Start Of Combustion Research Articles

Optimization of homogeneous charge compression ignition combustion in a light-duty diesel engine operated using ethyl acetate-gasoline blends

The low temperature combustion mode of homogeneous charge compression ignition eliminates particulate matter and oxides of nitrogen (NO x) emissions trade-off that prevails in high-temperature, diffusion-controlled conventional diesel combustion (CDC). In the present research, the significant challenge of narrow operating load range that hinders the commercial implementation of light-duty HCCI engines was overcome by employing ethyl acetate-gasoline blends. The gasoline concentration in test fuels was reduced in 10% decrements, from 84% to 24%, to replace it with ethyl acetate. The use of ethyl acetate, a renewable fuel, can help solve the energy crisis due to the rapid depletion of fossil fuels. An ignition improver was blended in the test fuels in a predetermined amount of 6% so that combustion stability was not hampered at lower loads. Parametric investigations were conducted to study the effect of progressively increasing ethyl acetate in test fuels on HCCI combustion, performance, and emissions. The machine learning tool of artificial neural network was implemented to learn the behavior of the test engine, considering load and fuel composition as input variables. The feedforward artificial neural network models were developed to predict the start of combustion, combustion phasing, indicated thermal efficiency, and emissions of carbon monoxide, soot, NO x, and unburned hydrocarbon (HC). A multi-objective optimization was performed to arrive at the best operating condition by integrating artificial neural network models with the genetic algorithm. All the developed artificial neural network models could predict responses with acceptable accuracy. The genetic algorithm indicated that the optimum point of the operation was at 80% load and 65% ethyl acetate in the test fuels. Experiments were conducted to validate the optimal HCCI conditions that resulted in 27% higher indicated thermal efficiency, 54% lower HC+NOx, and 99% lower soot emissions than CDC. Overall, the present study demonstrated the benefits of considering ethyl acetate as a fuel to improve HCCI engine metrics of off-road diesel engines.

Experimental study on effects of compression ratio, ignition timing, and hydrogen addition on ignition delay and combustion rate of heavy-duty truck engine fueled with liquefied methane

ABSTRACT Natural gas (NG) is a potential alternative fuel for carbon neutral and has been received increasing attentions on its combustion behaviors in engine. However, there is little systematic quantitative investigation on the combustion characteristic of purified NG (methane) engine. In this study, the sweeping tests for compression ratio (CR), ignition timing, and hydrogen addition were conducted on a heavy-duty truck liquid methane engine, and the influence factors of ignition delay and combustion rate at each stage were quantitatively investigated. Some new findings and interesting conclusions were obtained. Overall, CR especially the higher CR has small effect on the ignition delay of methane engine (less than 2 deg). Under all the conditions discussed, the ignition delay almost linearly increases with the advance of ignition timing, resulting in the slight advance of start of combustion (SOC). Compared with ignition timing, hydrogen addition has larger effect on SOC since it reduces ignition delay largely (up to 7.3 deg at 1400rpm). By increasing hydrogen addition, the CA10–50 shortens slightly while CA50–90 elongates largely, resulting in a rising trend in CA10–90 finally. All these have extended the research on methane engine and are useful to improve its combustion performance.

Accelerometer-based SOC estimation methodology for combustion control applied to Gasoline Compression Ignition

The European Community’s recent decision to suspend the marketing of cars with conventional fossil-fueled internal combustion engines from 2035 requires new solutions, based on carbon-neutral technologies, that ensure equivalent performances in terms of reliability, trip autonomy, refueling times and end-of-life disposal of components compared to those of current gasoline or diesel cars. The use of bio-fuels and hydrogen, which can be obtained by renewable energy sources, coupled with high-efficiency combustion methodologies might allow to reach the carbon neutrality of transports (net-zero carbon dioxide emissions) even using the well-known internal combustion engine technology. Bearing this in mind, experiments were carried out on compression ignited engines running on gasoline (GCI) with a high thermal efficiency which, in the future, could be easily adapted to run on a bio-fuel. Despite the well-reported benefits of GCI engines in terms of efficiency and pollutant emissions, combustion instability hinders the diffusion of these engines for industrial applications. A possible solution to stabilize GCI combustion is the use of multiple injections strategies, typically composed by 2 early injected fuel jests followed by the main injection. The heat released by the combustion of the earlier fuel jets allows to reduce the ignition delay of the main injection, directly affecting both delivered torque and center of combustion. As a result, to properly manage GCI engines, a stable and reliable combustion of the pre-injections is mandatory. In this paper, an estimation methodology of the start of combustion (SOC) position, based on the analysis of the signal coming from an accelerometer sensor mounted on the engine block, is presented (the optimal sensor positioning is also discussed). A strong correlation between the SOC calculated from the accelerometer and that obtained from the analysis of the rate of heat release (RoHR) was identified. As a result, the estimated SOC could be used to feedback an adaptive closed-loop combustion control algorithm, suitable to improve the stability of the whole combustion process.

Effect of Hydrogen Enhancement on Natural Flame Luminosity of Tri-Fuel Combustion in an Optical Engine

A novel combustion mode, namely tri-fuel (TF) combustion using a diesel pilot to ignite the premixed methane–hydrogen–air (CH4–H2–air) mixtures, was experimentally investigated under various H2 fractions (0%, 10%, 20%, 40%, 60%) and ultra-lean conditions (equivalence ratio of φ= 0.5). The overarching objective is to evaluate the effect of H2 fraction on flame characteristics and engine performance. To visualize the effect of H2 fraction on the combustion process and flame characteristics, a high-speed color camera (Photron SA-Z) was employed for natural flame luminosity (NFL) imaging to visualize the instantaneous TF combustion process. The engine performance, flame characteristics, and flame stability are characterized based on cylinder pressure and color natural flame images. Both pressure-based and optical imaging-based analyses indicate that adding H2 into the CH4–air mixture can dramatically improve engine performance, such as combustion efficiency, flame speed, and flame stability. The visualization results of NFL show that the addition of H2 promotes the high-temperature reaction, which exhibits a brighter bluish flame during the start of combustion and main combustion, however, a brighter orangish flame during the end of combustion. Since the combustion is ultra-lean, increasing the H2 concentration in the CH4–air mixture dramatically improves the flame propagation, which might reduce the CH4 slip. However, higher H2 concentration in the CH4–air mixture might lead to a high-temperature reaction that sequentially promotes soot emissions, which emit a bright yellowish flame.

Operating Range, Performance and Emissions of an HCCI Engine Fueled with Fusel Oil/Diethyl Ether: An Experimental Study

The main disadvantages of HCCI engines are the knocking tendency at high engine loads, the challenge of the start of the combustion, control of the combustion phase, and the narrow operating range. In this study, we aimed to control the combustion processes in HCCI engines and to expand their working range by improving the fuel properties of fusel oil by the addition of diethyl ether. Thus, the variations in the in-cylinder pressure, rate of heat release, indicated mean effective pressure, start of combustion, combustion duration, CA50, indicated thermal efficiency, mean pressure rise rate, hydrocarbon and carbon monoxide emissions were investigated. It was observed that the in-cylinder pressure and rate of heat release were taken into advance and the test engine could be operated for a wider range by increasing the diethyl ether ratio in the blend. The indicated mean effective pressure increased by 67.5% with DEE40 fuel compared to the DEE80. Under the same operating conditions, HC and CO emissions decreased by 41.6% and 56.2%, in use of DEE40. Furthermore, the highest indicated thermal efficiency was obtained as 42.5% with DEE60 fuel. Maximum hydrocarbon and carbon monoxide emissions were observed with DEE80 fuel as 0.532% and 549 ppm, respectively.

Utilization of multiwalled carbon nanotubes (MWCNT) additive in HCCI engine to widen operating range

Homogenous charge compression ignition (HCCI) combustion mode is a promising technology for the future of internal combustion engines because of its high thermal efficiency. However, HCCI engines have limited stable operating range which is a major drawback. Nanoparticles usage as fuel additive provides improvement of combustion characteristics of internal combustion engines. The objective of this study is to enlarge operating range of HCCI engine. For this purpose, the effects of multiwalled carbon nanotubes (MWCNT) on combustion characteristics of an HCCI engine were scrutinized. The effects of MWCNT on engine operating range, combustion parameters, and HC and CO emissions were determined. The maximum operating range was obtained with 75 % n-heptane, 25 % ethanol, and 100 ppm MWCNT mixture. Compared to 75 % n-heptane and 25 % ethanol mixture, 75 % n-heptane, 25 % ethanol, and 100 ppm MWCNT mixture increased the operating range of engine 112 %. Furthermore, in-cylinder pressure, heat release rate, indicated thermal efficiency, and maximum pressure rise rate were increased with use of MWCNT additive. Start of combustion and 50 % heat release location was shifted to earlier crank angles. Combustion duration was shortened. HC and CO emissions were also decreased.

IMPROVMENT OF ENVIRONMENTAL PERFORMANCE TWO-STROKE DIESEL DURING OPERATION

The development of world shipping is taking place in the context of ever-increasing requirements to reduce the concentrations of toxic components of gaseous combustion products of hydrocarbon fuels. Concentration limits for these substances are regulated in accordance with Appendix VI of the MARPOL 73/78 Convention. Among the controlled components of diesel exhaust gases, nitrogen oxides are the most dangerous for humans and environment. However, a decrease in the content of nitrogen oxides is inevitably associated with limitations on the maximum cycle temperature, that is, thermal efficiency, and hence with a deterioration in the fuel efficiency of the engine. At the moment, in order to reduce emissions of nitrogen oxides by large transport diesel engines, the most widely used is the recirculation of exhaust gases into the air receiver. A significant disadvantage of using this scheme is the need for cooling the exhaust gases and their additional purification, which leads to an increase in the weight and size characteristics of the system and to its rise in price. Therefore, to reduce its cost, it seems logical to combine exhaust gas recirculation with other ways to reduce nitrogen oxide emissions. For engines in operation, one of these methods is to change the angle of fuel injection. It can be assumed that the later the fuel is injected into the cylinder, the lower the temperature of the air charge will be and, accordingly, the lower the maximum combustion temperature, and hence the amount of nitrogen oxides. The calculation of nitrogen oxide emissions was simulated for the main engine MAN-B&W 7S50MC-C installed on the vessel "LILA SHANGHAI". Initially, the model created using the AVL-BOOST package was verified based on the available indexing results. After verification, the calculation of emissions of nitrogen oxides NOx was made with a variation in the angle of the start of fuel combustion at the nominal mode. The composition of the gases in the receiver was taken unchanged. As the fuel combustion start angle shifted further from the TDC, deterioration in fuel efficiency and a drop in cylinder power were observed, while reducing the mass of emitted nitrogen oxides NOx. However, it can be said that the environmental friendliness of an engine improves much faster than its fuel and power characteristics deteriorate. The above calculations show that for engines already in operation, changing the fuel injection angle makes it possible to reduce nitrogen oxide emissions. Therefore, this approach can be combined without much difficulty with other methods, thus reducing the cost of environmental improvement of the engine.

Simulation study on effects of EGR ratio and compression ratio on combustion and emission characteristics of PODE/methanol RCCI engine

In order to solve the problems of combustion instability and emission deterioration of reactivity controlled compression ignition (RCCI) engine under high load, the in-cylinder combustion model of polyoxymethylene dimethyl ethers (PODE)/methanol dual-fuel RCCI engine was constructed by CONVERGE software coupling with chemical reaction mechanism, and the influence mechanism of exhaust gas recirculation (EGR) ratio and compression ratio (CR) on engine performance, in-cylinder combustion and emission characteristics of PODE/methanol RCCI mode was systematically studied. Results show that with the increase of EGR ratio, the combustion phase of RCCI mode is gradually delayed, the ignition delay and combustion duration are extended, the CA50 phase is gradually delayed, the combustion temperature decreases, the mixture distribution becomes more uniform, and the combustion process becomes smoother. When the EGR ratio increases from 0 % to 30 %, NOx production is reduced by 47.3 %, ringing intensity (RI) and maximum pressure rise rate (MPRR) decreases by 1.31 MW/m2 and 0.37 MPa/°CA respectively, and brake thermal efficiency (BTE) decreases from 45.45 % to 43.19 %. With the reduction of CR, the combustion start point is gradually postponed, the peak heat release rate and combustion temperature continuously decrease, and both IMEP and BTE show a downward trend. The variation of CR breaks the trade-off relationship between NOx and soot, and improves combustion stability, but it is also limited by the BTE reduction. When the CR decreases from 17.5 to 15.5, NOx and soot production are reduced by 28.58 % and 20.1 %, RI and MPRR are reduced by 1.26 MW/m2 and 0.7 MPa/°CA respectively, and BTE decreases from 45.45 % to 44.52 %. Therefore, the CR of 16.5 is more suitable for stable operation of PODE/methanol dual-fuel RCCI engine at high load.

Effect of ignition timing on the combustion process of a port injection free piston linear generator: A system level multi-physics coupling method

Free piston linear generators (FPLGs) have the advantages of high power density, high compactness and flexible compression ratio, rendering FPLGs as potential power sources in pure electric range extension, hybrid power and various outdoor power fields. In the present study, the influence of ignition timing on the performance of a dual-piston dual-cylinder free-piston engine generator was experimentally investigated. A FPLG multi-physics coupled simulation-experimental bench was specially developed, and the effect of ignition timing on the engine performance was investigated through the three-dimensional numerical simulation method. The simulation results showed that with the increase of spark advance, both the peak in-cylinder pressure and the heat release rate raised, and the maximum peak pressure could reach over 30 bar under given scenarios. With the increase of ignition timing, the start of combustion was significantly advanced, and the maximum advance in combustion initiation was about 19°ECA over the investigated engine speeds. When the ignition timing ranges were −35°ECA ∼ -20°ECA, the combustion durations were roughly varied between 20°ECA ∼ 30°ECA. At the specified engine speed, when the ignition timing was earlier than − 20°ECA, the indicated power and indicated thermal efficiency were not sensitive to ignition timing. As the engine speed and spark advance increased,the NOx mass fraction in the combustion process were raised. The heat transfer loss decreased with the retarding of the ignition timing, and it increased as the engine speed decreased.

Thermofluids analysis of combustion, emissions, and energy in a biodiesel (C11H22O2) / natural gas heavy-duty engine with RCCI mode (Part II: Fuel injection time/ Fuel injection rate)

• With the same energy production by diesel and biodiesel, the biodiesel combustion start earlier because of more oxygen content. • The biodiesel fuel (C11H22O2) used in this research is a new fuel derived from algae and is being simulated for the first time at this level for heavy-duty biodiesel engine. • The maximum pressure for biodiesel fuel is approximately equal to 9.12 MPa and for diesel fuel is equal to 8.9 MPa. • By advancing the injection start time from 16 to 8 crank angle degrees, the mass of soot is facing a decreasing trend. Among the measures that improve the combustion process and reduce emissions in the design of dual-fuel engines is the use of the RCCI combustion strategy. This paper attempts to investigate the effects of biodiesel and diesel fuels, fuel injection time, and fuel injection rate in the RCCI combustion mode. In this study, using CONVERGE CFD commercial software and SAGE combustion model for the simulation. Accordingly, the geometry of a biodiesel (C 11 H 22 O 2 ) / natural gas dual-fuel engine (Caterpillar 3401E) was exploited for experimental tests and numerical simulations. Results show that: The pressure inside the combustion chamber is especially greater from -12° to +10° crank angle for biodiesel, in fact, the maximum pressure for biodiesel fuel is approximately equal to 9.12 MPa and for diesel fuel is equal to 8.9 MPa. The mass of HC emissions for the two fuels is almost equal, but the mass of CO emissions for biodiesel is higher than diesel. By reducing the duration of fuel injection from 16° to 8° crank angle, the mass of soot is facing a decreasing trend, and this amount lowers from 0.065 to 0.00086 mg. Moreover, the indicated mean effective pressure (IMEP) and production work have increased from Case A (8 and 16 mg biodiesel in the first and second injection) to C (16 and 8 mg biodiesel in the first and second injection), and the knocking rate is reached from 3.4 to 6.6.

Modelling of hydrogen-blended dual-fuel combustion using flamelet-generated manifold and preferential diffusion effects

In the present study, Reynolds-Averaged Navier-Stokes simulations together with a novel flamelet generated manifold (FGM) hybrid combustion model incorporating preferential diffusion effects is utilised for the investigation of a hydrogen-blended diesel-hydrogen dual-fuel engine combustion process with high hydrogen energy share. The FGM hybrid combustion model was developed by coupling laminar flamelet databases obtained from diffusion flamelets and premixed flamelets. The model employed three control variables, namely, mixture fraction, reaction progress variable and enthalpy. The preferential diffusion effects were included in the laminar flamelet calculations and in the diffusion terms in the transport equations of the control variables. The resulting model is then validated against an experimental diesel-hydrogen dual-fuel combustion engine. The results show that the FGM hybrid combustion model incorporating preferential diffusion effects in the flame chemistry and transport equations yields better predictions with good accuracy for the in-cylinder characteristics. The inclusion of preferential diffusion effects in the flame chemistry and transport equations was found to predict well several characteristics of the diesel-hydrogen dual-fuel combustion process: 1) ignition delay, 2) start and end of combustion, 3) faster flame propagation and quicker burning rate of hydrogen, 4) high temperature combustion due to highly reactive nature of hydrogen radicals, 5) peak values of the heat release rate due to high temperature combustion of the partially premixed pilot fuel spray with entrained hydrogen/air and then background hydrogen-air premixed mixture. The comparison between diesel-hydrogen dual-fuel combustion and diesel only combustion shows early start of combustion, longer ignition delay time, higher flame temperature and NOx emissions for dual-fuel combustion compared to diesel only combustion.

Effect of mixed nonionic surfactants on microemulsion phase boundary, fuel property, and engine performance of biofuels

Microemulsion biofuels can become one of alternative biodiesels using suitable nonionic surfactants and cosurfactant to emulsify vegetable oil and ethanol with the appropriate formulae. Without the further chemical improvement, the low volatility and high viscosity because of triglycerides in vegetable oil can cause a serious problem in engine operation. This work proposed a systematic investigation of microemulsion biofuel prepared from rice bran oil and ethanol using mixed nonionic surfactant systems (Dehydol LS7, Tween 80, and Span 80) as surfactant (S) and 1-octanol as a cosurfactant (C) at molar ratio of 1:30. Microemulsion phase behaviors can be examined through the ternary phase diagram of rice bran oil, ethanol, and S:C. It was observed that Dehydol LS 7 was poor in solubilization of rice bran oil and ethanol because of their preference in hydrophilic compounds rather than lipophilic compounds. Introduction of Tween 80 or Span 80 into the biofuels using Dehydol LS 7 enhanced the solubilization of these systems as the extent of single-phase boundary was significantly enlarged because of the hydrophilic–lipophilic balance of the mixture and chemical structure of surfactants. The fuel properties of microemulsion biofuel were investigated through kinematic viscosity, specific gravity, flash point, cloud point, pour point, and higher heating value. It was found that mixed surfactant also improved some fuel properties due to additional surfactants contain many oxygenated functional groups, however, some parameters were slightly substandard. The combustion characteristics and exhaust emission were investigated in CI diesel engine. It was observed that the in-cylinder pressure was lower under the combustion of microemulsion fuel mainly due to the high latent heat of vaporization of alcohols. The start of combustion was more retarded with the addition of Span 80, especially at low load condition. It was observed that the significant reduction in nitrogen oxides was achieved with the combustion of microemulsion fuel while unburnt hydrocarbon emissions were higher compared to diesel fuel. The obtained experimental data showed that microemulsion biofuels can be a promising alternative biodiesel although the individual usage in engine was slightly less efficient than commercial diesel fuel.

Prediction of the influence of castor oil–ethanol–diesel​ blends on single-cylinder diesel engine characteristics using generalized regression neural networks (GRNNs)

With some inferior fuel properties such as cetane number, flash point and calorific value, in this study the ethanol–diesel blend was improved through the use of neat castor oil. According to a preliminary study on blending stability and lubricity, a fuel blend was formulated with 10% ethanol, 10% castor oil and 80% diesel fuel (D80E10C10) which was selected to test in the diesel engine. The generalized regression neural network (GRNNs), which is one of the artificial intelligence algorithms that is suitable for a small data set, was applied to create a model for predicting the influence of castor oil on the characteristics of the diesel engine fueled with an ethanol–diesel blend. The experimental results of fuel properties were firstly analyzed and revealed that the presence of 10% castor oil can improve the defective fuel properties of ethanol–diesel to keep them under the limitations of the diesel fuel specification. A lower thermal efficiency was obtained with the combustion of the castor oil blend. A higher peak of in-cylinder pressure and the earlier start of combustion was achieved with increasing engine operating load and compression ratio. A lower peak of heat release rate was attained with the combustion of the castor oil blend. Hydrocarbons and carbon monoxide were increased with the castor oil blend, while oxides of nitrogen were decreased and no significant change in smoke emissions was found with respect to diesel fuel. Subsequently, the results of the prediction model concluded that the response surface methodology was a good method to optimize the smoothing parameter of the GRNNs model in the case of multi-output factors with different levels of importance. The GRNNs model was achieved with relatively high performance to predict BSFC, thermal efficiency, NOx, HC, CO and smoke emissions, with mean absolute percentage error (MAPE) values in the range of 1.562%–8.181% and coefficient of determination (R2) in the range of 0.708-0.993.

Fast detection of compartment fires under different heating conditions of materials

The paper presents experimental findings for the characteristics of equipment activation for the detection of pyrolysis and flame combustion under different heating conditions of materials. Class A model fires in the experiments involved a group of typical indoor combustible materials (wood, linoleum, cardboard, paper). Three most common causes of fires were reproduced: careless handling of fire (open flame), unsafe operation of heating equipment and electrical short circuits. To identify the characteristics of pyrolysis and ignition (i.e., stages preceding a fire), an automated system featuring fire (heat, smoke, flame) detectors, contact and non-contact temperature measurement instruments, a gas analysis system (CO, CO2, O2) and video recording equipment was used. Following the experiments, the scope of technical equipment (smoke, heat and flame detectors, gas analytical sensors, video recording systems) for the detection of pyrolysis of combustible materials and flame combustion start was determined. The most efficient combinations of equipment, necessary and sufficient for the identification of pyrolysis of combustible materials, were established for different fire causes. The values of the efficiency coefficients of fire detectors are calculated. It is shown that their values for different types of detectors can vary in a wide range (0.1–0.9). Recommendations were made on upgrading the existing fire prevention systems in buildings and creating new automated ones, allowing faster identification of an incipient fire, considering the specific character of the fire hazard source: open flame, heating equipment, electrical overload.

Development of a Control-Oriented Ignition Delay Model for GCI Combustion

Increasingly stringent pollutant emission limits and CO2 reduction policies are forcing the automotive industry toward cleaner and decarbonized mobility. The goal is to achieve carbon neutrality within 2050 and limit global warming to 2 °C (possibly 1.5 °C) with respect to pre-industrial levels as stated in both the European Green Deal and the Paris Agreement and further reiterated at the COP26. With the aim of simultaneously reducing both pollutants and CO2 emissions, a large amount of research is currently carried out on low-temperature highly efficient combustions (LTC). Among these advanced combustions, one of the most promising is Gasoline Compression Ignition (GCI), based on the spontaneous ignition of a gasoline-like fuel. Nevertheless, despite GCI proving to be effective in reducing both pollutants and CO2 emissions, GCI combustion controllability represents the main challenge that hinders the diffusion of this methodology for transportation. Several works in the literature demonstrated that to properly control GCI combustion, a multiple injections strategy is needed. The rise of pressure and temperature generated by the spontaneous ignition of small amounts of early-injected fuel reduces the ignition delay of the following main injection, responsible for the torque production of the engine. Since the combustion of the pre-injections is chemically driven, the ignition delay might be strongly affected by a slight variation in the engine control parameters and, consequently, lead to misfire or knocking. The goal of this work was to develop a control-oriented ignition delay model suitable to improve the GCI combustion stability through the proper management of the pilot injections. After a thorough analysis of the quantities affecting the ignition delay, this quantity was modeled as a function of both a thermodynamic and a chemical–physical index. The comparison between the measured and modeled ignition delay shows an accuracy compatible with the requirements for control purposes (the average root mean squared error between the measured and estimated start of combustion is close to 1.3 deg), over a wide range of operating conditions. As a result, the presented approach proved to be appropriate for the development of a model-based feed-forward contribution for a closed-loop combustion control strategy.

Effects of isobutanol fraction in diesel–biodiesel blends on combustion, injection, performance and emission parameters

High carbon alcohols such as isobutanol have gained much research interest recently in diesel engines due to their higher mixing stability, lower water retention, higher energy density and higher cetane number compared to low carbon alcohols like ethanol and methanol. Therefore, the effects of increasing isobutanol fractions in diesel–biodiesel blends on combustion, injection, performance and emission parameters were investigated on a common rail diesel engine with two stage injection strategy at different engine speeds and loads. Six test fuels were; pure diesel, binary mixtures of biodiesel and isobutanol with diesel (B20 and I15), ternary blends of isobutanol-diesel–biodiesel (I15B20, I25B20 and I35B20) prepared on mass basis. Results showed that increasing isobutanol fraction in the blends retarded start of combustion (SOC) and decreased cylinder gas pressure and maximum rate of heat release. Ignition delay increased and combustion duration decreased with increasing isobutanol proportion in test fuels. Maximum pressure rise rate of ternary blends slightly increased with increasing load and speed and observed slightly above the knocking limit at 160 Nm and 2100 rpm, having 21.58 % higher value than that of diesel. Increasing isobutanol fraction in ternary blends increased brake specific fuel consumption (BSFC), while providing comparable thermal efficiencies with diesel at medium and high loads, where 4.72 % higher value obtained with I15B20 compared to pure diesel at 160 Nm. Generally, higher isobutanol ratios decreased THC and CO emissions and suppressed cyclic variations at high load. All blends increased NOx emissions compared to diesel, whereas test fuels with high isobutanol content suppressed NOx emissions at low load. Increasing isobutanol ratio in the blends prevented further increase in NOx emissions, while B20 fuel evidently increased NOx emissions at 160 Nm. At high load and 1800 rpm, I35B20 fuel gave optimum results with 3.53 % and 12.66 % lower THC and CO emissions, 2.37 % and 7.27 % higher BTE and NOx, respectively, compared to pure diesel.

Ternary gasoline – Pomegranate peel oil (PPO)- tertiary butyl alcohol (TBA) blend as an enabler to improve the spark-ignited engine performance and emissions

This paper reported a research work that investigated the compatibility of using pomegranate peel oil (PPO) as a substitute for gasoline in a spark-ignition engine. Initially, fuel characterization was performed for the PPO biofuel, and a blend was prepared by blending PPO in gasoline at a ratio of 10:90 by volume. Then, fuel properties were measured for the gasoline, PPO, and its blend. Subsequently, engine experiments were conducted for the blend at different load conditions with constant speed, and the performance, combustion, and emission results of the blend were compared with that of sole gasoline. By analyzing the results, it was found that the brake thermal efficiency of the 10% PPO blended gasoline was reduced by 1.2%, 0.6%, and 1%, at low load, mid load, and full load, respectively, when compared to sole gasoline. Whereas the HC and CO emission of the blend was higher by about 11.7% and 8.3%, respectively, at full load, when compared to that of gasoline. With an intent to improve the performance of the PPO blend, tertiary butyl alcohol (TBA) was blended with the 10% PPO blended gasoline in the volumetric proportion of 5%, 10%, and 15% to form ternary blends. The experimental study revealed that the performance of the PPO blend was enhanced significantly with increasing TBA proportion in the blend. The PPO blend with 15% TBA exhibited the highest BTE of 25.1%, which was 1.6% higher than gasoline at full load. The same blend resulted in the HC and CO emissions that were 9.2% and 9.6% lesser than gasoline, respectively, whereas NO emission was 7.6% higher than gasoline, at full load condition. The combustion analysis revealed that the start of combustion was delayed, with peak pressure and heat release rate being the maximum for ternary blends. From this investigation, it can be concluded that the sole gasoline can be replaced by the ternary blend as fuel for SI engine operation without requiring any major engine modification.

The Effect of Ignition Timing on the Emission and Combustion Characteristics for a Hydrogen-Fuelled ORP Engine at Lean-Burn Conditions

The application of hydrogen fuel in ORP engines makes the engine power density much higher than that of a reciprocating engine. This paper investigated the impacts of combustion characteristics, energy loss, and NOx emissions of a hydrogen-fuelled ORP engine by ignition timing over various equivalence ratios using a simulation approach based on FLUENT code without considering experiments. The simulations were conducted under the equivalence ratio of 0.5~0.9 and ignition timing of −20.8~8.3° CA before top dead centre (TDC). The engine was operated under 1000 RPM and wide-open throttle condition which was around the maximum engine torque. The results indicated that significant early ignition of the ORP engine restrained the flame development in combustion chambers due to the special relative positions of ignition systems to combustion chambers. In-cylinder pressure evolutions were insensitive to early ignition. The start of combustion was the earliest over the ignition timing of −17.3° CA for individual equivalence ratios; the correlations of the combustion durations and equivalence ratios were dependent on the ignition timing. Combustion durations were less sensitive to equivalence ratios in the ignition timing range of −14.2~−11.1° CA before TDC. The minimum and maximum heat release rates were 15 J·(°CA)−1 and 22 J·(°CA)−1 over the equivalence ratios of 0.5 and 0.9, respectively. Indicated thermal efficiency was higher than 41% for early ignition scenarios, and it was significantly affected by late ignition. Energy loss by cylinder walls and exhaust was in the range of 10~16% and 42~58% of the total fuel energy, respectively. The impacts of equivalence ratios on NOx emission factors were affected by ignition timing.

Time frequency analysis for the evaluation of ignition delay in conventional and PCCI combustion modes

• Time frequency analysis can detect both start of injection and start of combustion. • Time frequency analysis can provide an accurate evaluation of ignition delay in diesel engines. • Combustion development for PCCI and conventional diesel modes is investigated. In-cylinder pressure signal has been widely adopted to obtain simple offline and online diagnosis of the combustion process through one-zone analysis, which provides the apparent heat release of the mixture. The present paper also starts from the in-cylinder pressure measurement to apply time frequency analysis for an alternative evaluation of the combustion events. A comparison with traditional one-zone analysis is then performed. In particular, time frequency analysis is here applied for the investigation of all the characteristic events that define the fuel ignition delay, i.e. hydraulic start of injection, first, along with the corresponding start of combustion, next. The study here reported is relative to single-injection patterns and has been applied to both conventional and premixed low temperature diesel combustion modes. For the considered injection pattern, time frequency analysis, compared to single-zone combustion model supplemented by measurements of injection rate at the hydraulic rig and by engine measurements of fuel injection pressure in the injector supply pipe, provided precise evaluation of the relevant combustion events.

Combustion characteristics of naphtha and n-heptane fuels in an auto-ignited HCCI engine at different lambda values and engine loads

In this study, it was aimed to control the HCCI combustion phase. For this purpose, low and high reactivity pure fuels and their mixtures in various ratios were tested. Reference n-heptane was chosen as the high reactivity fuel, while heavy naphtha was used as the low reactivity fuel. Detailed combustion analysis was performed using in-cylinder pressure data. IMEP, the start of combustion, combustion duration, indicated thermal efficiency, MPRR and COVimep maps were examined at different engine speeds and lambda values. Almost zero NOx and soot emissions were observed under all test conditions. On the other hand, CO and HC emissions were analyzed comparatively. It has been determined that HN75 fuel provides optimum operating conditions for HCCI combustion and also causes low CO and HC emissions. Indicated thermal efficiency was obtained at about 36% and in a wide operating range in the use of HN75 and HN100 fuels. This study shows that heavy naphtha fuel significantly improved combustion phase control in HCCI engines. Particularly remarkable results were obtained in terms of performance and emission values at 50% and 75% mixing ratios with n-heptane.