The use of bioethanol in the transport sector can contribute to mitigate the greenhouse gas emissions of the vehicles. To achieve this goal, together with a positive energy balance in global productive process of ethanol (well to tank), it is important that adding ethanol to gasoline does not cause a worsening of the efficiency of the internal combustion engine (tank to wheel). In this paper, a research activity on a commercial spark-ignition light-duty engine at the test bench is reported. The aim of the work was to characterize the effect of different bioethanol/gasoline blends on engine behaviour. Blends until 85% of ethanol were tested. Comparative studies of combustion development of gasoline and gasoline/ethanol blends at different concentrations have been made through the analysis of pressure cycles in combustion chamber. Moreover, emissions were collected and analyzed. Emissions downstream of the catalyst, measured with the blends, resulted quite similarly to the gasoline case. Instead, upstream the catalyst a reduction of emissions, proportional to oxygenated content was noted. Moreover, a general carbon dioxide reduction with ethanol blends was achieved due in particular to better engine thermal efficiency.
The increasing costs and climate change related to fossil fuels exploitation require a major share of the energy production from alternative sources, in particular from waste or renewable sources. Recently, great attention is given to the use of biomass to produce fuels, especially for transport as alternative to petrol. Biofuels production becomes extremely interesting when obtained from waste or residual of other human activities, but in this case, the limited feedstock could contribute only with a small impact on the reduction of the fossil fuel demand. The use of bioethanol in the transport sector can contribute to mitigate the greenhouse gas emissions of the vehicles. The benefits are strictly connected with the efficiency of ethanol global productive process, taking into account also land use competition with other human needs.
The octane number of pure ethanol is higher than gasoline; therefore, it is an optimal fuel to improve performance of Otto engines since the risk of knock decreases [
The influence of alcohol/gasoline blends on spark ignition internal combustion engine performance and emissions was largely investigated. Bibliographic data highlight a general reduction of engine-out emission [
In this paper, gasolines E10, E20, E30, and E85 (resp. 10%, 20%, 30%, and 85% v/v of ethanol in gasoline) were tested on commercial light duty engine for passengers car at the test bench to valuate in particular the effect of ethanol content on thermal efficiency at parity of in-cylinder cycle pressure.
The planned objective of the experimental activity was the characterization of engine behaviour with different gasoline/ethanol blends in terms of emissions and performance, mainly efficiency and combustion development. The engine used in the tests was a 1.6-litre spark ignition engine equipped with a three-way catalyst (TWC) at the exhaust, whose main characteristics are reported in Table
Engine main characteristics.
Naturally aspirated 4-cylinder in-line, stoichiometric spark ignition | |
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Bore × stroke | 80.5 mm × 78.4 mm |
Total displacement | 1596 cm3 |
Volumetric compression ratio | 10.5 : 1 |
Rated power | 76 kW at 5750 rpm |
Rated torque | 144 Nm at 4000 rpm |
Number of valves per cylinder | 4 (2 for intake—2 for exhaust) |
NG feeding system | Electronic timed multipoint injection |
Spark ignition engine at the test bed.
For optimization of engine parameters and electronic control unit (ECU) data storage, the Magneti Marelli Helios board with dedicated software has been used. Before starting experimental activity, engine head has been substituted in order to install a pressure transducer in the combustion chamber of cylinder no. 3 and some thermocouples to monitor the head temperature in significant points, such as the seat between intake and exhaust valve, the zone close to the spark plug. In Figure
Engine head equipped with the seat for the pressure transducer and some thermocouples.
Gaseous emissions have been measured with a hot Beckman 404 flame ionization detector (FID) for THC, a hot ABB UV Limas 11 for nitrogen oxides (
The tests have been performed with pure gasoline and increasing the ethanol content by volumes of 10, 20, 30, and 85%.
In Table
Gasoline, ethanol, and tested blends main characteristics.
A/F | LHV |
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Ethanol | C | H | O | gCO2/MJ |
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kg/kg | MJ/kg | kg/m3 | % mass | % mass | % mass | % mass | g/MJ | MJ/kg | kJ/kg | |
Gasoline | 14.32 | 42.5 | 750 | 0 | 85 | 13 | 1 | 73.4 | 2.77 | 400 |
E10 | 13.77 | 40.9 | 754 | 10 | 82 | 13 | 5 | 73.3 | 2.77 | — |
E20 | 13.22 | 39.3 | 757 | 20 | 78 | 13 | 8 | 73.1 | 2.76 | — |
E30 | 12.68 | 37.7 | 761 | 30 | 75 | 13 | 12 | 72.9 | 2.75 | — |
E85 | 9.77 | 29.2 | 780 | 85 | 57 | 13 | 30 | 71.5 | 2.71 | — |
Ethanol | 9.01 | 26.9 | 785 | 100 | 52 | 13 | 35 | 71.0 | 2.69 | 850 |
aHeat content of stoichiometric mixture.
bLatent heat of vaporization.
The lower heating value (LHV) of gasoline reported in Table
The tests have been carried out on a grid of nine speed/load conditions, ranging from 1750 to 3000 rpm and from 20 to 80 Nm (Table
Test conditions with gasoline and ethanol/gasoline blends.
Speed | Torque/BMEP | ||
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rpm | Nm/bar | ||
1750 | 20/1.9 | 50/4.1 | 80/6.6 |
2050 | 20/1.9 | 50/4.1 | 80/6.6 |
3000 | 20/1.9 | 50/4.1 | 80/6.6 |
The engine was tested in closed-loop stoichiometric condition, assured by ECU. Instead, spark advance (SA) has been optimized, with a calibration tool software (HELIOS), to have the peak pressure at 13÷16 crank angle degree (CAD) after top dead centre, for all the tested blends. SA was changed with respect to that set by the standard ECU for two reasons. The standard ECU follows as SA strategy to reduce emissions on the NEDC cycle, and therefore, in some conditions, it achieves a combustion delayed with respect to the optimal angle to reduce Furthermore, the ECU showed a trend to reduce SA at ethanol content increasing. At steady-state condition, the ECU sets the SA principally on the base of engine coolant temperature, speed, and manifold absolute pressure (MAP). With all the tested blends at each speed and load condition no difference on MAP was found, since the heat content of stoichiometric air/fuel mixture is almost not influenced by the content of ethanol in the blend, and therefore, the engine must intake the same total mass (air + fuel). At the same engine speed and MAP, the ECU should set the same SA. Instead, the lower SA that ECU sets at ethanol content increasing could be due to the self-adaptive algorithms implemented in the ECU and influenced by the comparison between the mapped value of the injection time to a given load and the value set to have a stoichiometric mixture. In fact, the increase of the ethanol content, in closed-loop condition, leads to larger injection times to maintain the stoichiometric mixture at a given load.
In Table
Spark advance, manifold absolute pressure, and throttle position for all the tested fuels.
Gasoline | E10 | E20 | E30 | E85 | |||||||||||
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SA | MAP | TP | SA | MAP | TP | SA | MAP | T.P. | SA | MAP | T.P. | SA | MAP | T.P. | |
[CAD] | [mbar] | ° | [CAD] | [mbar] | ° | [CAD] | [mbar] | ° | [CAD] | [mbar] | ° | [CAD] | [mbar] | ° | |
1750 and 20 | 37.6 | 414 | 7 | 37.8 | 412 | 7 | 37.2 | 405 | 7 | 36.9 | 393 | 7 | 35.1 | 422 | 6 |
1750 and 50 | 30.5 | 605 | 11 | 31.1 | 595 | 11 | 30.6 | 592 | 11 | 30.5 | 585 | 11 | 29.5 | 607 | 10 |
1750 and 80 | 27.7 | 791 | 15 | 27.8 | 783 | 15 | 27.6 | 776 | 15 | 27.4 | 782 | 16 | 25.8 | 791 | 15 |
2050 and 20 | 41.5 | 384 | 8 | 44.2 | 375 | 7 | 41.8 | 381 | 8 | 42.2 | 375 | 9 | 40.5 | 386 | 7 |
2050 and 50 | 31.1 | 565 | 12 | 35.0 | 571 | 12 | 34.1 | 568 | 12 | 34.4 | 558 | 13 | 33.0 | 569 | 11 |
2050 and 80 | 29.6 | 751 | 16 | 32.1 | 738 | 16 | 31.5 | 740 | 16 | 31.9 | 733 | 17 | 29.9 | 748 | 16 |
3000 and 20 | 41.7 | 405 | 9 | 41.8 | 404 | 9 | 41.7 | 408 | 9 | 41.5 | 419 | 11 | 37.8 | 405 | 8 |
3000 and 50 | 34.3 | 578 | 15 | 34.4 | 575 | 14 | 35.6 | 559 | 14 | 34.1 | 595 | 16 | 33.5 | 570 | 14 |
3000 and 80 | 29.0 | 756 | 20 | 32.1 | 751 | 19 | 32.0 | 748 | 20 | 31.6 | 775 | 21 | 29.1 | 754 | 19 |
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Mean value |
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Fuel mass flow rate, injection time, and fuel volume flow rate as mean values of the experimental points.
Anyway, the observed fuel mass increasing with ethanol content is appreciably lower than that predictable on the base of tested fuel characteristics. In Figure
Theoretical and experimental values of fuel consumption and CO2 emissions.
In Figure
Engine efficiency as mean value of the nine experimental points.
The improved efficiency obtained with the addition of ethanol may be justified by several causes. First of all, the higher oxygen content of the fuel gives a better combustion. In Figure
Engine-out THC emission as mean value of the nine experimental points.
Combustion efficiency at different engine speeds as a function of ethanol content in blends.
Also, the combustion speed was improved with ethanol, even if of slight amount. The combustion duration, valuated as the time between the SA and the 90% fuel mass burned, was reduced (Figure
Combustion duration at parity of BGC as mean value of the experimental grid.
In-cylinder pressure at 4.1 bmep load at 3000 and 1750 rpm for the tested blends.
As reported in Table
In-cylinder pumping cycle at 4.1 bmep at 3000 and 1750 rpm for all the tested blends.
Instead, some further benefits on efficiency could be deriven from a lower temperature intake mixture. Ethanol increases the heat of vaporization of the air fuel mixture that evaporates during compression. This makes the compression stroke more close to the isothermal one, which results in lower compression work. Some researchers tried to obtain this effect with water injection [
Intake mixture temperatures for all the tested blends as mean values of the experimental grid.
Engine head temperatures for all the tested blends as mean values of the experimental grid.
The intake mixtures temperatures (Figure
The effect of ethanol on reducing the temperature of the mixture could also be derived from the
Engine-out
A traditional port injection spark-ignited engine was found to be not significantly influenced by the content of ethanol in gasoline. The engine was fuelled with blends until 85% by volume of ethanol. The standard ECU was able to control air/fuel composition retaining the target stoichiometric value with regular operation. Instead, spark advance set by the original ECU is affected by the ethanol content at parity of engine load, probably due to the injection time increasing that affects the logic controller. In the experimental activity, SA has been modified using a calibration tool software to compare the engine behaviour with all the tested blends at parity of in-cylinder cycle development.
A positive trend between the ethanol content and efficiency of the engine was found. In the paper, the efficiency improvement was analyzed with the available experimental data and considering a range of variability of gasoline lower heating value of