Conventional Diesel Combustion Research Articles

Influence of the diesel pilot injector configuration on ethanol combustion and performance of a heavy-duty direct injection engine

Thanks to its properties and production pathways, ethanol represents a valuable alternative to fossil fuels, with potential benefits in terms of CO2, NOx, and soot emission reduction. The resistance to autoignition of ethanol necessitates an ignition trigger in compression-ignition engines for heavy-duty applications, which in the current study is a diesel pilot injection. The simultaneous direct injection of pure ethanol as main fuel and diesel as pilot fuel through separate injectors is experimentally investigated in a heavy-duty single cylinder engine at a low and a high load point. The influence of the nozzle hole number and size of the diesel pilot injector on ethanol combustion and engine performance is evaluated based on an injection timing sweep using three diesel injector configurations. The tested configurations have the same geometric total nozzle area for one, two and four diesel sprays. The relative amount of ethanol injected is swept between 78 – 89% and 91 – 98% on an energy basis at low and high load, respectively. The results show that mixing-controlled combustion of ethanol is achieved with all tested diesel injector configurations and that the maximum combustion efficiency and variability levels are in line with conventional diesel combustion. The one-spray diesel injector is the most robust trigger for ethanol ignition, as it allows to limit combustion variability and to achieve higher combustion efficiencies compared to the other diesel injector configurations. However, the two- and four-spray diesel injectors lead to higher indicated efficiency levels. The observed difference in the ethanol ignition dynamics is evaluated and compared to conventional diesel combustion. The study broadens the knowledge on ethanol mixing-controlled combustion in heavy-duty engines at various operating conditions, providing the insight necessary for the optimization of the ethanol-diesel dual-injection system.

Effects of fuel oxygenation and ducted fuel injection on the performance of a mixing-controlled compression-ignition optical engine with a two-orifice fuel injector

This paper describes results from an optical-engine investigation of oxygenated fuel effects on ducted fuel injection (DFI) relative to conventional diesel combustion (CDC). Three fuels were tested: a baseline, non-oxygenated No. 2 emissions certification diesel (denoted CFB), and two blends containing potential renewable oxygenates. The first oxygenated blend contained 25 vol% methyl decanoate in CFB (denoted MD25), and the second contained 25 vol% tri-propylene glycol mono-methyl ether in CFB (denoted T25). Whereas DFI and fuel oxygenation primarily curtail soot emissions, intake-oxygen mole fractions of 21% and 16% were employed to explore the potential additional beneficial impact of dilution on engine-out emissions of nitrogen oxides (NOx). It was found that DFI with an oxygenated fuel can attenuate soot incandescence by ~100X (~10X from DFI and an additional ~10X from fuel oxygenation) relative to CDC with conventional diesel fuel, regardless of dilution level and without large effects on other emissions or efficiency. This breaks the soot/NOx trade-off with dilution, enabling simultaneous reductions in both soot and NOx emissions, even with conventional diesel fuel. Significant cyclic variability in soot incandescence for both CDC and DFI suggests that additional improvements in engine-out soot emissions may be possible via improved control of in-cylinder mixture formation and evolution.

A comparative study of isobaric combustion and conventional diesel combustion in both metal and optical engines

Isobaric combustion is more efficient than isochoric combustion when the peak cylinder pressure is restricted. Recently a double compression expansion engine concept using isobaric combustion was proposed to improve the engine performance. However, the knowledge about the in-cylinder isobaric combustion process is limited. This study investigated isobaric combustion in both metal and optical engines utilizing a centrally placed direct injector and a multiple injections strategy, and the performance and emissions of isobaric combustion and conventional diesel combustion (CDC) were compared. Mie scattering and fuel-tracer planar laser-induced fluorescence (PLIF) were used to visualize the liquid-phase fuel penetration length and fuel distribution under non-reactive conditions, respectively. The natural flame luminosity and spatial soot distribution were measured with high-speed imaging and laser-induced incandescence (LII), respectively. Results demonstrate an increased soot formation in the isobaric cases compared with the CDC case. The successive fuel injection into reacting zones, which induces a locally fuel-rich mixture and less fuel–air mixing, accounts for the high soot emissions in the isobaric combustion. This study further demonstrates that the late injections of the isobaric cases lead to more combustion in the squish zone and near the cylinder walls, which increases the local temperature gradient and may result in more heat losses. There is still room to reduce the heat losses in the isobaric combustion although the total heat loss of the isobaric combustion is lower than the CDC case due to a lower combustion temperature. Multiple injectors are suggested to reduce the soot emissions of the isobaric combustion by spreading the different injections in space.

Effects of triethylene glycol mono methyl ether (TGME) as a novel oxygenated additive on emission and performance of a dual-fuel diesel engine fueled with natural gas-diesel/biodiesel

The need for energy sources is one of the major problems for all countries in the world. Biodiesel is one of the alternative fuels. The use of 5% biodiesel in diesel fuel blend is usual, and most countries have planned to use 20%. Glycerol is a by-product of biodiesel production. Therefore, due to the increase in this substance, glycerol management is substantial. In this study, biodiesel was produced by the transesterification process from waste cooking oil (WCO); then, the triethylene glycol mono-methyl-ether (TGME) as a novel additive obtained from glycerol by the etherification method. The Dual-Fuel Diesel Engine mode (DFM) is one of the most suitable ways of achieving efficient and clean combustion. Dual-fuel combustion has been performed through the use of natural-gas (NG) as the main fuel and diesel/biodiesel blend The DFDEm engine was run under three different high NG ratios (60, 70, and 80%), at full-load and 1500rpm. Biodiesel was used at two levels of 5 and 20 vol%. TGME was added at four levels (0.1, 0.2, 0.3 and 0.4 vol.%) to fuel blends. Results showed that glycerol conversion and recycling into TGME additive is important, because, the presence of oxygen in the chemical structure of the TGME additive can make it a suitable oxygenated additive. The TGME as an oxygenated additive improved the most parameters of the engine. Oxygenated fuels contributed to the combustion process and improved it. The best conditions achieved by adding 0.2 vol% TGME additive into diesel fuel at the DFM engine in NG70 mode, under these conditions in comparison to conventional diesel combustion brake power, and brake thermal efficiency increased by 10.54 and 12.77%, but the generated power cost amount decreased by 20.16%. Also CO, CO2, and NOx emissions decreased by 76.77, 40.9, 1.31%, respectively.

Individual cylinder fuel blend estimation in a dual-fuel engine using an in-cylinder pressure based observer

Cylinder-to-cylinder combustion dispersion in internal combustion engines might be caused by various factors (e.g. manufacturing variations of the injectors or nozzle coking) which can result in an increase in pollutant emissions. When dealing with low temperature combustion concepts such as premixed dual-fuel, the system might suffer from an additional source of dispersion due to port fuel injection distribution. Conventional cylinder fuel concentration estimation is based on look-up tables previously calibrated and saved in the ECU. The aging and the fuel distribution characterization of the injectors are a challenging task when relying only on a single UEGO sensor placed at the exhaust. In-cylinder pressure sensors offer a powerful solution to evaluate the energy released by the fuel with one cycle resolution. The present work proposes to combine the information provided by such sensor together with conventional sensors, in this case air mass flow and lambda sensor, for estimating the fuel concentration and blending ratio entering each cylinder in a heavy-duty dual-fuel engine. A Kalman filter was designed to tackle the dynamics of the system, e.g. lambda sensor delay and port fuel distribution, and validated in both conventional diesel and dual-fuel combustion. The output of the filter was then used to update the injectors look-up table in order to cope with aging and possible bias over time.

Optimization of gasoline compression ignition combustion with ozone addition and two-stage direct-injection at middle loads

Ozone (O3) was introduced into the intake air to control the ignition in a gasoline compression ignition (GCI) engine. An early fuel injection at −68 °CA ATDC was adopted to mix the fuel with the reactive O-radicals decomposed from the O3, before the reduction of the O-radicals due to their recombination would take place. The second injection was implemented near top dead center to optimize the profile of the heat release rate. The engine experiments were performed around the indicated mean effective pressure (IMEP) of 0.67 MPa with a primary reference fuel, octane number 90 (PRF90), maintaining the 15% intake oxygen concentration with the EGR. The quantity of the first injection, the second injection timing as well as the ozone concentration were changed as experimental parameters. The results showed that the GCI operation with the ozone addition makes it possible to reduce the maximum pressure rise rate while attaining high thermal efficiency, compared to that without the ozone. Appropriate combinations of the ozone concentration and the first injection quantity achieve low smoke and NOx emissions. Further, the ozone-assisted GCI operation was compared with conventional diesel operation. The results showed that the indicated thermal efficiency of the ozone-assisted GCI combustion is slightly lower than that of the conventional diesel combustion, but that GCI assisted with ozone is highly advantageous to the smoke and NOx emissions.

EXPERIMENTAL INVESTIGATION OF DIESEL-ETHANOL FUEL BLENDS IN A COMPRESSION IGNITION ENGINE

Depletion of fossil fuels and environmental pollution has led researchers to foresee the need to develop bio-fuels. Alcohols are a major part of bio-fuels. This study debates combustion performance and exhaust emissions from CI engine fueled with diesel-ethanol blends. The fuel blends contained % 100 diesel (E0), % 90 diesel - % 10 ethanol (E10) and % 80 diesel - % 20 (E20) ethanol by volume. Tests were conducted at %0, %25, %50, %75 and %100 load conditions at various ethanol mass. The effects of blended fuels on engine performance were investigated and results showed that E10 presents the highest volumetric efficiency; on the other hand E20 showed the lowest volumetric efficiency. Maximum in-cylinder pressure was occured conventional diesel combustion. Results indicated that the concentrations of CO2 and HC(unburnt hydrocarbons) emissions weren’t significant difference. E10 presented the lowest CO emission at all engine loads. In addition to this NO emission was peaked on E20 at %75 load.

PRELIMINARY STUDY OF WATER INJECTION ON THE COMBUSTION AND EMISSIONS CHARACTERISTICS IN A HCCI ETHANOL ENGINE

Our dependence on fossil fuels coupled with concerns about harmful emissions have motivated researchers to look for renewable fuels that have clean combustion and for advanced combustion modes. In this context, homogeneous charge compression ignition (HCCI) is an emerging technology which offers an alternative to conventional spark ignition and compression ignition engines and can operate on renewable fuels. Low temperature combustion, which can result in low NOx emissions with high indicated efficiency, is the more important characteristic of this combustion mode. It’s main problem is the combustion timing control due to lack of direct ignition control, once HCCI flame initiation is based on charge thermal state. Thus, controlled auto-ignition (CAI) combustion mode has been proposed. Several methods were proposed for combustion phasing control, between them, the injection of water in the intake manifold. This work investigated the influence of water injection in the intake runner of an ethanol HCCI cylinder from a converted three-cylinder diesel generator set, in which two cylinders operated on conventional diesel combustion and one diesel cylinder provided recycled exhaust gas for the one cylinder running on ethanol HCCI combustion. The water injection was used to control the CA50 combustion parameter. The results show that water injection is an efficient strategy to control the combustion timing, since the reactivity of the mixture can be controlled. The results at 400 and 600 kPa of IMEP and 1800 rpm indicated a good combustion stability, high efficiency and low emissions characteristics. The highest indicated fuel conversion efficiency found was 36.9% for 600 kPa of IMEP and 8 CAD of CA50. However, for 200 kPa of IMEP the combustion was unstable, the indicated efficiency was deteriorated and indicted CO emissions was high.

Experimental study of independent two-stage in-cylinder heat release using jet controlled compression ignition

To extend the load range of premixed combustion, the jet controlled compression ignition (JCCI) mode with dual-direct injectors was adopted in a high-speed light-duty diesel engine. The pre-mixture was flexibly prepared by the direct pre-injection of blended fuels, and the ignition timing could be controlled robustly by the diesel jet-injection. Engine experiments were conducted at 75% engine load with an engine speed of 3000 rpm. The results indicate that an obvious two-stage high-temperature heat release process is achieved by modulating the injection parameters of dual-direct injectors independently. The late combustion phasing resulted from the retarded diesel jet-injection effectively depress the reaction rate. When the pre-injection is delayed within the sensitivity interval, the local richer premixed charge accelerates the pre-mixture combustion stage. The indicated thermal efficiency is increased by 7.4%, and nitrogen oxide emission is reduced by 16.9% compared to the conventional diesel combustion mode. The increased pre-injection pressure can suppress the reaction rate but causes wall-wetting issues. The stratification of the equivalence ratio prepared by the double direct pre-injection strategy diminishes the maximum pressure rise rate by over 64% compared to that with single direct pre-injection. It is also revealed that the start of the second pre-injection plays a dominant role in modulating the combustion process, which illustrates the potential to extend the engine load of premixed combustion mode.

Impact of low NOx strategies on holistic emission reduction from a CI engine over transient conditions

The use of biofuels to replace fossil fuels as well as more stringent emission regulations for internal combustion engines cause a challenge for the engine manufacturers to build engines that can cope with a wide range of fuels, but still offer low exhaust emissions with no detriment to performance. In this work a test bed with a compression ignition engine has been used to measure emissions when using a ternary fuel blend between diesel, biodiesel and ethanol together with exhuast gas recirculation (EGR) and different fuel delivery techniques. EGR with biofuels have the potential to significantly reduce NOx over conventional diesel combustion. The fuel used, B2E9 achieves a 10% renewable content as set out in the UK government’s Renewable Energy Directive. Most studies reported in the literature evaluates emissions reduction technologies by only changing one factor-at-a-time at steady state conditions. This paper addresses these issues and presents a methodology utilising a Central Composite Design (CCD) analysis to optimise four engine parameters which include EGR percentage, main injection SOI, pilot injection SOI and pilot injection open duration over a transient drive cycle (WLTP) which makes the results more applicable to real world driving conditions. The optimisation of the CCD showed that NOx emissions decreases by 25% when the maximum exhaust gas recirculation is set to 45%, the main injection is retarded by 2 CADs, the pilot injection dwell time is set to 21 CADs and 24% of the fuel is delivered through the pilot injection. CO emissions increase by approximately 47% as a result of the decrease in NOx emissions.

A numerical investigation of isobaric combustion strategy in a compression ignition engine

Three-dimensional computational fluid dynamic simulations were conducted to study the means to achieve isobaric combustion mode in a compression ignition engine, which is intended to be used in the high-efficiency double compression-expansion engine (DCEE) concept. Compared to the conventional diesel combustion mode, the isobaric combustion mode generated a significantly lower peak combustion pressure, which was beneficial for the high load extension. For both combustion modes, the ignition was triggered downstream of the nozzle, with the heat release dominated by HCO + O2 = CO+HO2, while the injection-combustion duration for the isobaric combustion mode was significantly longer. The effects of swirl ratio, spray angle, and piston geometries on the isobaric combustion at various engine loads were also investigated. The higher swirl ratio resulted in a higher heat transfer loss and thus lower thermal efficiency. Due to the higher air utilization rates and lower heat transfer losses, cases with spray angles of 140° and 150° generated the higher thermal efficiencies. The piston bowl geometry was found to have a significant impact on the mixing and combustion processes, especially at high engine load conditions. For the conditions under study, the original piston geometry with a swirl ratio of 0 and a spray angle of 140° demonstrated the highest thermal efficiency for the isobaric combustion mode. The results of this work will provide guidance in the practical design and implementation of the DCEE concept.

Study of Ignition and Combustion Characteristics of Consecutive Injections with iso-Octane and n-Heptane as Fuels

Gasoline compression ignition (GCI) engines have potential to improve fuel economy and reduce emissions harmful to health and the environment compared with conventional diesel combustion engines. T...

Ducted Fuel Injection vs. Conventional Diesel Combustion: Extending the Load Range in an Optical Engine with a Four-Orifice Fuel Injector

Ducted Fuel Injection vs. Conventional Diesel Combustion: Extending the Load Range in an Optical Engine with a Four-Orifice Fuel Injector

Effect of reformed biogas as a low reactivity fuel on performance and emissions of a RCCI engine with reformed biogas/diesel dual-fuel combustion

Biogas can be used as a less expensive continuance renewable fuel in internal combustion engines. However, variety in raw materials and process of biogas production results in different components and percentages of various elements, including methane. These differences make it difficult to control the combustion, effectively, in internal combustion engines. In this research, under cleaning and reforming process, biogas components were fixed. Then the effect of reformed biogas (R.BG) was investigated, numerically, on the combustion behavior, performance and emissions characteristics of a RCCI engine. A 3D-computational modeling has been performed to validate a single-cylinder compression ignition engine in conventional diesel and dual-fuel operations at 9 bar IMEP, 1300 rpm. Then, the combustion model of the RCCI engine was simulated by replacing diesel fuel with 20%, 40% and 60% of R.BG as a low reactivity fuel while remaining constant input total fuel energy per cycle. The results demonstrated that when the R.BG substitution ratio increases with a constant equivalence ratio of 0.43, the mean combustion temperature decreases to 1354 K, 1312 K, 1292 K which are about 3.5%, 6.6%, 7.9% lower than the conventional diesel combustion, respectively. The maximum in-cylinder pressure increases up to 22.63%. Instead, it results in 2.3%, 7.9%, and 14.5% engine power output losses, respectively. Also, the NOx emission, against CO, is decreased by 50%. Soot and UHC emissions were found to be slightly decreased while was used R.BG more than 40%.

Prospective fuels for diesel low temperature combustion engine applications: A critical review

Low Temperature Combustion (LTC) strategies are most promising to simultaneously reduce oxides of nitrogen (NOx) and soot emissions from diesel engines along with offering higher thermal efficiency. Commercial wide spread implementation of diesel LTC strategies requires several challenges to be addressed, including lack of precise ignition timing control, widening the narrow operating load ranges and reducing high unburned fuel emissions. These challenges can be addressed through modifications in the engine or fuel design or both. The timing and rate of combustion in several LTC strategies are controlled primarily by the chemical kinetics of the fuel. Since, diesel fuel reactivity and volatility are tailor-made to perform well under conventional diesel combustion conditions, its application in LTC poses several problems, as highlighted in this paper. Hence, it is important to identify suitable alternative fuels for the different diesel LTC strategies. The published literature on LTC over the past 25 years is critically analyzed to discuss the evolution of the different diesel LTC strategies, their operability limits, the challenges and the controlling parameters for each strategy. This is followed by in-depth analysis of the role of the fuel and the fuel requirements for each strategy. Further, the importance of adopting a hybrid surrogate modeling approach to enable numerical simulation of diesel LTC is highlighted. A novel attempt of relating various diesel low temperature combustion (LTC) strategies based on the approach followed to achieve positive ignition dwell through different injection strategies, utilizing high exhaust gas recirculation (EGR), and dual fuels is presented. The need for replacing diesel with alternative liquid fuels in LTC strategies is presented by highlighting the fundamental problems associated with diesel fuel characteristics. The review concludes by suggesting potential alternative fuels for various diesel LTC strategies and provides directions for future work to address the challenges facing compression ignition LTC operation.

A Computational Investigation of the Impact of Multiple Injection Strategies on Combustion Efficiency in Diesel–Natural Gas Dual-Fuel Low-Temperature Combustion Engines

AbstractDual-fuel diesel–methane low-temperature combustion (LTC) has been investigated by various research groups, showing high potential for emissions reduction (especially oxides of nitrogen oxide (NOx) and particulate matter (PM)) without adversely affecting fuel conversion efficiency in comparison with conventional diesel combustion. However, when operated at low load conditions, dual-fuel LTC typically exhibits poor combustion efficiencies. This behavior is mainly due to low bulk gas temperatures under lean conditions, resulting in unacceptably high carbon monoxide (CO) and unburned hydrocarbon (UHC) emissions. A feasible and rather innovative solution may be to split the pilot injection of liquid fuel into two injection pulses, with the second pilot injection supporting CO and UHC oxidation once combustion is initiated by the first one. In this study, diesel–methane dual-fuel LTC is investigated numerically in a single-cylinder heavy-duty engine operating at 5 bar brake mean effective pressure (BMEP) at 85% and 75% percentage of energy substitution (PES) by methane (taken as a natural gas (NG) surrogate). A multidimensional model is first validated in comparison with the experimental data obtained on the same single-cylinder engine for early single pilot diesel injection at 310 crank angle degrees (CAD) and 500 bar rail pressure. With the single pilot injection case as baseline, the effects of multiple pilot injections and different rail pressures on combustion and emissions are investigated, again showing good agreement with the experimental data. Apparent heat release rate and cylinder pressure histories as well as combustion efficiency trends are correctly captured by the numerical model. Results prove that higher rail pressures yield reductions of HC and CO by 90% and 75%, respectively, at the expense of NOx emissions, which increase by ∼30% from baseline still remaining at very low level (under 1 g/kWh). Furthermore, it is shown that postinjection during the expansion stroke does not support the stable development of the combustion front as the combustion process is confined close to the diesel spray core.

Effect of operating conditions on the chemical composition, morphology, and nano-structure of particulate emissions in a light hydrocarbon premixed charge compression ignition (PCCI) engine

The aim of present work is to bridge the gap of knowledge concerning crystallite size, graphene layers curvature and inter-layer distance as nanostructure characteristics of soot primary particles, and also to comprehensively characterize the morphology of soot emission in a light hydrocarbon premixed charge compression ignition (PCCI) engine. In this study, the chemical composition, morphology and nano-structure of particulate emissions between conventional diesel and light hydrocarbon PCCI engine were performed with thermogravimetric analysis, gas chromatography mass spectrometry, and high-resolution transmission electron microscopy technology. The results show that the volatile matter content of light hydrocarbon is much higher than that of diesel, and thermogravimetry and differential thermogravimetry curves of light hydrocarbon shift to low temperature regions. The total organic components of particulate matter of light hydrocarbon PCCI engine are less, and the corresponding separation time is shorter. The structure of particles produced in light hydrocarbon PCCI engine is more open, and the size of aggregates is smaller. Fractal dimensions of 1.774 and 1.691 are obtained for soot particles in light hydrocarbon PCCI engine, compared to that of 1.81 and 1.785 in conventional diesel engine. Compared to conventional diesel engine, fringe separation distance and fringe tortuosity in light hydrocarbon PCCI engine are smaller while fringe length is larger. The primary particle nanostructures of light hydrocarbon PCCI engine incline to graphitize and change into the orderly structure. Compared with conventional diesel combustion, the average primary particle diameter of light hydrocarbon PCCI approximately reduces 2.0% at 75% load and 18.2% at 100% load, respectively.

1D Simulation and Experimental Analysis on the Effects of the Injection Parameters in Methane–Diesel Dual-Fuel Combustion

Notwithstanding the policies that move towards electrified powertrains, the transportation sector mainly employs internal combustion engines as the primary propulsion system. In this regard, for medium- to heavy-duty applications, as well as for on- and off-road applications, diesel engines are preferred because of the better efficiency, lower CO2, and greater robustness compared to spark-ignition engines. Due to its use at a large scale, the internal combustion engines as a source of energy depletion and pollutant emissions must further improved. In this sense, the adoption of alternative combustion concepts using cleaner fuels than diesel (e.g., natural gas, ethanol and methanol) presents a viable solution for improving the efficiency and emissions of the future powertrains. Particularly, the methane–diesel dual-fuel concept represents a possible solution for compression ignition engines because the use of the low-carbon methane fuel, a main constituent of natural gas, as primary fuel significantly reduces the CO2 emissions compared to conventional liquid fuels. Nonetheless, other issues concerning higher total hydrocarbon (THC) and CO emissions, mainly at low load conditions, are found. To minimize this issue, this research paper evaluates, through a new and alternative approach, the effects of different engine control parameters, such as rail pressure, pilot quantity, start of injection and premixed ratio in terms of efficiency and emissions, and compared to the conventional diesel combustion mode. Indeed, for a deeper understanding of the results, a 1-Dimensional spray model is used to model the air-fuel mixing phenomenon in response to the variations of the calibration parameters that condition the subsequent dual-fuel combustion evolution. Specific variation settings, in terms of premixed ratio, injection pressure, pilot quantity and combustion phasing are proposed for further efficiency improvements.

CO <sub>2</sub> Well-to-Wheel Abatement with Plug-In Hybrid Electric Vehicles Running under Low Temperature Combustion Mode with Green Fuels

<div class="section abstract"><div class="htmlview paragraph">Plug-in Hybrid Electric Vehicles (PHEVs) can be considered as the most promising technology to achieve the European CO<sub>2</sub> targets together with a moderate infrastructure modification. However, the real benefits, in terms of CO<sub>2</sub> emissions, depend on a great extent on the energy source (fuel and electricity mix), user responsibility, and vehicle design. Moreover, the electrification of the powertrain does not reduce other emissions as NOx and particulate matter (mainly soot). In the last years, low temperature combustion (LTC) modes as the reactivity controlled compression ignition (RCCI) have shown to achieve ultra-low NOx and soot emissions simultaneously due to the use of two fuels with different reactivity together with high exhaust gas recirculation (EGR) rates. Therefore, the aim of this work is to assess, through numerical simulations fed with experimental results, the effects of different energy sources on the performance and emissions of a series RCCI PHEV. The dual-fuel engine was fueled with diesel as high reactivity fuel and bioethanol as low reactivity fuel. The powertrains are optimized to meet the European homologation legislation (WLTP) for PHEVs. The tailpipe emissions and fuel consumption of the series RCCI PHEV is analyzed and compared to the OEM no-hybrid passenger vehicle running under conventional diesel combustion and RCCI. A life-cycle analysis (LCA) is performed to evaluate the potential of the different energy sources to reduce the overall CO<sub>2</sub> emissions. Different electricity sources are investigated as well as different liquid fuels: e-diesel and bio-ethanol. The series RCCI PHEV technology achieved the tank-to-wheel 50 g/km CO<sub>2</sub> emissions target with medium battery size (13 kWh). In addition, thanks to the RCCI technology, the vehicle is able to meet the Euro 6 NOx and soot limits. The LCA shows that, depending on the fuel source, the total CO<sub>2</sub> reduction benefits variate. Also, the final use and the charging events of the series PHEV have a great impact in this sense.</div></div>

Study on dual fuel combustion in an optical research engine by infrared diagnostics varying methane quantity and engine speed

Dual fuel combustion represents a possible solution for decreasing the emission produced by diesel engine, while maintaining the efficiency rate at comparable values. In this activity, methane and diesel are used for dual fuel combustion. Methane is injected in the intake manifold, when the intake valves are closed; meanwhile the diesel is delivered directly into the cylinder. The aim of this work is to study the effect of increasing methane concentration at two engine speeds (1500 and 2000 rpm, respectively), on the start and evolution of dual fuel combustion in a compression ignition research engine using infrared diagnostics.Infrared diagnostic has the advantage of being not intrusive, it gives a high spatial and temporal resolution of combustion phenomenon and it is able to qualitatively identify the local concentration of chemical species. Infrared camera detects the energy that the target emits as electromagnetic waves from 3 to 5.5 μm wavelength. Hence, no light sources or multiple optical accesses are needed; and commercial fuels can be used because they emit in the infrared as well.In the experiments, two filters are adopted to follow the whole combustion phenomenon from injection of diesel fuel to late combustion phase with high spatial and temporal resolution. Using the band-pass 3.3 μm, qualitative information about fuel vapour distribution and ignition location during low and high temperature heat release has been provided. Moreover, the combustion evolution is investigated by means of the band-pass filter at 4.2 μm, which is the characteristic of the asymmetric stretch of the CO2 molecule. In particular, autoignition and combustion evolution of the DF combustion are investigated increasing premixed ratio of methane. Differences with the conventional diesel combustion are highlighted. Diesel is the driven fuel that manages the autoignition and combustion of the DF mode in the investigated test cases.