petroleum, coal, and the deposits of hydrocarbon are limited in nature. The rapid growth is observed in the industrial and transportation section due to increase in population that has compelled the mankind to look for an alternative to conventional fuels. Biodiesel can be a potential substitute due to its ease of availability, accessibility, lower cost, and nontoxic characteristics. In this study, waste cooking oil (WCO) as the feedstock for biodiesel due to its abundance and low prices is chosen. It has been observed that the high prices of cooking oil have compelled people to reuse it multiple times, which can have negative health consequences such as inflammation, cholesterol issues, diabetes, and cancer. However, if people can obtain WCO at a reasonable cost, they will refrain from reusing it repeatedly. This article presents a numerical method that investigates the effects of variable exhaust valve timing on the performance, emissions, and combustion parameters of WCO and its different blends in a conventional mechanical fuel injection system diesel. The study was conducted using a single-cylinder, water-cooled, in-line diesel engine running at a constant speed. As, it is not possible to determine the values of engine performance, emissions, and combustion parameters for different valve timings experimentally, a numerical method has been adopted. The valve timing range was taken as 46–66° before bottom dead center (BDC) for exhaust valve opening and 6–20° after top dead center (TDC) for exhaust valve closing and the inlet valve opening and closing are constant at 16° b TDC and 33° a BDC, respectively.

Keywords

Biodiesel biofuel diesel engine performance characteristics combustion and emission

Introduction

Traditional energy sources currently serve as the primary sources of energy, but the imminent scarcity is a consequence of increased usage. Biodiesel is currently considered potential energy resource to completely replace petroleum fuel. The key features that an alternative fuel should possess include cost-effectiveness, convenient availability, and fewer environmental hazards as compared to traditional fuels. Biodiesels meet all of these parameters. According to the 2012 report by EASAC, biodiesel classification is primarily based on its origin, categorized as first, second, and third generation.^1,2 Biomass is produced using organic crops. In the recent scenario, various methodologies or technologies exist for producing biodiesel and bioethanol. The selection of a particular energy crop for biomass conversion mainly depends on energy efficiency and greenhouse gas (GHG) emissions.^3–7 The first-generation biofuels are easily obtainable from edible feedstocks, such as mustard oil, olive oil, rapeseed oil, palm oil, rice oil, etc. However, producing biodiesel from edible food resources can be detrimental to food availability. The disadvantages of using first-generation feedstocks have prompted researchers to focus on non-edible feedstocks. Second-generation biofuels, on the other hand, are produced from non-consumable feedstocks, including neem oil, Calophyllum inophyllum oil, Karanja oil, rubber seed oil, Jatropha oil, Nagchampa oil, Madhuca indica oil, etc. Some of the major non-edible plants, such as Jatropha oil, Jojoba oil, and Karanja oil, experience a decline in productivity when used for second-generation fuels. These raw materials can be grown on marginal lands.^8–10 For this reason, non-edible crops are intended to be grown on agricultural land, which has an immediate impact on the society's economy and food production. The disadvantages of second-generation biodiesel also include the requirement for higher amount of alcohol. To address the socioeconomic problems associated with non-edible oil, researchers are focusing on third-generation biodiesel, which are economically justified and more readily accessible. Biodiesel produced from microalgae and waste oils is referred to as third-generation biodiesel. The major benefits of third-generation biodiesel include fewer environmental issues, improved quality and yield, reduced competition for agricultural land, a higher percentage of oil, and a lesser impact on food stocks.^11,12 The main sources for third-generation biodiesel include fish oil, waste cooking oil (WCO), animal fat, microalgae, etc.¹³ These viable third-generation biodiesel resources surpass the feedstocks of previous generations in terms of availability, adaptability to environmental challenges, and financial feasibility.¹⁴ In this study, third-generation biodiesel is used because it is easily available and made from discarded frying oil, which serves as a feedstock for WCO biodiesels. Due to the increasing prices of edible oil, some people resort to repeatedly using WCO, which has adverse effects on their health. However, if this oil is used to produce biodiesel, people will not continue reusing it since they can obtain it at a reasonable cost. There is few literature on the influence of variable valve timing on diesel engine performance, combustion, and emission characteristics. Therefore, this study examines and compares the impact of variable valve timing on the performance, combustion, and emission characteristics of WCO and its mixtures with diesel using a single-cylinder diesel engine operating at a constant speed. Since it is not feasible to experimentally determine the engine's performance, emission, and combustion characteristics at various valve timings, a numerical methodology has been employed.

Proposed methodology

In this study, the characteristics of biodiesel and its blends made from WCO were determined through experimental testing, while some properties were also obtained from previous research. The performance, emissions, and combustion parameters of the compression–ignition (CI) engine depend on the chemical composition of the fuels. Fuel characteristics for biodiesel, WCO, and its mixtures are listed in Table 1.

Table 1.

Physicochemical characteristics of WCO biodiesel and its blends.^15–20

S. no.	Properties	Unit	Diesel	WCO100	WCO30	WCO20	WCO10
1	Cetane number		48	49.15	48.75	48.62	48.35
2	Density	kg/m³	830	884.29	846.33	840.71	834.28
3	Low heating value	MJ/kg	43.286	37.114	40.738	41.301	41.684
4	Kinematic viscosity (at 40°C)	mm²/s	2.542	4.915	3.301	3.084	2.753
5	Activation energy	kJ/mol	22	12	20	21	22
6	Surface tension factor	N/m	0.028	0.0433	0.03436	0.03122	0.028
7	Fuel thermal capacity	J/kg*K	1853	1853	1853	1853	1853
8	Diffusion factor (at atmospheric conditions)	s	3.10E-10	3.10E-10	3.10E-10	3.10E-10	3.10E-10
9	Fuel temperature	K	380	380	380	380	380
10	Saturated vapor pressure at low temperature (480 K)	bar	0.0477	0.001	0.0372	0.04091	0.04332
11	Saturated vapor pressure PV at critical temperature (710 K)	bar	1.616	1.576	1.6	1.605	1.61

Engine specifications

With the assistance of the Diesel-RK numerical tool, all numerical models for the performance, combustion, and emission characteristics at various valve timings were implemented. The engine specifications were defined for a single-cylinder, direct-injection, water-cooled, in-line, four-stroke diesel engine. Aluminum was chosen as the material for the piston head and cylinder head. The iterations were conducted at a nominal speed of 1500 rpm, a compression ratio of 17.5, and a top clearance of 1 mm under full load conditions. Table 2 presents the specifications for the test engines. An ambient pressure of 1 bar and temperature of 288 K was selected. The fuel injection started at 23⁰ before top dead center (TDC) with a maximum injection pressure of 220 bar. Table 3 summarizes all parameters related to fuel injection. Variable valve timings for the intake and exhaust valves were investigated, and Table 4 provides details of the valve timing range for both valves.

Table 2.

Engine specifications.

Parameters	Value
Engine type	Single-cylinder, four-stroke
Cooling system	Water cooled
Lubrication	Forced
Valve timing	Variable
Bore	80 (mm)
Stroke	110 (mm)
Connecting rod length	235 (mm)
Compression ratio	17.5
Speed	1500 (rpm)
Cylinder head design	Two valves
Cylinder wall thickness	5.6 (mm)
Material of cylinder head and piston head	Aluminium
Mean temperature of cylinder liner (at TDC)	400 (K)
Top clearance (at TDC)	1 (mm)
Piston	Bowl shape
Incentric piston bowl depth	21.8 (mm)
Intake manifold length	160 (mm)
Intake manifold diameter	38.1 (mm)
Exhaust manifold length	160 (mm)
Exhaust manifold diameter	34 (mm)
Diameter of pipe which deliver air to manifold	38.1 (mm)

Table 3.

Fuel injection details.

S. no.	Parameter	Value
1	Injection duration	29 CA
2	Maximum injection pressure	220 bar
3	Injection timing	23° b TDC
4	Injector nozzles bore	0.22 (mm)
5	No. of nozzles	3
6	Nozzle discharge coefficient	0.77
7	Distance between spray center and bowl axis	2.5 mm
8	Air fuel equivalence ratio	1.75
9	Ambient pressure	1 bar
10	Ambient temperature	288 K
11	Load	100%

Table 4.

Valve timing range.

Valve description	Valve timing range (°)
EVO (before BDC)	46–66
EVC (after TDC)	6–20
IVO (before TDC)	16 (constant)
IVC (after BDC)	33 (constant)

Experimental procedure

In this investigation, the performance, emission, and combustion parameters of various WCO biodiesel blends were computed at different valve timings of the exhaust valve. To begin with, the exhaust valve opening (EVO) was varied within the range of 46–66° before bottom dead center (b BDC), while the intake valve closure (IVC), intake valve opening (IVO), and exhaust valve closure (EVC) remained constant at 33° a BDC, 16° b TDC, and 15° a TDC, respectively. By comparing all the output parameters for each blend at different EVOs, the most effective EVO was selected and designated as the optimum EVO. Next, the EVC was varied within the range of 6–20° a TDC, while the EVO was kept constant at the optimum value for the corresponding blends, and the remaining valve timings remained unchanged. By comparing all the output parameters for each blend at different EVCs, the optimum EVC was determined.

Numerical method

The simulation program used in this investigation is Diesel-RK. The program includes equations that take into account and describe various factors, such as mass conservation, energy conservation, friction model, heat model, and NO_X model.^21–30

Conservation of mass

Equations are used to represent mass conservation, which is the net flux of mass across the system boundary²¹:

\frac{d m}{d t} = \frac{m_{i}}{m}

(1)

\frac{d (m_{i} Y)}{d t} = \sum_{j} m_{j} Y_{i}^{j} + {\dot{S}}_{g e n}

(2)

{\dot{S}}_{g e n} = Ω_{i} W_{m} v

(3)

{\dot{Y}}_{i} = \sum_{j} (\frac{{\dot{m}}_{j}}{m}) (Y_{i}^{j} - Y_{i}^{c y l}) + \frac{Ω_{i} W_{m}}{ρ}

(4)

Energy conservation

Equation contains the energy calculation that Fivelend and Assanis reported.²²

\frac{d (m u)}{d t} = - p \frac{d v}{d t} + \frac{d Q_{h t}}{d t} + \sum_{j} {\dot{m}}_{j} h_{j}

(5)

Brake mean effective pressure

The engine's brake mean effective pressure (BMEP) is determined by adding the indicated mean effective pressure and the mean pressure of the pumping strokes. Pumping mean effective pressure (PMEP) for friction losses mean effective pressure for friction PFR or friction mean effective pressure (FMEP).²³

BMEP = IMEP + PMEP – FMEP

(6)

Engine friction losses are computed as mean pressure of friction losses FMEP depending on the mode of operation:

FMEP = p_{f r} = A C_{m} + B p

(7)

where A is the bare empirical coefficients; C_m is the mean piston speed, m/s; p is the mean cylinder pressure, bar.

Specific fuel consumption

Specific fuel consumption (SFC) is calculated by the ratio of the mass flow rate of fuel and brake power of engine.²³

S F C = \frac{{\dot{m}}_{f}}{B P}

(8)

where

{\dot{m}}_{f}

is the mass flow rate of fuel and BP is brake power.

Brake torque

Torque is related to work by $2 π τ = W_{b}$ .²³

τ = \frac{(BMEP) V_{d}}{4 π}

(9)

where V_d is the displacement volume.

Indicated efficiency

η_{i n d} = \frac{I P}{{m_{f}}_{v}^{\dot{C}}}

(10)

where IP is indicated power and C_v is the calorific value of fuel.²⁴

Mechanical efficiency

Mechanical efficiency is calculated by the ratio of BP to IP.²⁴

η_{m e c h} = \frac{B P}{I P}

(11)

Volumetric efficiency

η_{v o l} = \frac{m_{a}}{ρ_{a} V_{d}}

(12)

where m_a is the mass of air entered the cylinder for one cycle;

ρ_{a}

is the air density evaluated outside the engine.²⁴

Heat transfer factor in cooling system

The value of the heat transfer factor in the cooling system strongly depends on the temperature difference between the wall and the boiling point of the liquid. When the temperature difference is significant, which is typical for engines that are thermally non-loaded, the heat transfer factor (hc_cool) can be calculated using Zonneken's formula, which takes into account the average velocity of the cooling liquid Ww²⁵:

h c_{cool} = 200 + 1500 (W_{w})^{0.5}

(13)

The heat transfer factor is computed as follows:

\begin{aligned} h c_{c o o l}^{'} = {h c_{c o o l}; i f Δ t > 46 h c_{c o o l} + f (Δ t); \\ i f 6.4 \leq Δ t \leq 46 h c_{c o o l} + 10198; \\ i f Δ t < 6.4 \end{aligned}

(14)

where Δt = T_Boil − T_W is a difference between boiling point and wall temperature.

f (Δ t) = 0.24 Δ t^{3} – 20.449 Δ t^{2} + 225.48 Δ t + 9530

(15)

No_x formation

When simulating the formation of nitrogen oxides, it is assumed that the cylinder is divided into two zones: the zone of fresh charge and the zone of burnt gas. The zone of fresh charge consists of air, fuel, and residual gas. Before combustion, the fresh charge zone exists alone. During combustion, the volume of the burnt gas zone increases. In calculating the combustion process, it is assumed that the local air-fuel equivalence ratio during combustion varies linearly from the initial value AFini < 1 up to 1.²⁶

Soot formation

The rate of soot formation in a burning zone is²⁷

{(\frac{d {[C]}^{-}}{d τ})}_{K} = 0.004 \frac{q_{c}}{V} \frac{d x}{d τ}

(16)

where V is the current volume of cylinder; q_c is a cycle fuel mass; dx/dt is a heat release rate.

Soot formation rate due to high-temperature thermal polymerization of drops nuclei is proportionate to rate of disappearance of drops because of full evaporation. In different processes, one is calculated with different equations.

At injection period:

{(\frac{d [C]}{d τ})}_{π} = 1.7 \frac{q_{c}}{V} \frac{1 - e x p [- {(\frac{\sqrt{K τ}}{d_{32}})}^{n^{'}}]}{τ_{e n p}}

(17)

where t is the current time from injection beginning, t_bnp is an injection duration, n′ is a factor of distribution (for diesel injectors: n′ = 2..4), K is a constant of evaporation, d₃₂ is the mean Sauted diameter of drops.

After injection termination:

{(\frac{d [C]}{d τ})}_{π} = 0.0028 (1 - x_{x e n p}) \frac{n^{'} q_{c}}{2 V τ_{2}} {(\frac{\sqrt{K τ}}{d_{32}})}^{n^{'}} e x p - {(\frac{\sqrt{K τ}}{d_{32}})}^{n^{'}}

(18)

where t₂ is the current time after injection termination; x_kbnp is a fraction of heat released at the end of injection.

Rate of soot burning:

{(\frac{d [C]}{d τ})}_{B} = 3.1 10^{- 6} n^{0.5} p [C]

(19)

where p is a current cylinder pressure, Mpa; [C] = C/V is a current soot concentration in cylinder.

Rate of soot concentration decrease because of expansion:

{(\frac{d [C]}{d τ})}_{V} = 0.75 \frac{6 n}{V} \frac{d V}{d φ} [C]

(20)

Resulting rate of soot formation and burning:

\frac{d [C]}{d τ} = B {(\frac{d [C]}{d τ})}_{K} + B {(\frac{d [C]}{d τ})}_{π} - \frac{1}{B} {(\frac{d [C]}{d τ})}_{B} - {(\frac{d [C]}{d τ})}_{V}

(21)

where

B = A {(\frac{n_{n o m}}{n})}^{m}

(22)

is an empiric factor; n is RPM; n_nom is RPM at full capacity; A, m are calibrated coefficients.

Exhaust gas soot concentration related to normal conditions:

[C]_{H} = \int_{φ}^{480} \frac{d [C]}{d τ} \frac{d φ}{6 n} {(\frac{0.1}{p_{480}})}^{\frac{1}{k}}

(23)

where p₄₈₀ is a cylinder pressure at 60° b BDC, k is an exhaust gas adiabatic exponent (1.33).

So_x formation

In the oxidization of sulfur, basic reactions are²⁴:

S + H_{2} \to H_{2} S

(24)

S + O_{2} \to S O_{2}

(25)

S O_{2} + O \to S O_{3}

(26)

2 S O_{2} + O_{2} \to 2 S O_{3}

(27)

S O_{3} + H_{2} O \to H_{2} S O_{4}

(28)

Results and discussions

Performance characteristics

There are several combustion characteristics which are calculated in this study.

Brake mean effective pressure

It shows a gradual increment upto the certain limit after that it decreases with the increment in the EVO and EVC. The BMEP of biodiesel and its blends is found to be lower value than that of diesel. The average uniform pressure on the piston as it transitions from TDC to BDC is known as BMEP It is the result of the mechanical efficiency and mean effective pressure formula in mathematics. The work completed per unit displacement volume of an engine defines BMEP.²⁶ It depends on elements like the engine's volumetric efficiency, density of the intake charge, and compression ratio.

On comparing the values of BMEP for WCO10 at different values of EVO, it was found that the max. and min. values of BMEP are 6.238 and 6.2098 bar, which were found when the exhaust valve was opened at 60 and 46° b BDC. Similarly, the maximum value of BMEP for WCO20, WCO30, and WCO100 was recorded as 6.2646, 6.2116, and 5.9469 bar, respectively, at an EVO of 60, 62, and 60° b BDC, respectively. The minimum value of BMEP for WCO20, WCO30, and WCO100 was found to be 6.2288 bar at 46° b BDC, 6.1787 bar at 48° b BDC, and 5.9136 bar at 46° b BDC, respectively. For diesel, the maximum BMEP was recorded as 6.5238 bar, found at 64° b BDC. Among all the blends of WCO biodiesel, the BMEP for WCO20 was found closest to diesel at 60° b BDC, which is about 3.973% lower than diesel (Figure 1).

Figure 1.

Variations in the BMEP with different fuel blends at the exhaust valve timings (a) EVO, (b) EVC.

Brake torque

The torque obtained at the transmission end of the crankshaft after eliminating the frictional and pumping losses, brake torque (BT) is the term for the force used to calculate braking power (Figure 2).

Engine load causes an increase in BT while engine speed causes a drop. Additionally, decreased fuel calorific value and fuel consumption during ignition have an impact on it.

Due to their lower calorific content, BT of biodiesel and its blends is found to be lower than diesel.

On comparing, WCO10 at different values of EVO, it was found that the max. and min. values of BT are 27.449 and 27.325 Nm, which were found when the exhaust valve was opened at 60 and 46° b BDC.

Optimum results were obtained at an EVO of 60° b BDC for WCO10, 60° b BDC for WCO20, 62° b BDC for WCO30, and 60° b BDC for WCO100.

The optimum value of EVC was obtained at 10° a TDC for WCO10, 10° a TDC for WCO20, 12° a TDC for WCO30, and 14° a TDC for WCO100.

Figure 2.

Variations in the BT with different fuel blends at the exhaust valve timings (a) EVO, (b) EVC.

Similarly, the maximum value of BT for WCO20, WCO30, and WCO100 was recorded as 27.566, 27.333, and 26.168 Nm, respectively, at an EVO of 60, 62, and 60° b BDC, respectively. The minimum value of BT for WCO20, WCO30, and WCO100 was found to be 27.409 Nm at 46° b BDC, 27.188 Nm at 48° b BDC, and 26.022 Nm at 46° b BDC, respectively. For diesel, the maximum BT was recorded as 28.707 Nm, found at 64° b BDC. Among all the blends of WCO biodiesel, the BT for WCO20 was found closest to diesel at 60° b BDC, which is about 3.975% lower than diesel. In the second step, when the EVC was kept variable and the EVO was set at the optimum for the corresponding blends. The maximum values of BT for WCO10, WCO20, WCO30, and WCO100 were found to be 27.715 Nm at 10° a TDC, 27.645 Nm at 10° a TDC, 27.485 Nm at 12° a TDC, and 26.317 Nm at 14° a TDC, whereas the minimum values of BT were found to be 27.269 Nm at 20° a TDC, 27.138 Nm at 20° a TDC, 27.2 Nm at 6° a TDC, and 26.119 Nm at 6° a TDC, respectively. When all the blends of WCO biodiesel were compared, it was found that the BT for WCO10 is closest to diesel at 10° a TDC, which is about 3.63% lower than diesel, as the maximum BT for diesel is 28.759 Nm found at an EVC of 12° a TDC.

Piston engine power

Piston engine power (PEP) is the power available at engine crankshaft for doing useful work. It is also known as brake power or engine output power (Figure 3).

While using diesel fuel, due to its high calorific value, which results in more efficient burning in the combustion chamber and greater PEP compared to biodiesel.^30,31

Low power performance while using WCO biodiesel and its blends is decreasing the PEP due to their lower heating value, increased viscosity, and density, which cause fuel flow issues and poor combustion efficiency.³²

A reduction in the PEP was found with the increasing blend ratio of biodiesel.

Optimum results were obtained at an EVO of 60° b BDC for WCO10, 60° b BDC for WCO20, 62° b BDC for WCO30, and 60° b BDC for WCO100.

The optimum value of EVC was obtained at 10° a TDC for WCO10, 10° a TDC for WCO20, 12° a TDC for WCO30, and 14° a TDC for WCO100.

Figure 3.

Variations in the PEP with different fuel blends at the exhaust valve timings (a) EVO, (b) EVC.

On comparing values of PEP for WCO10 at different values of EVO, it was found that the max. and min. values of PEP are 4.3114 and 4.2919 kW, which were found when the exhaust valve was opened at 60 and 46° b BDC. Similarly, the maximum value of PEP for WCO20, WCO30, and WCO100 was recorded as 4.3298, 4.2931, and 4.1102 kW, respectively, at an EVO of 60, 62, and 60° b BDC, respectively. The minimum value of PEP for WCO20, WCO30, and WCO100 was found to be 4.305 kW at 46° b BDC, 4.2704 kW at 48° b BDC, and 4.0872 kW at 46° b BDC, respectively. For diesel, the maximum PEP was recorded as 4.5089 kW, found at 64° b BDC. Among all the blends of WCO biodiesel, the PEP for WCO20 was found closest to diesel at 60° b BDC, which is about 3.972% lower than diesel.

In the second step, when the EVC was kept variable and the EVO was set at the optimum for the corresponding blends, the maximum values of PEP for WCO10, WCO20, WCO30, and WCO100 were found to be 4.3532 kW at 10° a TDC, 4.3422 kW at 10° a TDC, 4.3169 kW at 12° a TDC, and 4.1336 kW at 14° a TDC, whereas the minimum values of PEP were found to be 4.2832 kW at 20° a TDC, 4.2625 kW at 20° a TDC, 4.2723 kW at 6° a TDC, and 4.1025 kW at 6° a TDC, respectively. When all the blends of WCO biodiesel were compared, it was found that the PEP for WCO10 is closest to diesel at 10° a TDC, which is about 3.628% lower than diesel, as the maximum PEP for diesel is 4.5171 kW found at an EVC of 12° a TDC.

Specific fuel consumption

SFC is defined as the amount of fuel needed to generate one horsepower in one second.^33–35 It depends upon the fuel characteristics like viscosity, calorific value of fuel, and density used.³⁶ Due to their higher density, viscosity, and lower calorific value as compared to diesel, WCO biodiesel and its blends have higher SFC. When utilizing fuels with a lower calorific value, more gasoline is needed to provide the same amount of engine power. Additionally, because WCO biodiesel has a high density, more gasoline is pulled into the engine cylinder, which raises fuel consumption (Figure 4).³⁶

Optimum results were obtained at an EVO of 60° b BDC for WCO10, 60° b BDC for WCO20, 62° b BDC for WCO30, and 60° b BDC for WCO100.

The optimum value of EVC was obtained at 10° a TDC for WCO10, 10° a TDC for WCO20, 12° a TDC for WCO30, and 14° a TDC for WCO100.

Figure 4.

Variations in the SFC with different fuel blends at the exhaust valve timings (a) EVO, (b) EVC.

On comparing the values of SFC for WCO10 at different values of EVO, it was found that the max. and min. values of SFC are 0.258 and 0.25683 kg/kWh, which were found when the exhaust valve was opened at 46 and 60° b BDC. Similarly, the maximum value of SFC for WCO20, WCO30, and WCO100 was recorded as 0.2611, 0.26731, and 0.31295 kg/kWh, respectively, at an EVO of 46, 48, and 46° b BDC, respectively. The minimum value of SFC for WCO20, WCO30, and WCO100 was found to be 0.25965 kg/kWh at 60° b BDC, 0.26595 kg/kWh at 62° b BDC, and 0.3113 kg/kWh at 60° b BDC, respectively. For diesel, the minimum SFC was recorded as 0.24451 kg/kWh, found at 64° b BDC. Among all the blends of WCO biodiesel, the SFC for WCO10 was found closest to diesel at 60° b BDC, which is about 5.039% higher than diesel. In the second step, when the EVC was kept variable and the EVO was set at the optimum for the corresponding blends, the maximum values of SFC for WCO10, WCO20, WCO30, and WCO100 were found to be 0.25746 kg/kWh at 20° a TDC, 0.26344 kg/kWh at 20° a TDC, 0.26629 kg/kWh at 20° a TDC, and 0.31178 kg/kWh at 20° a TDC, whereas the minimum values of SFC were found to be 0.25122 kg/kWh at 16° a TDC, 0.25949 kg/kWh at 10° a TDC, 0.26508 kg/kWh at 10° a TDC, and 0.31018 kg/kWh at 14° a TDC, respectively. When all the blends of WCO biodiesel were compared, it was found that the SFC for WCO10 is closest to diesel at 16° a TDC, which is about 2.698% higher than diesel, as the minimum SFC for diesel is 0.24462 kg/kWh found at an EVC of 10° a TDC.

Indicated efficiency

The power generated by the engine before it is transferred to the piston determines the engine's reported efficiency. The ratio of energy in the stated power to input fuel energy is how indicated efficiency (IE) is mathematically defined. High IE means that the same amount of fuel energy is being used to generate high indicated power at the piston.³⁷ The IE of biodiesel and blends (except WCO10) is lower compared to diesel because of their low heating value.²⁸ IE of WCO10 is found similar to diesel (Figure 5).

Figure 5.

Variations in the IE with different fuel blends at the exhaust valve timings (a) EVO, (b) EVC.

On comparing the values of IE for WCO10 at different values of EVO, it was found that the max. and min. values of IE are 0.42538 and 0.42235, which were found when the exhaust valve was opened at 48 and 66° b BDC. Similarly, the maximum value of IE for WCO20, WCO30, and WCO100 was recorded as 0.42265, 0.42003, and 0.39502, respectively, at an EVO of 48, 46, and 46° b BDC, respectively. The minimum value of IE for WCO20, WCO30, and WCO100 was found to be 0.41981 at 66° b BDC, 0.41714 at 66° b BDC, and 0.39115 at 66° b BDC, respectively. For diesel, the maximum IE was recorded as 0.42509, found at 46° b BDC. Among all the blends of WCO biodiesel, the IE for WCO10 was found to be maximum at 48° b BDC, which is about 0.068% higher than diesel. Optimum results were obtained at an EVO of 60° b BDC for WCO10, 60° b BDC for WCO20, 62° b BDC for WCO30, and 60° b BDC for WCO100. In the second step, when the EVC was kept variable and the EVO was set at the optimum for the corresponding blends, the maximum values of IE for WCO10, WCO20, WCO30, and WCO100 were found to be 0.42337 at 10° a TDC, 0.41994 at 10° a TDC, 0.41808 at 14 and 16° a TDC, and 0.39272 at 12 and 14° a TDC, whereas the minimum values of IE were found to be 0.42288 at 20° a TDC, 0.41934 at 20° a TDC, 0.41729 at 6° a TDC, and 0.39221 at 6° a TDC, respectively. When all the blends of WCO biodiesel were compared, it was found that the IE for WCO10 is maximum at 10° a TDC, which is about 0.147% higher than diesel, as the maximum IE for diesel is 0.42275 found at an EVC of 12° a TDC.

The optimum value of EVC was obtained at 10° a TDC for WCO10, 10° a TDC for WCO20, 12° a TDC for WCO30, and 14° a TDC for WCO100.

Volumetric efficiency

The volume exchange rate, or VE, is the ratio of the airflow rate during the suction stroke to the piston's volume displacement rate. It serves as a gauge of the four-stroke engine cycle's overall efficacy. VE is influenced by variables such intake temperature and pressure, the ratio of exhaust to inlet manifold pressure, compression ratio, valve shape, and speed.^38,39 The VE, which limits the amount of fuel that can be burned effectively, determines the amount of air injected into the combustion chamber. More fuel is poured into the engine cylinder since biodiesel and its mixes have a low energy content. Consequently, when the mix ratio increases, the VE of biodiesel is higher than diesel (Figure 6).⁴⁰

Figure 6.

Variations in the VE with different fuel blends at the exhaust valve timings (a) EVO, (b) EVC.

On comparing the values of VE for WCO10 at different values of EVO, it was found that the maximum value of VE is 0.94673, found at an EVO of 48 and 50° b BDC and minimum value is 0.94664, which was found when the exhaust valve was opened at 46° b BDC. Similarly, the maximum value of VE for WCO20, WCO30, and WCO100 was recorded as 0.94882, 0.94877, and 0.95057, respectively, at an EVO of 48, 46, and 48° b BDC, respectively. The minimum value of VE for WCO20, WCO30, and WCO100 was found to be 0.94793 at 66° b BDC, 0.94785 at 66° b BDC, and 0.95004 at 46° b BDC, respectively. For diesel, the maximum VE was recorded as 0.94839, found at 54° b BDC. Among all the blends of WCO biodiesel, the VE for WCO100 was found to be maximum at 48° b BDC, which is about 0.23% higher than diesel.

Optimum results were obtained at an EVO of 60° b BDC for WCO10, 60° b BDC for WCO20, 62° b BDC for WCO30, and 60° b BDC for WCO100.

In the second step, when the EVC was kept variable and the EVO was set at the optimum for the corresponding blends, the maximum values of VE for WCO10, WCO20, WCO30, and WCO100 were found to be 0.95074 at 12° a TDC, 0.95057 at 10° a TDC, 0.95131 at 14° a TDC, and 0.95301 at 12° a TDC, whereas the minimum values of VE were found to be 0.94497 at 6° a TDC, 0.94521 at 6° a TDC, 0.94552 at 6° a TDC, and 0.94811 at 6° a TDC, respectively. When all the blends of WCO biodiesel were compared, it was found that the VE for WCO100 is highest at 12° a TDC, which is about 0.3% higher than diesel, as the maximum VE for diesel is 0.95016 found at an EVC of 14° a TDC.

The optimum value of EVC was obtained at 10° a TDC for WCO10, 10° a TDC for WCO20, 12° a TDC for WCO30, and 14° a TDC for WCO100.

Combustion characteristics

Ignition delay

Ignition delay (ID) is the amount of time between the start of fuel injection timing and the onset of fuel ignition as determined by the angle created by the crank as it rotates.⁴¹ This delay is divided into a physical delay caused by the atomization and vaporization of the fuel-air combination and a chemical delay caused by pre-combustion processes, these two processes occur simultaneously instead of overlapping.⁴² Biodiesel and its mixes were shown to have shorter IDs than diesel. This could be because biodiesel has a high cetane rating. The gasoline may auto-ignite more rapidly with a greater cetane number, which reduces the fuel's ID.¹⁸ Engine thermal efficiency, air-fuel ratio, and maximum heat release rate are all impacted by ID (Figure 7).⁴²

Figure 7.

Variations in the IDP with different fuel blends at the exhaust valve timings (a) EVO, (b) EVC.

On comparing the values of ID for WCO10 at different values of EVO, it was found that the max. and min. values of ID are 14.274 and 14.236°, which were found when the exhaust valve was opened at 48 and 66° b BDC. Similarly, the maximum value of ID for WCO20, WCO30, and WCO100 was recorded as 12.837, 11.582, and 4.0506°, respectively, at an EVO of 52, 54, and 46° b BDC, respectively. The minimum value of ID for WCO20, WCO30, and WCO100 was found to be 12.799° at 66° b BDC, 11.499° at 46° b BDC, and 4.0123° at 48° b BDC, respectively. For diesel, the max. and min. ID were recorded to be 14.432 and 14.415°, found at 54 and 56° b BDC respectively. Optimum results were obtained at an EVO of 60° b BDC for WCO10, 60° b BDC for WCO20, 62° b BDC for WCO30, and 60° b BDC for WCO100.In the second step, when the EVC was kept variable and the EVO was set at the optimum for the corresponding blends, the maximum values of ID for WCO10, WCO20, WCO30, and WCO100 were found to be 14.255° at 10° a TDC, 12.84° at 12° a TDC, 11.54° at 14° a TDC, and 4.0368° at 12° a TDC, whereas the minimum values of ID were found to be 13.988° at 6° a TDC, 12.59° at 6° a TDC, 11.288° at 6° a TDC, and 3.9307° at 6° a TDC, respectively. The maximum ID for diesel is 14.398° found at the EVC of 12 and 14° a TDC whereas minimum ID is 14.149° found at 6° a TDC.The optimum value of EVC was obtained at 10° a TDC for WCO10, 10° a TDC for WCO20, 12° a TDC for WCO30, and 14° a TDC for WCO100.

Maximum cylinder pressure

The ID duration affects the MCP of the engine. Due to their shorter IDs, biodiesel and its mixes were shown to have lower MCPs than diesel.^43,44 The other factors responsible for the lower peak cylinder pressure while using biodiesel are low atomization process and higher viscosity of biodiesel.⁴⁵ On comparing the values of MCP for WCO10 at different values of EVO, it was found that the maximum value of MCP is 90.254 bar at 46 and 48° b BDC and minimum value is 90.181 bar, which was found when the exhaust valve was opened at 66° b BDC. Similarly, the maximum value of MCP for WCO20, WCO30, and WCO100 was recorded as 87.946, 86.22, and 74.644 bar, respectively, at an EVO of 52, 54, and 60° b BDC, respectively. The minimum value of MCP for WCO20, WCO30, and WCO100 was found to be 87.874 bar at 66° b BDC, 86.097 bar at 50° b BDC, and 74.6 bar at 48° b BDC, respectively. For diesel, the maximum MCP was recorded as 90.65 bar, found at 52° b BDC. Among all the blends of WCO biodiesel, the MCP for WCO10 was found closest to Diesel at 46 and 48° b BDC, which is about 0.437% lower than Diesel. Optimum results were obtained at an EVO of 60° b BDC for WCO10, 60° b BDC for WCO20, 62° b BDC for WCO30, and 60° b BDC for WCO100.In the second step, when the EVC was kept variable and the EVO was set at the optimum for the corresponding blends, the maximum values of MCP for WCO10, WCO20, WCO30, and WCO100 were found to be 90.454 bar at 10° a TDC, 88.168 bar at 10° a TDC, 86.398 bar at 14° a TDC, and 74.803 bar at 12° a TDC, whereas the minimum values of MCP were found to be 89.809 bar at 6° a TDC, 87.599 bar at 6° a TDC, 85.846 bar at 6° a TDC, and 74.609 bar at 6° a TDC, respectively. When all the blends of WCO biodiesel were compared, it was found that the MCP for WCO10 is closest to diesel at 10° a TDC, which is about 0.507% lower than diesel, as the maximum MCP for diesel is 90.915 bar found at an EVC of 12° a TDC (Figure 8).

Figure 8.

Variations in the MCP with different fuel blends at the exhaust valve timings (a) EVO, (b) EVC.

The optimum value of EVC was obtained at 10° a TDC for WCO10, 10° a TDC for WCO20, 12° a TDC for WCO30, and 14° a TDC for WCO100.

Maximum cylinder temperature

The temperature of cylinder raises with the rise in flame temperature. It significantly affects the engine's banging and emissions. When the maximum cylinder temperature is higher, NOX emissions are greater (MCT).⁴⁶ Due to their increased oxygen content and lower NOX emission, biodiesel and its blends have decreased MCT. Utilizing biodiesel and its mixes at low temperatures has the benefit of reducing heat loss via the engine cylinder.^47,48On comparing the values of MCT for WCO10 at different values of EVO, it was found that the max. and min. values of MCT are 1770.6 and 1767.3 K, which were found when the exhaust valve was opened at 46 and 66° b BDC. Similarly, the maximum value of MCT for WCO20, WCO30, and WCO100 was recorded as 1752.2, 1731.4, and 1558.5 K, respectively, at an EVO of 46, 48, and 46° b BDC, respectively. The minimum value of MCT for WCO20, WCO30, and WCO100 was found to be 1749 K at 66° b BDC, 1729.9 K at 66° b BDC, and 1558 K at 48° b BDC, respectively. For diesel, the maximum MCT was recorded as 1786.6 K, found at 66° b BDC. Among all the blends of WCO biodiesel, the MCT for WCO10 was found closest to diesel at 46° b BDC, which is about 0.896% lower than diesel. Optimum results were obtained at an EVO of 60° b BDC for WCO10, 60° b BDC for WCO20, 62° b BDC for WCO30, and 60° b BDC for WCO100.In the second step, when the EVC was kept variable and the EVO was set at the optimum for the corresponding blends, the maximum values of MCT for WCO10, WCO20, WCO30, and WCO100 were found to be 1768.3 K at 10, 12 and 14° a TDC, 1752.5 K at 12° a TDC, 1731.3 K at 10° a TDC, and 1558.5 K TDC, 1746.2 K at 20° a TDC, 1728.5 K at 6° a TDC, and 1557.6 K at 6° a TDC, respectively. When all the blends of WCO biodiesel were compared, it was found that the MCT for WCO10 is closest to diesel at 10, 12 and 14° a TDC, which is about 1.069% lower than diesel, as the maximum MCT for diesel is 1787.4 K found at an EVC of 12° a TDC (Figure 9).

Figure 9.

Variations in the MCT with different fuel blends at the exhaust valve timings (a) EVO, (b) EVC.

The optimum value of EVC was obtained at 10° a TDC for WCO10, 10° a TDC for WCO20, 12° a TDC for WCO30, and 14° a TDC for WCO100 (Figure 10).

Figure 10.

Variations in the average exhaust manifold gas temperature with different fuel blends at the exhaust valve timings (a) EVO, (b) EVC.

Exhaust gas temperature

Exhaust gas temperature (EGT) is the temperature of the gases that are expelled into the atmosphere at the conclusion of the combustion process inside the engine cylinder. It is a significant element that contributes to the creation of pollutants during the exhaust process.^49,50 The oxygen content of the fuel affects the EGT. Despite having a lower heating value than diesel, early full combustion occurs in biodiesel and its mixes because of the increased oxygen concentration.⁵¹On comparing the values of EGT for WCO10 at different values of EVO, it was found that the max. and min. values of EGT are 611.84 and 609.65 K, which were found when the exhaust valve was opened at 46 and 50° b BDC. Similarly, the maximum value of EGT for WCO20, WCO30, and WCO100 was recorded as 615.62, 620.72, and 664.62 K, respectively, at an EVO of 62, 66, and 46° b BDC, respectively. The minimum value of EGT for WCO20, WCO30, and WCO100 was found to be 613.35 K at 52° b BDC, 618.03 K at 46° b BDC, and 658.69 K at 66° b BDC, respectively. For diesel, the minimum EGT was recorded as 618.34 K, found at 52° b BDC. Among all the blends of WCO biodiesel, the EGT for WCO10 was found to be minimum at 50° b BDC, which is about 1.405% lower than diesel. Optimum results were obtained at an EVO of 60° b BDC for WCO10, 60° b BDC for WCO20, 62° b BDC for WCO30, and 60° b BDC for WCO100. In the second step, when the EVC was kept variable and the EVO was set at the optimum for the corresponding blends, the maximum values of EGT for WCO10, WCO20, WCO30, and WCO100 were found to be 611.22 K at 20° a TDC, 618.04 K at 20° a TDC, 621.49 K at 6° a TDC, and 660.98 K at 20° a TDC, whereas the minimum values of EGT were found to be 609.23 K at 16° a TDC, 616.29 K at 10° a TDC, 619.18 K at 16° a TDC, and 660.11 K at 10 and 12° a TDC, respectively. When all the blends of WCO biodiesel were compared, it was found that the EGT for WCO10 is lowest at 16° a TDC, which is about 1.716% lower than diesel, as the minimum EGT for diesel is 619.87 K found at an EVC of 16° a TDC.

The optimum value of EVC was obtained at 10° a TDC for WCO10, 10° a TDC for WCO20, 12° a TDC for WCO30, and 14° a TDC for WCO100 (Figure 11).

Figure 11.

Variations in the specific CO₂ emission with different fuels blends at the exhaust valve timings (a) EVO, (b) EVC.

Emission characteristics

CO₂ emission

During combustion, atmospheric oxygen reacts with the carbon contents of fuel to produce CO₂. In diesel fuel, due to low oxygen contents CO₂ emissions reduced because of incomplete fuel combustion, which results in increase of CO emission. With increase in cetane number of fuels, rate of complete combustion increase whereas incomplete combustion decreases. WCO biodiesel and its blend have high cetane number than diesel. The formation mechanism of CO₂ emission is opposite to CO emission. Therefore, biodiesel and blends have higher CO₂ emissions than diesel due to higher oxygen content.⁴³ On comparing the values of CO₂ for WCO10 at different values of EVO, it was found that the max. and min. values of CO₂ are 822.05 and 818.34 g/KWh, which were found when the exhaust valve was opened at 46 and 60° b BDC. Similarly, the maximum value of CO₂ for WCO20, WCO30, and WCO100 was recorded as 821.98, 831.43, and 890.18 g/kWh, respectively, at an EVO of 46, 48, and 46° b BDC, respectively. The minimum value of CO₂ for WCO20, WCO30, and WCO100 was found to be 817.42 g/KWh at 60° b BDC, 827.2 g/KWh at 62° b BDC, and 885.46 g/KWh at 60° b BDC, respectively. For diesel, the minimum CO₂ was recorded as 787.87 g/KWh, found at 64° b BDC. Among all the blends of WCO biodiesel, the CO₂ for WCO20 was found closest to diesel at 60° b BDC, which is about 3.75% higher than diesel. Optimum results were obtained at an EVO of 60° b BDC for WCO10, 60° b BDC for WCO20, 62° b BDC for WCO30, and 60° b BDC for WCO100.In the second step, when the EVC was kept variable and the EVO was set at the optimum for the corresponding blends, the maximum values of CO₂ for WCO10, WCO20, WCO30, and WCO100 were found to be 823.54 g/KWh at 20° a TDC, 829.34 g/KWh at 20° a TDC, 828.27 g/KWh at 20° a TDC, and 886.84 g/KWh at 20° a TDC, whereas the minimum values of CO₂ were found to be 812.73 g/KWh at 10° a TDC, 816.9 g/KWh at 10° a TDC, 824.49 g/KWh at 10° a TDC, and 882.28 g/KWh at 14° a TDC, respectively. When all the blends of WCO biodiesel were compared, it was found that the CO₂ for WCO10 is closest to diesel at 10° a TDC, which is about 3.109% higher than diesel, as the minimum CO2 for diesel is 788.22 g/KWh found at an EVC of 10° a TDC. The optimum value of EVC was obtained at 10° a TDC for WCO10, 10° a TDC for WCO20, 12° a TDC for WCO30, and 14° a TDC for WCO100.

SO₂ emission

Sulfur emissions are released from the engine because of presence of sulfur in fuel. This sulfur content combines with oxygen to form sulfur dioxide (SO₂). Further, the oxygen available in the exhaust can react with this SO₂ to form sulfur trioxide (SO₃). SO₂ and SO₃ are highly toxic as they react with water vapour in the atmosphere to form sulfuric acid which is responsible for acid rain. SO₂ emissions affect the air quality, damage the growth of plants and trees, cause irritation in eyes, reduce visibility, and also responsible for respiratory diseases.⁵² Biodiesel and its blends have lower SO₂ emissions because of their lower sulfur content compared to diesel (Figure 12).

Figure 12.

Variations in the specific SO₂ emission with different fuel blends at the exhaust valve timings (a) EVO, (b) EVC.

On comparing the values of SO₂ for WCO10 at different values of EVO, it was found that the max. and min. values of SO₂ are 0.0098 and 0.00976 g/KWh, which were found when the exhaust valve was opened at 46 and 60° b BDC. Similarly, the maximum value of SO₂ for WCO20, WCO30, and WCO100 was recorded as 0.0094, 0.00909, and 0.00626 g/KWh, respectively, at an EVO of 46, 48, and 46° b BDC, respectively. The minimum value of SO₂ for WCO20, WCO30, and WCO100 was found to be 0.00935 g/KWh at 60° b BDC, 0.00904 g/KWh at 62° b BDC, and 0.00623 g/KWh at 60° b BDC, respectively. For diesel, the minimum SO₂ was recorded as 0.00978 g/KWh, found at 64° b BDC. Among all the blends of WCO biodiesel, the SO₂ for WCO100 at 60° b BDC was found to be minimum and 36.298% lower than diesel. Optimum results were obtained at an EVO of 60° b BDC for WCO10, 60° b BDC for WCO20, 62° b BDC for WCO30, and 60° b BDC for WCO100.In the second step, when the EVC was kept variable and the EVO was set at the optimum for the corresponding blends, the maximum values of SO₂ for WCO10, WCO20, WCO30, and WCO100 were found to be 0.00982 g/KWh at 20° a TDC, 0.00948 g/KWh at 20° a TDC, 0.00905 g/KWh at 6 and 20° a TDC, and 0.00624 g/KWh at 20° a TDC, whereas the minimum values of SO₂ were found to be 0.00969 g/KWh at 10° a TDC, 0.00934 g/KWh at 10° a TDC, 0.00901 g/KWh at 10 and 12° a TDC, and 0.0062 g/KWh at 10, 12 and 14° a TDC, respectively. When all the blends of WCO biodiesel were compared, it was found that the SO₂ for WCO100 is lowest at 12 and 14° a TDC, which is about 36.605% lower than diesel, as the minimum SO₂ for diesel is 0.00978 g/KWh found at an EVC of 10° a TDC. The optimum value of EVC was obtained at 10° a TDC for WCO10, 10° a TDC for WCO20, 12° a TDC for WCO30, and 14° a TDC for WCO100.

No_x emission

In order to ignite the gasoline inside the cylinder, an IC engine requires oxygen. This oxygen is acquired from atmospheric air that has 21% oxygen by volume. However, nitrogen (79% of this air) comprises the majority of it, and nitrogen interacts with oxygen at extreme pressures and temperatures to create NOX emissions in a procedure termed as the Zeldovich mechanism.^53–55 On comparing the NO_X values for WCO10 at different values of EVO, it was found that the max. and min. values of NO_X are 1374.9 and 1358.4 ppm, which were found when the exhaust valve was opened at 66 and 46° b BDC (Figure 13).

Figure 13.

Variations in the NOx with different fuel blends at the exhaust valve timings (a) EVO, (b) EVC.

Similarly, the maximum value of NO_X for WCO20, WCO30, and WCO100 was recorded as 1486.7, 1541.8, and 1552.6 ppm, respectively, at an EVO of 48, 46, and 48° b BDC, respectively. The minimum value of NO_X for WCO20, WCO30, and WCO100 was found to be 1479.6 ppm at 62° b BDC, 1528.6 ppm at 62° b BDC, and 1541.9 ppm at 66° b BDC, respectively. For diesel, the minimum NO_X was recorded as 1602.4 ppm, found at 66° b BDC. Among all the blends of WCO biodiesel, the NO_X for WCO10 was found to be minimum at 46° b BDC, which is about 15.227% lower than Diesel. Optimum results were obtained at an EVO of 60° b BDC for WCO10, 60° b BDC for WCO20, 62° b BDC for WCO30, and 60° b BDC for WCO100. In the second step, when the EVC was kept variable and the EVO was set at the optimum for the corresponding blends, the maximum values of NO_X for WCO10, WCO20, WCO30, and WCO100 were found to be 1387.1 ppm at 10° a TDC, 1485.7 ppm at 10° a TDC, 1541.7 ppm at 12° a TDC, and 1554.3 ppm at 12° a TDC, whereas the minimum values of NO_X were found to be 1346.6 ppm at 6° a TDC, 1434.6 ppm at 20° a TDC, 1510.2 ppm at 6° a TDC, and 1532 ppm at 6° a TDC, respectively. When all the blends of WCO biodiesel were compared, it was found that the NO_X for WCO10 is found to be minimum at 6° a TDC, which is about 15.350% lower than diesel, as the minimum NO_X for diesel is 1590.8 ppm found at an EVC of 6° a TDC.

The optimum value of EVC was obtained at 10° a TDC for WCO10, 10° a TDC for WCO20, 12° a TDC for WCO30, and 14° a TDC for WCO100.

Bosch smoke number

Bosch smoke number (BSN) is a symbol for the smoke properties of exhaust gases. Incomplete burning of hydrocarbons, incorrect combustion, and a lack of oxygen all contribute to the smoke production.⁵⁶ During combustion, the hydrogen molecules in the fuel quickly react with the oxygen molecules which causes redundancy of oxygen for the burning of carbon. The unburnt carbon is released as smoke.⁵⁷ Reason behind this is the heterogeneous mixture of air and fuel inside the combustion chamber. The smoke emission also depends upon swirl motion, combustion temperature, fuel viscosity, flame velocity, and engine load.⁵⁸ The BSN of WCO10 was found similar to diesel and BSN of WCO20 and WCO30 was slightly higher than diesel. However, BSN for WCO100 is higher compared to diesel. It might be a result of the substance's high viscosity, which alters the spray pattern and contributes to the soot concentration (Figure 14).⁵⁹

Figure 14.

Variations in the BSN with different fuel blends at the exhaust valve timings (a) EVO, (b) EVC.

On comparing the values of BSN for WCO10 at different values of EVO, it seemed that the max. and min. values of BSN are 1.9529 and 1.9205, which were found when the exhaust valve was opened at 46 and 48° b BDC. Similarly, the maximum value of BSN for WCO20 and WCO30 was recorded as 2.1463, and 2.3189, respectively, at an EVO of 62 and 66° b BDC, respectively. The minimum value of BSN for WCO20 and WCO30 was found to be 2.1282 at 48° b BDC and 2.3091 at 48° b BDC, respectively. The maximum value of BSN for WCO100 was found to be 3.6531 at the EVO of 62 and 66° b BDC and the minimum value is 3.6521 found at the EVO of 46 and 54° b BDC. For diesel, the minimum BSN was recorded as 1.9485, found at 52° b BDC. Among all the blends of WCO biodiesel, the BSN for WCO10 was found to be minimum at 48° b BDC, which is about 1.437% lower than diesel. Optimum results were obtained at an EVO of 60° b BDC for WCO10, 60° b BDC for WCO20, 62° b BDC for WCO30, and 60° b BDC for WCO100. In the second step, when the EVC was kept variable and the EVO was set at the optimum for the corresponding blends, the maximum values of BSN for WCO10, WCO20, WCO30, and WCO100 were found to be 1.945 at 6° a TDC, 2.1552 at 6° a TDC, 2.3376 at 6° a TDC, and 3.658 at 6° a TDC, whereas the minimum values of BSN were found to be 1.9149 at 10° a TDC, 2.1201 at 10° a TDC, 2.3062 at 12° a TDC, and 3.6498 at 12° a TDC, respectively. When all the blends of WCO biodiesel were compared, it was found that the BSN for WCO10 is lowest at 10° a TDC, which is about 1.365% lower than diesel, as the minimum BSN for diesel is 1.9414 found at an EVC of 12° a TDC. The optimum value of EVC was obtained at 10° a TDC for WCO10, 10° a TDC for WCO20, 12° a TDC for WCO30, and 14° a TDC for WCO100.

Particulate matter

Whenever fuel and atmospheric air interact, particulate matter (PM) is created. They are a combustion by-product. In a diesel engine, the majority of the soot is burnt within the cylinder, while a tiny proportion is left over and expelled through the exhaust. Exhaust gases cool, nucleate, condense, and generate tiny particles referred as PM or aerosols during the process of dispersion in the exhaust. They usually comprise silica, salt, potassium, iron, and other materials.⁶⁰ The dry spots (DS) and soluble organic components are often part of the PM emissions (SOF).⁶¹ Because biodiesels possess more oxygen than diesel, they release lesser DS pollutants. On the other hand, biodiesel has higher SOF emissions than diesel owing to its high viscosity and surface tension factor. At all valve timings, biodiesel has higher overall PM emissions than diesel (Figure 15).⁶²

Figure 15.

Variations in the PM with different fuel blends at the exhaust valve timings (a) EVO, (b) EVC.

On comparing the values of PM for WCO10 at different values of EVO, it was found that the maximum and minimum values of PM are 0.52755 and 0.51564 g/KWh, which were found when the exhaust valve was opened at 46 and 54° b BDC. Similarly, the maximum value of PM for WCO20, WCO30, and WCO100 was recorded as 0.59936, 0.6724, and 1.3559 g/KWh, respectively, at an EVO of 46, 50, and 46° b BDC, respectively. The minimum value of PM for WCO20, WCO30, and WCO100 was found to be 0.59138 g/kWh at 60° b BDC, 0.66601 g/kWh at 62° b BDC, and 1.3488 g/kWh at 60° b BDC, respectively. For diesel, the minimum PM was recorded as 0.50341 g/kWh, found at 58° b BDC. Among all the blends of WCO biodiesel, the PM for WCO10 was found closest to diesel at 54° b BDC, which is about 2.429% higher than diesel.

Optimum results were obtained at an EVO of 60° b BDC for WCO10, 60° b BDC for WCO20, 62° b BDC for WCO30, and 60° b BDC for WCO100. In the second step, when the EVC was kept variable and the EVO was set at the optimum for the corresponding blends, the maximum values of PM for WCO10, WCO20, WCO30, and WCO100 were found to be 0.52457 g/KWh at 6° a TDC, 0.60752 g/KWh at 6° a TDC, 0.6775 g/KWh at 6° a TDC, and 1.3566 g/KWh at 6° a TDC, whereas the minimum values of PM were found to be 0.51075 g/KWh at 10° a TDC, 0.58723 g/KWh at 10° a TDC, 0.66335 g/KWh at 12° a TDC, and 1.3439 g/KWh at 12° a TDC, respectively. When all the blends of WCO biodiesel were compared, it was found that the PM for WCO10 is closest to diesel at 10° a TDC, which is about 2.001% higher than diesel, as the minimum PM for diesel is 0.50073 g/KWh found at an EVC of 12° a TDC. The optimum value of EVC was obtained at 10° a TDC for WCO10, 10° a TDC for WCO20, 12° a TDC for WCO30, and 14° a TDC for WCO100.

Conclusion

The opening of the exhaust valve has a significant impact on the performance parameters of the diesel engine. Different fuels and blends exhibit distinct characteristics at various values of EVO and EVC. In this study, the range of EVO varies from 42 to 60° b BDC for all biofuel blend cases. Among them, WCO20 demonstrates optimized values for most performance parameters at a specific EVO, except for one parameter. The following are some of the performance characteristics observed:

Brake thermal efficiency, BT, and PEP were observed to be higher with pure diesel at different EVO and EVC values.

Higher SFC was observed with WCO100 at different EVO and EVC.

Indicated thermal efficiency of pure diesel was almost equal to WCO10 at different EVO. Volumetric efficiency was the highest among all the fuels in this study at different EVO and EVC.

ID was maximum with WCO10 and WCO100 at different EVO and EVC.

The maximum cylinder pressure was observed with pure diesel and WCO10 at different EVO and EVC.

The lowest exhaust manifold temperature was observed with WCO10 at different EVO and EVC. The lowest cylinder temperature was observed with WCO100 at different EVO and EVC.

The lowest average temperature of the exhaust gas was observed with WCO10 at different EVO and EVC.

Similarly, the values of EVO and EVC also affect the combustion characteristics, which are as follows:

The lowest CO₂ emission was observed with pure diesel at different EVO and EVC.

The lowest SO₂ emission was observed with WCO100 at different EVO and EVC. WCO10 generated the highest SO₂, equal to pure diesel, at different EVO.

The lowest NOx emission was observed with WCO10 at different EVO and EVC.

The lowest BSN was observed with WCO10 at different EVO and EVC.

The lowest PM was observed with WCO10 and pure diesel at different EVO and EVC.

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the King Saud University (grant number RSP2023R6).

ORCID iDs

Santosh Patel

Mahaboob Patel

Nomenclature

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Impact of variable exhaust valve timing on diesel engine characteristics fueled with waste cooking oil biofuel blends: A numerical analysis

Abstract

Keywords

Introduction

Proposed methodology

Engine specifications

Experimental procedure

Numerical method

Conservation of mass

Energy conservation

Brake mean effective pressure

Specific fuel consumption

Brake torque

Indicated efficiency

Mechanical efficiency

Volumetric efficiency

Heat transfer factor in cooling system

Nox formation

Soot formation

Sox formation

Results and discussions

Performance characteristics

Brake mean effective pressure

Brake torque

Piston engine power

Specific fuel consumption

Indicated efficiency

Volumetric efficiency

Combustion characteristics

Ignition delay

Maximum cylinder pressure

Maximum cylinder temperature

Exhaust gas temperature

Emission characteristics

CO2 emission

SO2 emission

Nox emission

Bosch smoke number

Particulate matter

Conclusion

Footnotes

Declaration of conflicting interests

Funding

ORCID iDs

Nomenclature

References

No_x formation

So_x formation

CO₂ emission

SO₂ emission

No_x emission