Ignition Delay Period Research Articles

A physics-based model for real-time prediction of ignition delays of multi-pulse fuel injections in direct-injection diesel engines

Real-time prediction of in-cylinder combustion parameters is very important for robust combustion control in any internal combustion engine. Very little information is available in the literature for modeling the ignition delay period of multiple injections that occur in modern direct-injection diesel engines. Knowledge of the ignition delay period in diesel engines with multiple injections is of primary interest due to its impact on pressure rise during subsequent combustion, combustion noise and pollutant formation. In this work, a physics-based ignition delay prediction methodology has been proposed by suitably simplifying an approach available in the literature. The time taken by the fuel-spray tip to reach the liquid length is considered as the physical delay period of any particular injection pulse. An equation has been developed for predicting the saturation temperature at this location based on the temperature and pressure at the start of injection. Thus, iterative procedures are avoided, which makes the methodology suitable for real-time engine control. The chemical delay was modeled by assuming a global reaction mechanism while using the Arrhenius-type equation. Experiments were conducted on a fully instrumented state-of-the-art common-rail diesel engine test facility for providing inputs to develop the methodology. The thermodynamic condition before the main injection was obtained by modeling the pilot combustion phase using the Wiebe function. Thus, the ignition delays of both pilot and main injections could be predicted based on rail pressure, injection timing, injection duration, manifold pressure and temperature which are normally used as inputs to the engine control unit. When the methodology was applied to predict the ignition delays in three different common-rail diesel engines, the ignition delays of pilot and main combustion phases could be predicted within an error band of ±25, ±50 and ±80 µs, respectively, without further tuning. This method can hence be used in real-time engine controllers and hardware-in-the-loop systems.

Thermal self-ignition simulation of pyrotechnic composite in different conditions

The combustion and explosion accidents of pyrotechnic composite occur frequently. The study on the thermal hazard of large size of pyrotechnic composite by experiment method is dangerous. It would consume huge manpower and material resources. In this paper, a study was conducted to investigate the thermal hazards of pyrotechnic composite under different ambient temperature, size and packing condition by numerical simulation method. The results show that the thermal hazards of pyrotechnic composite increase with the increase in ambient temperature. The ignition temperature of pyrotechnic composite as the inherent property of pyrotechnic composite is not affected by packing condition and size. In the same conditions, the lower thermal conductivity of packing material is, the lower SADT of pyrotechnic composite is. With the increase in the size of the grain, its SADT decreases and ignition delay period shortens, and the ignition position shifts from the center to the top of the grain with lower thermal conductivity of packing material.

Emission and combustion profile study of unmodified research engine propelled with neat biofuels.

The current work focuses on the experimental investigation to analyze the combustion and emission characteristics of a direct injection diesel engine fueled with neat biodiesel (BD100) and different proportions of cyclohexanol blends as a fuel additive in various volume fractions. Cyclohexanol is dispersed into a neat biodiesel in a volume fraction of 10, 20, and 30vol%. The biodiesel is produced from neem oil by the conventional transesterification process. The experimental results revealed that with the increased cyclohexanol fraction, the combustion was found smooth. The addition of cyclohexanol has a positive influence on various physical and chemical properties of neat biodiesel. The in-cylinder pressure is comparatively low for diesel followed by cyclohexanol and biodiesel blends when compared with neat biodiesel. This is due to shorter ignition delay period. The heat-release rate of neat biodiesel is the highest among all fuels. The overall HC emission of BD70COH30 is 12.19% lower than BD100 and 16.34% lower than diesel. The overall CO2 emission of BD70COH30 is 13.91% higher than BD100 and 19.5% higher than diesel. The overall NOx emission of BD70COH30 is 5.31% lower than BD100 at all load engine operations. The presence of 10, 20, and 30% of cyclohexanol in biodiesel decreased smoke emissions as compared with neat biodiesel and diesel. The overall smoke emission of BD70COH30 is 19.23% lower than BD100 and 25.51% lower than diesel. The overall CO emission of cyclohexanol blended with biodiesel by 30vol% (BD70COH30) is 17% lower than neat biodiesel and 21.8% lower than diesel. Based on the outcome of this study, neem oil biodiesel and cyclohexanol blends can be employed as a potential alternative fuel for existing unmodified diesel engines owing to its lesser emission characteristics.

Combustion and emission characteristics of E85 and diesel blend in conventional diesel engine operating in PPCI mode

To study the possibility of operating a traditional diesel engine as a partially premixed compression ignition engine, E85 created from 85% bioethanol and 15% unleaded Iraqi gasoline blend was used as the main fuel. E85 blend fuel has a low evaporation temperature, large latent heat and low cetane number (CN). Iraqi diesel fuel was used as a pilot fuel to assure ignition. High rate of cooled exhaust gas recirculation was used. The engine performance and emissions, particularly NOx–smoke trade-off, was also investigated. In order to reduce the number of experiments to be performed, the tests were conducted at a speed of 1500 rpm, with changes in the recirculated exhaust gas rate (10%, 30% and 50%) and change in injection timing (20°, 22°, 25°, 28° and 32° BTDC).Practical results showed that a significant improvement could be achieved in the NOx–PM trade-off. The ignition delay period can be increased by using a low-CN fuel accompanied with a low oxygen intake charge. When using the PPCI system, low levels of NOx and PM can be achieved without affecting the brake thermal efficiency of the engine. Smoke can be reduced even when the EGR percentage is increased under a mixed condition. ED10 (90% E85 + 10% diesel) had the largest decline in NOx (84.66%) and smoke (55.8%) compared to diesel.

Effects of Gravity on Ignition and Combustion Characteristics of Externally Heated Polyethylene Film

The objective of this research is to investigate the effects of gravity on the ignition and the combustion characteristics of the Polyethylene (PE) film by outer heating. Combustion experiments of PE film were carried out in a normal gravity field and the microgravity field. In the microgravity experiments, it was carried out in 50 m-class drop facility. Here it can be realized 10− 4G microgravity field in about 2.5-3.0 second. The PE film is heated by the inserted high-temperature chamber. In the experiments, the PE was used film type. The chamber temperature was fixed at 900 K and 1000 K. In the case of microgravity field, the ignition delay period has become about 50 percent shorter than that in the case of the normal gravitational field. In the normal gravity field, since the PE surface layer is cooled by natural convection, the ignition delay period is considered to be longer than that in the microgravity field. The combustion time in the normal gravity was about 0.8 sec. In the microgravity field, the combustion time was more than 2 sec, and it could not be measured during the free fall period.

Development of multi-component surrogates of diesel from indirect coal liquefaction for spray analysis

The aim of this work is to develop surrogates for the diesel from indirect coal liquefaction (DICL) using a model-based surrogate formulation methodology to emulate the fuel chemical and physical properties affecting the spray process and the ignition delay period. The detail compositions and the temperature-dependent physical properties (density, viscosity and surface tension) of DICL were firstly measured in this work to provide required data for the surrogate formulation method. Three surrogates were developed, which consist of six, four and two components (S1, S2 and S3). Surrogates S1 and S2 can well emulate all the temperature-independent and the temperature-dependent properties, while the S3 can only represent a part of these properties, especially the cetane number (CN) and distillation curve of S3 seriously deviate from the experimental data with deviations of −11.1% and 6.24% respectively. The three newly developed surrogates were used to predict the spray characteristics of the real DICL in the conditions with room temperature. Results show that the three surrogates can well reproduce the spray behaviors of the real DICL.

Effect of intake oxygen concentration on diesel–n-butanol blending combustion: An experimental and numerical study at low engine load

The blends of n-butanol and diesel are easy to achieve the premixed low-temperature combustion (PLTC) without larger exhaust gas recirculation (EGR) rate to maintain combustion stability and reduce emissions. Engine experiment and numerical modeling coupled with a new reduced mechanism were used to investigate both combustion and emission characteristics of D100 (pure diesel) and B30 (30% n-butanol and 70% diesel) under different intake oxygen concentrations (IOCs: 21%, 19%, 17%, and 15%). With the decrease in IOC, the maximum heat release rate (HRR) of D100 increased, while the maximum HRR of B30 first increased and then decreased. NOx emissions of two fuels differed slightly and both significantly decreased. Soot emission of D100 increased, while that of B30 first increased and then decreased. Moreover, under the same IOC, soot emission of B30 was less than that of D100. The chemical kinetic analysis shows that the addition of n-butanol consumed a certain amount of OH, slowed down the oxidation of n-heptane and toluene, and finally prolonged the ignition delay period. Additionally, decreasing in IOC suppressed the low-temperature O2-addition reactions of n-heptane and n-butanol to retard the reaction processes, prolonging the ignition delay. The numerical results show that as the decrease in IOC, the combustion rate decreased, the timings taken for the complete consumption of reactants and the formation of important intermediate products (CH2O, CO, H2O2, and OH) as well as soot precursors (C2H2, A1, and A4) were significantly delayed. Besides, the maximum mass fractions of CH2O, CO, and H2O2 increased, while the maximum OH mass fraction decreased. The formation of soot precursors exhibited similar trends, and reached the maximum mass fraction at an IOC of 17%. Specifically, the increase in soot emission of B30 was caused by the decrease in oxidation, while the decrease was mainly induced by the decrease in formation.

Study of performance, combustion and emission characteristics of heterogeneous catalyzed yellow oleander biodiesel on Compression Ignition (CI) engine

ABSTRACTIn this study, yellow oleander biodiesel was produced using a calcium oxide catalyst. The fuel properties of the yellow oleander biodiesel were in the range of ASTM standards. Effects of the yellow oleander biodiesel and its blends (B10, B20, B30, B40 and B100) were investigated at five different loads (0, 25, 50, 75 and 100%) in a single-cylinder CI engine. Comprehensive combustion analysis showed that the starts of injection timings were inadvertently advanced from the system response. The combustion of yellow oleander biodiesel and its blends generally resulted in a shorter ignition delay period for all loads due to earlier combustion timing. The performance, combustion and emission characteristics of yellow oleander biodiesel and its blends were studied. Variation in the engine emissions were recorded using an AVL DIGAS 444 analyzer. The CO and HC emissions were less for biodiesel test blends (except B100) but NOx emissions increased with closer engine performance when compared to diesel.

Impact of increasing methyl branches in aromatic hydrocarbons on diesel engine combustion and emissions

Lignocellulosic materials have been identified as potential carbon–neutral sources of sustainable power production. Catalytic conversion of lignocellulosic biomass results in liquid fuels with a variety of aromatic molecules. This paper investigates the combustion characteristics and exhaust emissions of a series of alkylbenzenes, of varying number of methyl branches on the monocyclic aromatic ring, when combusted in a direct injection, single cylinder, compression-ignition engine. In addition, benzaldehyde (an aldehyde (-CHO) branch on the monocyclic ring) was also tested. All the molecules were blended with heptane in different proportions, up to 60% wt/wt. The tests were conducted at a constant engine speed of 1200 rpm, a fixed engine load 4 bar IMEP, and at two injection modes: constant start of fuel injection at 10 CAD BTDC, and varying fuel injection timing to maintain constant start of fuel combustion at TDC.The results showed that the ignition delay period increased with increasing number of methyl branches on the ring, due to the rapid consumption of OH radicals by the alkylbenzenes for oxidation to stable benzyl radicals. Peak heat release rates, and concurrently NOx emissions, initially increased with increasing methyl branches, but subsequently both decreased as the bulk of heat release occurred further into the expansion stroke with significant thermal energy losses. With the exception of toluene, the number of particles in the engine exhaust increased as the number of methyl branches on the aromatic ring increased, attributable to the formation of thermally stable benzyl radicals.

Combustion chemistry of iso-octane/ethanol blends: Effects on ignition and reaction pathways

This work presents new experimental data on the ignition of iso-octane and ethanol fuel blends, including measurements of pollutant species and precursors, using the University of Michigan Rapid Compression Facility (UM RCF). Ignition delay times were determined from pressure–time histories of ignition experiments for stoichiometric mixtures of iso-octane, ethanol, and 5, 11, 26, 50 and 67% by volume iso-octane and ethanol blends with air. A range of temperatures (900–1080 K) were studied at a pressure of 10 atm. Speciation experiments were performed for pure iso-octane (E0), pure ethanol (E100) and a 50% by volume blend of the two fuels (E50) at 10 atm and ∼930 K. Fast-gas sampling, gas chromatography and mass spectrometry were used to identify and quantify 14 stable intermediate species formed during the ignition delay periods for the three fuels. The measurements of eight stable intermediates: iso-butene (i-C4H8, 2-methyl-1-propene), propene (C3H6), ethanal (CH3CHO), ethene (C2H4), ethane (C2H6), methane (CH4), carbon monoxide (CO), carbon dioxide (CO2) were considered in detail and were used to describe reaction pathways important during iso-octane and ethanol ignition and how they were altered for iso-octane/ethanol blends. Simulations were carried out using a detailed reaction mechanism for gasoline surrogates available in the literature and the agreement with the ignition and speciation experiments was generally excellent (within the experimental uncertainty and expected computational uncertainty) for ignition delay times and for the species time-histories, with a few small discrepancies. The results indicate the reaction pathways of iso-octane and ethanol in the blend develop in parallel with a shared radical pool with no significant fuel-to-fuel interactions.

Numerical evaluation of pilot-ignition technology used for a hydrogen fuelled free piston engine generator

The spark-ignited free-piston hydrogen engine is characterized with relatively slow combustion and low indicated thermal efficiency. This study explored the pilot-ignition technology to the free-piston hydrogen engine and presented a research to evaluate its applicability. An advanced full-cycle operation model which couples with dynamic, combustion and gas exchange was established to iteratively simulate the effect of pilot-ignition technology on a free piston hydrogen engine. The simulated performances were compared with a corresponding spark-ignition situation. Results indicate that compared with the spark-ignition, the pilot-ignition technology can speed the hydrogen fuel combustion in the free-piston engine and enhance the level of isochoric heat release around top dead center, resulting in more indicated work and higher indicated thermal efficiency. The hydrogen engine adopting the pilot-ignition technology features with faster cycle, larger compression ratio, higher generating power, and slightly more NO emission than the spark-ignition situation. Moreover, the pilot-ignition technology also brings about longer ignition delay and shorter rapid combustion period for the hydrogen engine. However, the released heat in rapid combustion period is significantly more than the spark-ignition situation, which makes that the hydrogen engine operates with larger peak combustion pressure and temperature, and the peak values appear earlier and last shorter.

Experimental characterisation of a diesel engine running on polypropylene oils produced at different pyrolysis temperatures

Polypropylene is the most common type of plastic found in municipal solid waste. The production of polypropylene is expected to increase due to the widespread utilization in daily life, resulting in even higher amounts of polypropylene waste. Sending this plastic to landfill not only exacerbates environmental problems, but also results in energy loss due to the elevated energy content of polypropylene. Pyrolysis is a process that can effectively convert polypropylene waste into fuel, which can then be used to generate power and heat. In the present study, the effect of the pyrolysis temperature on the pyrolysis of polypropylene was investigated, while the oils produced at 700 °C (PP700) and 900 °C (PP900) were used to fuel a four cylinder diesel engine. The engine’s combustion, performance, and emission characteristics were analysed and compared to diesel operation. The results showed that both PP700 and PP900 enabled stable engine operation, with PP900 performing slightly better in terms of efficiency and emissions. However, PP700 and PP900 were found to have longer ignition delay periods, longer combustion periods, lower brake thermal efficiencies, higher NOX, UHC and CO emissions, and lower CO2 emissions in comparison to diesel operation. Nonetheless, the addition of a small quantity of diesel improved the overall performance of the oil blends, resulting in comparable results to diesel in the case of PP900.

Experimental and numerical assessment of ignition delay period for pure diesel and biodiesel B20

The ignition delay period for a compression ignition engine fueled alternatively with pure diesel and with biodiesel B20 has been experimentally and numerically investigated. The engine was operated under full load conditions for two speeds, 1400 rpm speed for maximum brake torque and 2400 rpm speed for maximum brake power. Different parameters suggested as important to define the start of combustion have been considered before the acceptance of a certain evaluation technique of ignition delay. Correlations between these parameters were analyzed and concluded about the best method to identify the start of combustion. The experimental results were further compared with the ignition delay predicted by some correlations. The results showed that the determined ignition delays are in good agreement with those of the Arrhenius type expressions for pure diesel fuel, while for biodiesel B20 the correlation results are significantly different than the experimental results.

Study on the effect of exhaust gas-based fuel preheating device on ethanol–diesel blends operation in a compression ignition engine

Rapid depletion of fossil fuels and stringent emission regulations compel the scientific community to search for alternative energy sources for the internal combustion engines. Among many alternative biofuels, ethanol is getting worldwide attention for compression ignition engine either in the form of partial substitute or complete replacement for diesel fuel. Ethanol fuel has certain undesirable properties like poor flammability limit which results in cold starting issues and higher hydrocarbon emission which restricts their use in compression ignition engine. This issue can be easily overcome by preheating of ethanol fuel before it gets admitted inside the engine cylinder. In the present study, a standard preheating device is designed and fabricated in accordance with engine specifications and simulations were carried out under various operating conditions to evaluate its performance. Furthermore, experimental investigations were carried out in a compression ignition engine fueled with ethanol blends of 20 and 30% with diesel by volume and the fuel blends were preheated using burned exhaust gases. In addition, a comparative study has been carried out for preheated and non-preheated blends of E20 (20% of ethanol and 80% of diesel) and E30 with baseline diesel. The experimental results show that the preheated E20 (20% of ethanol and 80% of diesel) blend has higher brake thermal efficiency of 36.28% with a significant reduction in brake specific fuel consumption when compared with all the other blends. Moreover, the preheated E20 blend reduces the carbon monoxide, unburned hydrocarbon and smoke emissions by 49, 48 and 10%, respectively. However, the NOx emission is increased by 6% as compared to the non-preheating effect. It is also noted that the preheating of ethanol blends produced better combustion results with a significant reduction in the ignition delay period. Hence, it can be concluded that the ethanol fuel can be effectively used in a diesel engine by means of preheating using exhaust gases and could be a viable option for diesel engine applications.

Prediction of thermal explosion parameters for energetic materials on the basis of thermal analysis data

Results obtained in calculations of thermal ignition delay periods in a wide temperature range are in good agreement with published data for octogene samples in the form of a sphere 12.7 mm in diameter and cylindrical NEPE propellant samples with diameters of 20 to 80 mm. The kinetic parameters of the thermal decomposition of materials, used in the calculations, were obtained by the DSC method with the use of hermetically sealed crucibles and crucibles with perforated covers under a nitrogen pressure of 10 MPa at heating rates of 0.1 to 1.0 deg min–1.

Multi-Walled Carbon Nanotubes (MWCNTs) bonded with Ferrocene particles as ignition agents for air-fuel mixtures

The potentials and characteristics of a new ignition system for air-fuel mixtures are discussed. This ignition method (referred to as photo-thermal ignition) is based on light exposure of Multi-Walled Carbon Nanotubes (MWCNTs), bonded with other nano-Structured Materials (nSMs), (collectively referred here as “nanoignition agent”), using a low-consumption camera flash. Here, Ferrocene, an organometallic compound, was used as the nSMs.Results from, and benefits of, this new ignition method are compared with a conventional spark-plug-initiated ignition used in automotive engines.The main objective of this research is to demonstrate ignition feasibility of mixtures of both gaseous and liquid fuels with air under high pressures using the photo-thermal ignition (PTI) phenomenon. Specifically, the ignition and subsequent combustion characteristics of gaseous air-fuel mixtures at different air-fuel ratios were investigated by means of light exposures of nano-ignition agents (nIAs) after they are mixed with air-fuel mixtures.Analysis of the acquired data showed that for the range of air-fuel ratios tested, the photo-thermal ignition with a flash lamp resulted in a higher peak chamber pressure when compared to those obtained with a conventional spark ignition system. Heat release rate analysis showed that shorter ignition delays and total combustion durations for the Photo-thermal ignition are achieved. Comparative percent reduction of these values for photo-ignition ranges from 20% to 50% for LPG and methane, whereas values up to 70% were observed for the hydrogen. The positive impact of the photo-thermal ignition appears to be primarily at the ignition delay period of the combustion. With liquid fuels, photo-thermal ignition was capable to ignite mixtures as lean as a relative air-fuel ratio of 2.7 while the spark ignition was incapable to initiate combustion. Additionally, tests with the liquid gasoline injection highlighted that the combustion process with a higher “residence mixing time” exhibited higher peak pressures and shorter ignition delay times.High-speed camera images were used to capture images of the light emission during the combustion process in visible range, allowing investigation of the ignition processes. In particular, the results showed that the photo-thermal ignition process of the air-fuel mixtures with nano-ignition agents led to a spatially-distributed ignition followed by a faster consumption of the air-fuel mixture with no evidence of any discernible flame front formation or propagation.

Performance and combustion characteristics of a novel crank-rocker engine

The performance and combustion characteristics of a novel internal combustion engine, called the crank-rocker, have been investigated experimentally. The engine specifications are gasoline-port injection, four-stroke, spark-ignition, and single-curved cylinder. The ignition timing was initially set at 8.60 CA BTDC, 1800 rpm based on a small conventional engine. The equivalence ratio, lambda (λ) was varied at rich, stoichiometric, and lean conditions. The entire tests were performed at six different engine speeds of 1800, 2000, 2200, 2400, 2600 and 2800 rpm, with each one operating at wide open throttle. The performance data such as indicated torque, indicated power, indicated specific fuel consumption, and indicated thermal efficiency were calculated. The combustion characteristics such as cylinder pressure, mass fraction burned, heat release rate, P-V diagram, and indicated mean effective pressure were also determined. The results obtained from the crank-rocker engine were compared with the experimental results obtained from the conventional engine (benchmark engine). The results showed that the indicated torque, power and thermal efficiency of crank-rocker engine is higher than normal slidercrank engine. The indicated torque and power increased by about 6.28 %, while the indicated specific fuel consumption is lower by 4.69 %. In general, the engine has similar indicated performance characteristics to the conventional engine, but the combustion characteristics differ because the peak values of the combustion pressure and heat release occur at higher crank angle ATDC. This was found to be due to the dwelling of piston at TDC. The combustion rate and mixture of the novel crank-rocker engine burned faster, resulting in shorter combustion duration and ignition delay period than the conventional slider-crank engine.

The effect of hydrogen injection parameters on the quality of hydrogen–air mixture formation for a PFI hydrogen internal combustion engine

To research the quality of the hydrogen–air mixture formation and the combustion characteristics of the hydrogen fueled engine under different hydrogen injection timings, nozzle hole positions and nozzle hole diameter, a three-dimensional simulation model for a PFI hydrogen internal combustion engine with the inlet, outlet, valves and cylinder was established using AVL Fire software. In the maximum torque condition, research focused on the variation law of the total hydrogen mass in the cylinder and inlet and the space distribution characteristics and variation law of velocity field, concentration field and turbulent kinetic energy under different hydrogen injection parameters (injection timings, nozzle hole positions and nozzle hole area) in order to reveal the influence of these parameters on hydrogen–air mixture formation process. Then the formation quality of hydrogen–air mixture was comprehensively evaluated according to the mixture uniformity coefficient, the remnant hydrogen percentage in the inlet and restraining abnormal combustion (such as preignition and backfire). The results showed that the three hydrogen injection parameters have important influence on the forming quality of hydrogen–air mixture and combustion state. The reasonable choice of the nozzle hole position of hydrogen, nozzle hole diameter and the hydrogen injection time can improve the uniformity of the hydrogen–air mixing in the cylinder of the hydrogen internal combustion engine, and the combustion heat release reaction is more reasonable. At the end of the compression stroke, the equivalence ratio uniform coefficient increased at first and then decreased with the beginning of the hydrogen injection. When hydrogen injection starting point was with 410–430°CA, equivalence ratio uniform coefficient was larger, and ignition delay period was shorter so that the combustion performance index was also good. And remnant hydrogen percentage in the inlet was less, high concentration of mixed gas in the vicinity of the inlet valve also gathered less, thus suppressing the preignition and backfire. With the increase of the distance between the nozzle and the inlet valve, the selection of the hydrogen injection period is narrowed, and the optimum hydrogen injection time was also ahead of time. The results also showed that it was favorable for the formation of uniform mixing gas when the nozzle hole diameter was 4 mm.

Experimental investigation on performance, combustion and emission characteristics of a common-rail diesel engine fueled with polyoxymethylene dimethyl ethers-diesel blends

Polyoxymethylene dimethyl ethers (PODE) was blended with diesel fuel at volume ratio of 10%, 20% and 30% in the preparation of PODE-diesel blend fuels (marked as P10, P20 and P30). The volatility and oxidation characteristics of blend fuels, and the thermal parameters were analyzed using thermogravimetric method and Coast-Redfern integral method respectively. Also, the effects of PODE-diesel blends on the performance, combustion and emission characteristics were carried out on a 4-cylinder turbocharged intercooled common-rail diesel engine. The results show that P10, P20 and P30 have good stability at room temperature, and also the kinematic viscosity of PODE-diesel blends gradually decreases with increasing PODE blending ratio and temperature. Also with the increase of the blending ratio of PODE, the activation energy of blend fuels decreases and the comprehensive combustion index improves. When the diesel engine is fueled with PODE-diesel blends, the ignition delay period is shortened, shifting the rate of heat release and the rate of pressure rise curves forward. This increment in PODE blending ratio increases the maximum in-cylinder pressure and improves the brake thermal efficiency. The blend fuel has little impact on NOX emissions, however, it can significantly improve HC, CO and smoke emissions. Compared with pure diesel fuel, the smoke emissions of P10, P20 and P30 at full load are reduced by 27.6%, 41.5% and 47.6%, respectively. PODE-diesel blends therefore could reduce particle number concentration and particle mass concentration in diesel exhausts, shifting the distribution peak to small particle sizes. Compared with pure diesel fuel, the peak number concentration of accumulation-mode particles (50nm<Dp<1000nm) of P10, P20 and P30 decrease by 15.97%, 32.28% and 43.79%, respectively. This indicates that PODE as one of the emerging alternative fuels has the potential to achieve high efficient and clean combustion for diesel engines.

The utilisation of oils produced from plastic waste at different pyrolysis temperatures in a DI diesel engine

Chemical recycling is an attractive way to address the explosive growth of plastic waste and disposal problems. Pyrolysis is a chemical recycling process that can convert plastics into high quality oil, which can then be utilised in internal combustion engines for power and heat generation. The aim of the present work is to evaluate the potential of using oils that have been derived from the pyrolysis of plastics at different temperatures in diesel engines. The produced oils were analysed and found to have similar properties to diesel fuel. The plastic pyrolysis oils were then tested in a four-cylinder direct injection diesel engine, and their combustion, performance and emission characteristics analysed and compared to mineral diesel. The engine was found to perform better on the pyrolysis oils at higher loads. The pyrolysis temperature had a significant effect, as the oil produced at a lower temperature presented higher brake thermal efficiency and shorter ignition delay period at all loads. This oil also produced lower NOX, UHC, CO and CO2 emissions than the oil produced at a higher temperature, although diesel emissions were lower.