Influence of fuel system variations on performance and emission characteristics of combined air-wall-guided mode modified GDI engine with alcoholic fuels and exhaust gas recirculation

GDI engines commercially existed with spray-guided mode where the fuel injector placed almost vertically and sprayed fuel is occupied throughout the volume of combustion chamber. With the advanced emission norms, NOx and soot emissions control is the major task along with lower fuel consumption. To achieve the advanced emission norms, further modifications are required before or during combustion. Combined air-wall guided mode combustion chamber modification is the advanced stage required for further improvement in mixing and superior combustion. Combined air-wall guided mode involved piston crown shape modification so that the modified shape must impart turbulence effects and divert the fuel/mixture flow towards the spark plug tip to initiate the combustion process. In this study, the combined air-wall-guided mode gasoline direct injection engine was tested with gasoline blends using ethanol, methanol and N-butanol at 20, 35 and 50% proportions under specific fixed conditions: 1500 rpm speed, 10% EGR and FIP of 150 bars with three split injections at 320°, 220° and 100° before TDC at different injection durations. Tests were conducted over these gasoline blend proportions for engine performance and emission characteristics and achieved the beneficial results with E20 gasoline blend over the entire applied torque values. E20 blend develops maximum IMEP of 8.3% at 50% blend proportion and as significant increment of 7.4% at 20% of blend proportion. E20 blended fuel shown a maximum decrement of SFC up to 7.2%. Significant reduction of CO emission up to 11.3% for E20 blend and maximum reduction of 12% for E50 blend. HC emissions were decreased significantly up to 14% for E20 blend and it reached maximum reduction of 20.3% for E50 blend. NOx emissions showed lower concentrations for E20 blend with a decrement of 13.3% and higher for B35 blend. Soot particle emissions were decreased significantly up to 27% for E20 blend and it reached maximum reduction of 33.34% for E50 blend.


Introduction
Spark ignition (SI) engine uses petrol/gasoline as fuel with high latent heat of vaporization whereas compression ignition (CI) engine uses diesel as fuel with low latent heat of vaporization. SI engines produces less concentrations of NOx and Soot particle emissions compared to CI engines. GDI engines operate at high fuel injection pressure and the highly pressurized fuel injected directly into an engine cylinder. GDI engines avoid the possibility of erosion of inlet valve neck portion, reduce the chances of wall wetting/fuel impingement, improve fuel economy with precise control of fuel, reduce an engine out emissions, etc. Because of lean burn operation and direct fuel injection, NOx and soot particle emissions reduction is the challenging task in GDI engines. Dual fuel injection system was incorporated to reduce the chances of knocking and NOx emission formation in GDI engines. The fuel injection pressure was optimized between 20 and 150 bar towards better mixture formation and superior combustion.
The gasoline blends with iso-propanol and iso-butanol from 0 to 30% by volume were tested at 20 and 40 bar injection pressures and the results showed that at low temperature, the blends provide low carbon intensity because of its knocking suppress characteristics (Scott et al. 2021). The emission factors of 5 vehicles tested on chassis dynamometer shows that decrease remarkably with emission standard from 11.7 to 6 μg per km (Zheng et al. 2018). To boost up an engine combustion performance at lower in-cylinder temperature, the thermo-chemistry kinetic models were developed with iso-methyl or isobutyl alcohols with gasoline blends for enriching spark ignition .
N-butanol has higher calorific value than other alcoholic fuel used; its blend result shows comparatively higher indicated mean effective pressure and thermal efficiency (Gorbatenko et al. 2019). 2,5 Di-methyl furan has relatively higher octane number than gasoline fuel; other than ethanol, DMF's energy density was similar to gasoline fuel. Because of higher calorific value and density, DMF blend test results show more concentration of NOx and soot particle emissions in an engine exhaust (Xu and Wang 2016;Hoang et al. 2021).
Ethanol gasoline blends were tested on a two wheeler engine at speed ranges 200, 400, 600, 800 and 1000 rpm; results show that E10 blend at 800 rpm, SFC was comparatively low, 26% gain in brake thermal efficiency at 1000 rpm, less soot particle emissions; E50 blend shows less NOx emissions; E30 blend shows comparatively low CO emissions (Sameeth Raj et al. 2019). EGR fitted GDI engine was tested with hydrogen fuel from exhaust gas fuel reforming with side mounted solenoid fuel injector; results indicated that decrease in PN level and soot mass emissions (Fennell et al. 2014). Ethanol proportions at 10, 20 and 30% by volume with gasoline was tested and observed that CO and NOx emissions were reduced than gasoline and a remarkable reduction in HC emission than oxygen free gasoline (Iodice et al. 2017). An increase in anhydrous ethanol-gasoline blend results in significant drop of CO and THC emission concentrations (Ribeiro et al. 2018). The urban environmental impact of gasolineethanol blended fuels in a passenger vehicle engine with different speeds was evaluated (Duarte et al. 2021). Ethanol gasoline blends at proportions of 10, 20 and 100% were tested on both laboratories with chassis dynamometer and on on-road conditions, which observed 2% reduction in the power output and torque, also in CO and NOx emissions with E20 blend fuel. HC and CO 2 emissions were slightly increased with E20 blend (Tibaquira et al. 2018).
N-Heptane and Iso-octane gasoline binary blends at different octane numbers were tested; the ignition timings and laminar flame speeds were perfectly projected over a range of engine operating conditions (Lapointe et al. 2018). Twelve and 20% N-butanol gasoline blends were tested for performance and emissions of SI engine and it was observed that HC and CO emissions were relatively lower than petrol; BSFC is found to be higher than gasoline due to its lower calorific value (Abdulazeez et al. 2018).
Methanol-gasoline blends with 5, 10 and 15% proportions were tested repeatedly and noted that M10 blend has less BSFC compared with other blend proportions. M15 showed comparatively lower emissions than other blend fuels and also it has higher A/F ratio (Danaiah et al. 2013). Even though DMF has an option to serve as a SI engine fuel blend without any modifications, it fails to satisfy the existing emission norms, majorly NOx and soot particle emissions (Shukla et al. 2014).
Methanol gasoline blends at 5, 10, 20, 30 and 50% proportions were tested for engine performance and emissions; the results showed that torque and power increases, BSFC also increases with the increase of concentrations of methanol in the blend (Iliev 2020). Methanol-gasoline blends were burned in a small volume, which results in heat released in shorter time; higher pressure exhaust gas was developed closer to TDC; increased proportions of methanol results in increased brake thermal efficiency. M85 blended fuel results in reduced of HC, CO and PM emissions (Yanju et al. 2008). N-Heptane methanol blended fuels were tested towards the burning characteristics and observed that the azeotropism between methanol and heptane, which lowers the burning quality compared to gasoline fuel (Gao et al. 2021).
For implementing the advanced injection parameters with effective reduced emissions and superior combustion performance. Kirloskar make, single cylinder, diesel engine gives more benefit on operating cost. SCO is the cost benefit fuel 1 3 with high levels of harmful emissions and can be improved with dual fuel mode of gaseous fuels (Karthic et al. 2020). The use of methyl-ester rapeseed oil biodiesel was recommended to reduce the total mass of particulate and metal emissions from diesel engines (Coufalik et al. 2019).
The chambered turbo type muffler with methanol gasoline fuel blends was tested towards better fuel property, performance and emission characteristics (Mishra et al. 2018). On road tests were conducted to characterize the harmful gas emissions from petrol and diesel engines, the concentrations of CO and NOx decreased comparatively. With lower rate of EGR with modification on the intake manifold for using the engine with bio-diesel blends which results in high NOx emissions (Khan 2020).
Synthetic oil was mixed up with ethanol gasoline blends and tested for its effects towards its lubrication properties and observed that it decreases the viscosity of the engine oil an increases the acidic rating compared to gasoline fuel, also degradation of oil. E10 blend has very less impact on frictional wear properties than other blends (Khuong et al. 2017).
Gasoline-N-butanol blends show decrement in SFC and CO 2 emissions at steady state; increase of N-butanol proportions in the blend results in reduced HC, CO, NO and soot emissions. Ethanol gasoline fuel blends shows significant reduction of HC, PN and NOx than other alcohol blends (Liu et al. 2019).
The split fuel injection timings with injection durations and the piston crown surfaces were modified towards proper mixing, superior combustion and emissions control, especially NOx and soot particle emissions (N Shivakumar et al. 2020;Kumar 2020). NOx emissions were reduced to more than 90% using HCCI combustion technology with natural gas (Verma et al. 2021). The modified combustion chamber geometry (spray-guided, wall-guided and air-guided) GDI engines were tested for their fuel economy and emission characteristics at the specified conditions: 1500 rpm rated speed, 10% EGR, compression ratio of 10:1, the fuel injection pressures at 100, 125, 150 and 175 bars with an optimized three split injections at different total injection durations and optimized ignition timings. The wall-guided combustion chamber geometry GDI engine showed better performance on fuel economy and emissions control than other two combustion chamber geometry modes (Nagareddy et al. 2022;Tamilvanan et al. 2022).
The main objective of this work is to obtain the optimal results towards the reduction of NOx and soot particle emissions: reduction in SFC (specific fuel consumption), other performance and emission characteristics. The combustion chamber geometry was modified by keeping the spark plug and the fuel injector at proper locations. The piston crown shape is modified like pent roof structure with a small bowl on one side of the pent roof (fuel injector side) to provide better turbulence, swirl and squish effects for better mixing of air with fuel. The injected fuel over a small bowl on the pent roof is directed towards the spark plug tip to initiate the combustion process. The fuel injection pressure was optimized at 150 bar using NI (National Instruments) fuel injection driver. The ignition timing was optimized at 10° bTDC using a self-developed ignition driver circuit and the fuel injection timings were optimized using NI fuel injection driver. The compression ratio of an engine was maintained at 10:1 while modifying a piston crown shape. The exhaust gas recirculation was optimized at 10%. With an optimized control parameters, the combined air-wall-guided combustion chamber geometry GDI engine with alcoholic fuel blends was tested towards its performance and emission characteristics.

Materials and methods
Combined air-wall-guided combustion chamber geometry Figure 1 shows the modified piston shape with positions of spark plug and fuel injector for a combined air-wall-guided combustion chamber geometry. The modified piston crown shape has a pent roof structure with a small bowl on one side of the pent roof surface (fuel injections side) to divert the injected fuel towards the spark plug tip in order to initiate the combustion of fuel with air. Figure 2 shows the modified cylinder head with the provisions for fixing the spark plug, fuel injector and the pressure transducer. Separate sleeves were machined and welded through cylinder head using TIG welding, as per the positions mentioned over the piston crown in Fig. 1.

Properties of oxygenated fuels used
The alternate fuels used in the experimental study are ethanol, methanol and N-butanol. The proportions of 20, 35 and 50% by volume alcohol-gasoline blends were prepared. Table 1 shows the physio-chemical properties of the mentioned blend fuels as well as gasoline. The octane number and density properties of each oxygenated fuel were higher than gasoline. However, the lower heating value of each oxygenated fuel was lower than gasoline.
Methanol is a colourless, alcoholic odour, flammable and volatile liquid, miscible with organic solvents and water. It has significantly higher octane number than gasoline. Low vapour pressure at higher concentrations will affect cold start performance of an engine and also evaporative emissions. High CR is required to operate an engine with methanol due to its higher latent heat of vaporization which cools down the intake and allows more amount of fuel into the cylinder for combustion. There were less soot emissions from an engine exhaust with methanol because of its higher oxygen content and no carbon to carbon bonding. Due to lower heating value of methanol, it requires modification of fuel supply system. Methanol blends with gasoline results in tendency of vaporization in fuel line, corrosive, chemical degradation and wear of fuel supply system components. Hence, lubricate additives were required.
Ethanol is an aromatic, olefin and sulphur-free compound. It has oxygen content of about 35% and 10% of ethanol equivalent to 3.7 wt% oxygen in gasoline. With high octane number of ethanol, higher thermal efficiency can be achieved with controlled engine knock. Ethanol blend increases its vapour pressure with blending ratios from 5 to 10% and then gradually decreases. With ethanol blend, more energy is needed to evaporate the fuel due to higher heat of vaporization which results in lower in-cylinder temperature. Also the cooled intake air increases its density and allows more fuel to be injected, which results in increased thermal efficiency. NOx emissions were reduced due to lower incylinder temperature. Lower heating value of ethanol than gasoline fuel leads to increased volumetric fuel consumption with ethanol blend. Ethanol has slightly higher density than gasoline which improves the volumetric fuel economy to some extent. Acetic acid as weak acidity content present in the ethanol may affect long-term durability, and strong acidity content may produce rapid corrosion.
N-Butanol has minimum miscibility with water but easily soluble with ethers, alcohol, glycols and hydrocarbons. It is highly flammable with flash point of around 35 °C. It can be naturally produced by fermentation of sugars and  carbohydrates. It has lower vapour pressure with gasoline blend results in cold start problems with higher blend proportions and has higher heating value than gasoline fuel.

Methodology
The various gasoline fuel blends of methanol M20, M35 and M50; fuel blends of ethanol E20, E35 and E50; fuel blends of N-butanol B20, B35 and B50 are prepared before the start of experiments. The performance characteristics of the engine and the emissions from the exhaust has to be evaluated in order to find the merits and drawbacks of all the fuel blends when compared with gasoline at the same running conditions. The tests were conducted at constant 1500 rpm speed, compression ratio of 10:1, 10% EGR, 150 bar FIP with three split injections at different durations. The fuel supply system was controlled with the help of National Instruments fuel injection driver. The ignition timing was adjusted using Arduino controller and L298N motor drivers.

Experimental setup
The test was conducted on a modified GDI engine where the 5hp, four-stroke, single cylinder diesel engine at CR (compression ratio) of 16.5:1 and the engine displacement volume of 552.3 cc was modified into a gasoline DI engine at compression ratio of 10:1. The tests were carried out on a test bed with eddy current dynamometer, and the block diagram of the GDI engine test bench is as shown in Fig. 3. Fuel rail pressure and injection system was controlled by the National Instruments fuel injection driver and Ignition timing was controlled by self-developed ignition driver circuit. During tests, the concentrations of each emission were continuously recorded with the help of AVL gas analyser and the fuel consumption was measured with the use of weighing balance. All the blends are tested under constant speed of 1500 rpm, 10% EGR (exhaust gas recirculation), 150 bar FIP (fuel injection pressure) and split injections at 320°, 220° and 100° before TDC with different injection durations of 1.0 ms, 1.1 ms and 0.9 ms respectively. The engine loading was done through eddy current dynamometer with controller. The proportions of 20, 35 and 50% of gasohol blends were tested at different loading under steady state. The various parameters are evaluated such as indicated mean effective pressure, specific fuel consumption, carbon monoxide, un-burnt hydrocarbons, oxides of nitrogen and soot emission.

Uncertainty analysis
The evaluated uncertainty of variables such as HC, CO, NOx, soot and in-cylinder pressure using AVL's 444 digas analyser, 437C smoke meter, and Kistler piezoelectric pressure transducer instruments is shown in Table 2. The error in the output results is due to environmental variations, calibration, observations, etc. Using a differential method, an error examination was made to endorse the accuracy of the experimental results. Error 'r' as a dependent variable of C 1 , C 2 , C 3 ….. C n and it can be represented by: Fig. 3 Block diagram of modified combined air-wall-guided mode GDI engine Utilizing the uncertainties of devices indicated in Table 2 computed the uncertainty values of emission characteristics. The error depends on parameters C 1 , C 2 , C 3 ,……….C n which can be estimated by: Expressed each variable error by Δc 1 /c 1 , where ΔC 1 is the precise value of the measuring instrument, c 1 is the minimal rate. Utilizing the uncertainty of individual devices determined the overall-uncertainty and it may be evaluated by:

Results and discussion
The air-wall-guided mode modified GDI engine was tested with the mentioned proportions of gasohol blended fuels at 1500 rpm, 10% EGR and fuel injection pressure of 150 bar with three split injections at 320°, 220° and 100° before TDC at different injection durations of 1.0 ms, 1.1 ms and 0.9 ms respectively. The fuel consumption was calculated using weighing balance and manual calculations. From the calculated values of SFC and IMEP, also from the measured emission values of CO, HC, NOx and Soot, the graphs were drawn for all these parameter with respect to engine torque at no load, 25% load, 50% load, 75% load and 100% load.

Performance analysis
The combined air-wall-guided mode modified GDI engine was tested for SFC and IMEP with the mentioned gasohol blended fuels at the specified fixed conditions. The engine fuel consumption was measured using weighing balance; (1) SFC and IMEP were calculated at various loads/torque values.

Specific fuel consumption analysis
The SFC gradually decreases with the increase of engine torque from low load to high load. Figure 4 shows the variation of SFC of gasoline and various alcoholic fuel blends at different proportions with various torque values. Generally, the SFC of alcoholic fuel blends increases with the increase of percentage of blend ratio. The SFC of all alcoholic blended fuels was increased with the increase of different proportions than gasoline except for E20 blended fuel. SFC of E20 blend was lower than gasoline and it higher than gasoline for E35 and E50 blends. E20 blended fuel shown a maximum decrement of SFC up to 7.2%, due to rich in heat vaporization. The SFC of N-butanol fuel blends were higher than Ethanol fuel blends, because of comparatively higher percentage of oxygen content. The SFC of Methanol fuel blends were comparatively higher than gasoline and other blend fuels because of very low calorific value and higher % weight of oxygen. For both methanol and N-butanol fuel blends, its SFC were higher at 50% blend ratios (Abdulazeez et al. 2018) with increments up to 9.2% and 7.8% respectively when compare with gasoline fuel.

Indicated mean effective pressure analysis
IMEP values of gasoline and other fuel blends increases with an increase of torque from low load to high load. Figure 5 shows the variation of IMEP of gasoline and various alcoholic fuel blends at different proportions with various torque values. From the graphical variations, it is observed that the IMEP values of methanol-gasoline and N-butanol-gasoline fuel blends were decreased with the increase of blend ratios whereas the IMEP of ethanol-gasoline fuel blends increased with an increase of blend ratio.
The IMEP of ethanol fuel blends were comparatively higher than gasoline and other fuel blends because of higher latent heat of vaporization property, better mixing of air with fuel blend and superior combustion. E20 blend develops maximum IMEP of 8.3% at 50% blend proportion and as significant increment of 7.4% at 20% of blend proportion. IMEP of methanol and N-butanol fuel blends were lower than gasoline, but higher at 20% proportion than 35% and 50% proportions. IMEP of N-butanol-gasoline fuel blends were comparatively higher (Gorbatenko et al. 2019) than methanol-gasoline fuel blends because of higher calorific value of N-butanol fuel.

Emissions analysis
The combined air-wall-guided mode modified GDI engine was tested for CO, UBHC, NOx and soot emissions with the mentioned gasoline blended fuels at the specified fixed conditions. The emission concentrations of CO, UBHC, NOx and soot were measured at various loads/torque values using AVL's 444 Digas analyser and 437C smoke meter. Figure 6 shows the variation of CO emission from gasoline and various alcoholic fuel blends at different proportions with various torque values. It is observed that the CO emissions were decreased for gasoline and all alcoholic fuel blends with an increase of torque. CO emissions were deceased with an increase of percentage of blend ratios of methanol, ethanol and N-butanol from 20 to 50%, because of increase oxygen content in the blend with an increase of SFC. From the results, it is clear that the maximum reduction of CO emission exists at 50% of blend ratios of ethanolgasoline, methanol-gasoline and N-butanol-gasoline (Liu et al. 2019;Abdulazeez et al. 2018) respectively at 12%, 13% and 12.2%. But significant reduction of CO emission (Tibaquira et al. 2018;Iodice et al. 2017)   M20 and B20 blended fuels respectively at 11.3%, 12% and 11.52%. CO emissions from methanol-gasoline fuel bends show higher decrement than ethanol-gasoline and N-butanol gasoline fuel blends, because of higher percentage of oxygen content with the methanol fuel. The percentage of CO emission formation is directly proportional to the percentage of oxygen content in the blended fuel used (or) increase in SFC. Figure 7 shows the variation of UBHC emission from gasoline and various alcoholic fuel blends at different proportions with various torque values. It is observed that the UBHC emissions from gasoline and all alcoholic gasoline fuel blends were decreased with an increase of torque. UBHC emissions of all alcoholic fuel blends with different proportions were lower than gasoline. UBHC emissions were reduced gradually from 20 to 50% of methanol-gasoline and N-butanol gasoline blended fuels (Abdulazeez et al. 2018) and shows maximum decrement of 17.5% and 16.2% respectively. But for ethanolgasoline fuel blends, UBHC emissions show a significant reduction of 14% for E20 blended fuel (Karthikeyan et al. 2017;Tibaquira et al. 2018;Iodice et al. 2017;Ribeiro et al. 2018) and maximum reduction of 20.3% for E50 fuel.

Un-burnt hydrocarbon emission analysis
At 20% blend proportions, UBHC emissions were higher for methanol-gasoline blend than ethanol-gasoline and N-butanol gasoline blended fuels (Liu et al. 2019) due to lower calorific value of methanol fuel. Oxides of nitrogen emission analysis Figure 8 shows the variation of NOx emission from gasoline and various alcoholic fuel blends at different proportions with various torque values. Generally, the NOx emission concentrations were increased with an increase of torque. NOx emissions were increased from 20 to 35% of proportions of ethanol-gasoline, methanol-gasoline and N-butanol gasoline blended fuels and then decreased with an increase of blend ratios. Both methanol-gasoline and N-butanol gasoline fuel blends show lower NOx emission concentrations (Liu et al. 2019) at 50% blend ratio and higher at 35% blend ratio. At 50% blend ratio, methanol-gasoline and N-butanol gasoline blended fuels show maximum decrement of NOx emissions up to 5.8% and 7.4% respectively. Ethanol-gasoline fuel blend shows lower NOx emission concentration at 20% blend ratio (Turner et al. 2013;Iodice et al. 2017) and higher at 35% blend ratio. At 20% blend ratio, ethanol-gasoline blended fuel shows maximum decrement of 13.3% (Tamilvanan et al. 2021) than methanol-gasoline and N-butanol gasoline blended fuels. Methanol-gasoline blended fuel at various proportions/ratios shows higher NOx emission concentrations compared to other alcoholic fuel blended fuels. Figure 9 shows the variation of soot particle emission from gasoline and various alcoholic fuel blends at different proportions with various torque values. From the graph, it is clear that the soot particle emission concentrations from gasoline fuel and all alcoholic-gasoline blended fuels were reduced with an increase of torque. Ethanol-gasoline, methanol-gasoline and N-butanol gasoline blended fuels at proportions of 20%, 35% and 50% show lower soot particle emission concentrations than gasoline. With an increase of blend ratio from 20 to 50% of methanol and N-butanol with gasoline, the soot particle emission concentrations were decreased gradually (Liu et al. 2019) and show a maximum decrement of 23.8% and 16% respectively. Ethanol-gasoline blended fuel shows a significant reduction of soot particle emission up to 27% at 20% of ethanol blend and a maximum reduction up to 33.34% at 50% of ethanol blend. Also, the soot emissions concentration were higher for N-butanol fuel blends than methanol and ethanol fuel blends because of higher calorific value of N-butanol.

Conclusion
In this experiment, the effects of methanol-gasoline, ethanolgasoline and N-butanol-gasoline on the fuel consumption, exhaust emissions and running performance of a combined air-wall-guided mode GDI engine were analysed. The tests were carried out at steady state with the blend ratios of 20, 35 and 50% by volume. The obtained results were compared with the characteristics of gasoline. The variations are summarized and listed below: • IMEP of methanol gasoline fuel blends were comparatively lower than ethanol-gasoline and N-butanol fuel blends because of lower calorific value and higher oxygen content of methanol fuel. The SFC of Methanolgasoline fuel blends was higher than gasoline and other gasohol blends in each blend ratio. SFC of methanolgasoline blends were higher at 50% blend ratio with increment up to 9.2% when compare with gasoline fuel. Significant reduction of CO emission up to 12% for M20 blend and maximum reduction of 13% for M50 blend. HC emissions were decreased gradually with an increase of blend ratio, and it reached maximum reduction of 17.5% for M50 blend. NOx emissions shown lower for M50 blend with a decrement of 5.8% and higher for M35 blend. Soot particle emissions were decreased gradually with an increase of blend ratio, and it reached maximum reduction of 23.8% for M50 blend. • IMEP values of N-butanol gasoline fuel blends were decreased with the increase of blend ratios. IMEP of N-butanol fuel blends were lower than gasoline, but higher at 20% proportion than 35% and 50% proportions. IMEP of N-butanol gasoline fuel blends were comparatively higher than methanol-gasoline fuel blends because of higher calorific value of N-butanol fuel, but lower than ethanol-gasoline fuel blends. The SFC of N-butanol gasoline fuel blends were higher than gasoline and ethanol-gasoline blended fuels in each blend ratio. SFC of N-butanol gasoline blends were higher at 50% blend ratio with increment up to 7.8% when compared with gasoline fuel. Significant reduction of CO emission up to 11.52% for B20 blend and maximum reduction of 12.2% for B50 blend. HC emissions were decreased gradually with an increase of blend ratio, and it reached maximum reduction of 16.2% for B50 blend. NOx emissions shown lower for B50 blend with a decrement of 7.4% and higher for B35 blend. Soot particle emissions were decreased gradually with an increase of blend ratio, and it reached maximum reduction of 16% for B50 blend. • IMEP of ethanol-gasoline fuel blends increased with an increase of blend ratio. The IMEP of ethanol fuel blends were comparatively higher than gasoline and other fuel blends. E20 blend develops maximum IMEP of 8.3% at 50% blend proportion and as significant increment of 7.4% at 20% of blend proportion. The SFC of ethanol gasoline fuel blends were lower than methanol-gasoline and N-butanol gasoline fuel blends. SFC of E20 blend was lower than gasoline and it was higher than gasoline for E35 and E50 blends. E20 blended fuel shown a maximum decrement of SFC up to 7.2%. Significant reduction of CO emission up to 11.3% for E20 blend and maximum reduction of 12% for E50 blend. HC emissions were decreased significantly up to 14% for E20 blend and it reached maximum reduction of 20.3% for E50 blend. NOx emissions shown lower for E20 blend with a decrement of 13.3% and higher for B35 blend. Soot particle emissions were decreased significantly up to 27% for E20 blend and it reached maximum reduction of 33.34% for E50 blend.
From the discussion over the results obtained, the ethanol 20% blend with gasoline shows major beneficial environmental impact towards emissions reduction than other alcoholic fuels when tested with the combined air-wallguided combustion chamber geometry GDI engine at the specified operating conditions. Author contribution Shivakumar N: conceptualization, methodology, investigation, resources, data curation, writing-original draft, review and editing, visualization. Dr. Kumaresan G: investigation, supervision, project administration, writing-review and editing.

Data availability
The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Declarations
Ethics approval The authors declare that the submitted manuscript is original. They acknowledge the current review has been conducted ethically, and the final shape of the research has been agreed upon by all authors.

Consent to participate
The authors consent to participate in this research study.