Relative Air-fuel Ratio Research Articles

Hydrogen-fueled PFI SI engine investigation for near-zero NOx emissions in de-throttled and supercharged ultra-lean burn conditions

Hydrogen-fueled PFI SI engine investigation for near-zero NOx emissions in de-throttled and supercharged ultra-lean burn conditions

Experimental Study on Spark Assisted and Hot Surface Assisted Compression Ignition (SACI, HSACI) in a Naturally Aspirated Single-Cylinder Gas Engine

Abstract Spark assisted compression ignition (SACI) represents an efficacious technique to extend the operating range and control combustion timing in homogeneous charge compression ignition (HCCI) engines. Recently, a hot surface ignition system (HSI) was demonstrated to enable hot surface assisted compression ignition (HSACI) featuring similar combustion characteristics compared to SACI. This work compares both combustion processes with regard to control and combustion characteristics, the strength of the ignition systems, and cycle-by-cycle variations (CCV). Engine trials were conducted using a single-cylinder research engine fueled with natural gas. The engine operated naturally aspirated at an engine speed of 1400 1/min and steady-state conditions. Experimental conditions cover relative air-fuel ratios λ = 2.1–3.1, intake temperatures Tin = 140–170 °C and intake pressures pin = 993–995 mbar. Results show similar capabilities of SACI and HSACI to control combustion timing by means of spark timing in SACI and hot surface temperature in HSACI. Heat release analyses of individual combustion cycles point out the similarity of both combustion processes. The evaluation of the strength of the ignition systems reveals that HSACI extends the lean limit by Δλ = 0.05–0.10 and advances the earliest applicable combustion timing (MinCA50) by ΔMinCA50 = 1.0–4.5 °CA provided that ringing is not of concern. Comparison of CCV in HCCI, SACI, and HSACI shows highest combustion stability for HCCI, followed by SACI. HSACI evinces highest CCV due to a larger variation at the start of combustion.

Investigations on energy efficiency enhancement under knock threshold limit conditions for a turbocharged direct-injection spark-ignition engine fueled with wet ethanol

Investigations on energy efficiency enhancement under knock threshold limit conditions for a turbocharged direct-injection spark-ignition engine fueled with wet ethanol

A Computational Study on the Influence of the Hydrous Ethanol Water Content in Spark-Ignition Engine Performance and in Flame Development

A multidimensional numerical model was developed to simulate the operation of one cylinder of a 1.4-liter flex-fuel spark-ignition engine. Hydrous ethanol with 4.3%, 7.5%, 10%, 15%, and 20% water volumetric contents were the considered fuels for the engine. The full load engine operating point was analyzed at 3,875 rpm with a relative air-fuel ratio of 0.9 and a fixed ignition delay. A Grid Convergence Index study was conducted to guarantee the accuracy of the obtained numerical solutions. A six consecutive mechanical cycle simulation was performed for hydrous ethanol with 4.3% water content, and experimental data were used for validation purposes. Turbulent flame speeds were also evaluated and analyzed. Numerical results showed that 10% water content led to the highest engine-generated power output and flame propagation speeds and to the lowest CO and unburned ethanol emissions among the tested fuels. The flame shape and encompassed volume were also analyzed. The results also showed that the high swirl in the in-cylinder flow affects the initial development of the flame for all water contents considered. Fuels leading to lower flame distortions early after ignition showed higher reaction rates and better performance.

Investigation of the benefits of passive TJI concept on cycle-to-cycle variability in a SI engine

During the last years, the sales of vehicles equipped with Spark-Ignition (SI) engines have increased, to the detriment of those powered by Compression-Ignition (CI) engines. However, SI engines provide lower efficiency than CI engines, due to the low compression ratio and stoichiometric mixture operation. A way to increase the efficiency of SI engines is lean combustion, as it allows to increase the specific heats ratio (γ) and reduces pumping losses at part loads. Nevertheless, the operation with extremely lean mixtures deals with ignition issues, promoting Cycle-to-Cycle Variability (CCV) and increasing the probability of misfire. The prechamber ignition concept, also known as Turbulent Jet Ignition (TJI), is a promising solution for enabling the implementation of lean combustion, without its drawback in SI engines. Such a concept can be implemented according to two approaches: In active TJI, there is an additional fuel supply system inside the prechamber, while in passive TJI there isn’t. Therefore, the main advantage of passive TJI is its simplicity, as the prechamber can be installed into a conventional spark plug body, with obvious benefits in terms of packaging and costs. In this work, the benefits of passive TJI on combustion and performance are assessed by simulation analyses. Particularly, a 1-D engine model was developed to simulate the TJI combustion and was validated versus experimental data. Afterward, a 0-D method was applied to assess the impact of the relative air-fuel ratio on CCV. The analysis was carried out in a high speed and load operating condition, namely 4500 rpm and 13 bar of IMEP, under both stoichiometric and lean mixture. Experimental and numerical results demonstrate the effectiveness of the passive TJI concept in promoting faster and more stable combustion also in lean-burn conditions.

Effects of intake charge temperature and relative air-fuel ratio on the deterministic characteristics of cyclic combustion dynamics of a HCCI engine

Homogenous charge compression ignition (HCCI) combustion can significantly reduce automotive pollution and increase the thermal efficiency of the engine. However, combustion phasing control is a major challenge in HCCI engines due to severe cyclic combustion variations. This study investigates the cyclic combustion dynamics of the HCCI engine using nonlinear dynamic methods such as return maps, recurrence plots (RPs), and recurrence quantitative analysis (RQA). Combustion stability and cyclic variations of HCCI combustion parameters were investigated on a modified four-stroke diesel engine. The experiments were conducted by varying relative air-fuel ratios ([Formula: see text]) and intake air temperatures ([Formula: see text]) at two engine speeds. In-cylinder pressure data of 2000 consecutive engine combustion cycles is logged for each test condition. In this study, deterministic characteristics of combustion phasing (CA50) and crank angle position of maximum cylinder pressure ([Formula: see text]) are investigated and compared by employing nonlinear dynamical methods. Return maps revealed that [Formula: see text] is having distinct and more frequently observed deterministic characteristics in comparison to CA50. Patterns in RPs showed a more persistent and sudden change in the combustion dynamics at higher engine speeds. Recurrence plot-based analysis found the existence of deterministic features in the combustion dynamics irrespective of the operating conditions. It was found using RQA parameters that the deterministic nature becomes stronger with a decrease in [Formula: see text] and any deviation in intermediate values of [Formula: see text]. Additionally, RQA measures advocate that CA50 has more deterministic characteristics at higher engine speed while [Formula: see text] at lower engine speed. Strong coupling and synchronization between [Formula: see text] and CA50 is indicated by cross-recurrence plots and CPR index when engine operated with a comparatively richer mixture.

Emissions and Performance of a Hybrid Hydrogen-gasohol E20 Fueled Si Engine

T his paper has investigated the effects of an alternative hybrid hydrogen-gasohol E20 fueled spark ignition engine on engine performance and exhaust pollutants. A hydrogen mixture with gasohol E20 was performed in an external mixture formation by installing a hydrogen fuel injection kit into the intake manifold area which is responsible for injecting hydrogen fuel into the inside of the engine’s cylinder. The hydrogen energy fraction in the intake was gradually increased from 3% to 9% ignition degree in the range of 20°, 25°, 30° and 35° before top dead center were controlled by using the electronic control unit to study the optimal condition for a four-stroke single-cylinder engine. In the steady-state test condition with half-open throttle under the variable load engine at 28%, 42%, 56%, and 70% of maximum engine torque, the engine can be available satisfactorily for an average relative air-fuel ratio (λ) value of 1.2 for hybrid hydrogen-gasohol E20 fuel. The results indicated that when the increase of hydrogen volume fraction. Postponing the spark timing was closer to top dead center (TDC) at 25° BTDC, the brake power and thermal engine efficiency increases. It is also noted that postponing the spark timing also caused NOx, HC and CO emissions to decrease. NOx emissions increased as the hydrogen volume fraction increased, whereas HC and CO emissions decreased.

Experimental study on controlled hot surface assisted compression ignition (HSACI) in a naturally aspirated single cylinder gas engine

Homogeneous charge compression ignition (HCCI) promises low [Formula: see text] emissions and high efficiency due to fast combustion at low temperatures. However, the control of combustion timing represents a serious challenge due to the lack of dedicated ignition control parameters. This challenge is addressed in this work by means of a hot surface ignition (HSI) system, whose core element consists of a shielded, electrically heated ceramic glow plug. In this approach, termed as hot surface assisted compression ignition (HSACI), a small portion of mixture is thought to ignite in the vicinity of the shielded glow plug and to subsequently propagate to the main combustion chamber in order to initiate bulk-gas auto-ignition. Adjusting the hot surface temperature enables to either advance or retard the onset of combustion and thus, allows to control combustion timing. This paper presents experimental results of initial engine trials, using the HSACI concept in a naturally aspirated single cylinder natural gas engine. Measurements were conducted at a constant engine speed of 1400 l/min and include intake air temperatures in the range of 150–175°C and relative air-fuel ratios ([Formula: see text]) from 2.0 to 2.8. Results show that the HSI system enables combustion under conditions, which do not allow for pure HCCI operation. Moreover, the combustion timing can be actively controlled within certain limits by changing the HSI temperature. Increasing cycle-to-cycle variations limit stable operation at lower temperatures, while a transition to pure HCCI is found at intake temperatures beyond 170°C. The applicable [Formula: see text] range is limited by knocking or uncontrolled combustion toward the rich side and instable operation toward the lean side. Loss analysis points out that wall heat flow and imperfect combustion represent the dominant loss mechanisms. Heat release analysis reveals two pronounced phases, indicating initial flame propagation and subsequent auto-ignition similar to spark assisted compression ignition (SACI).

Effect of hydrogen enrichment of compressed natural gas on combustible limit and flame kernel evolution in a constant volume combustion chamber using laser ignition

• Laser parameters optimized for laser beam pulse energy, and laser beam quality. • Lean-burn limits, flame kernel evolution, P-T Curve, and SoC determined for HCNG. • Flame kernel displacements were the maximum for λ = 1.1 for all HCNG mixtures. • Flame kernel displacements and combustible limits increased with H 2 enrichment. • Two-stage combustion increased with lowering λ and H 2 enrichment of CNG. • H 2 enrichment of CNG accelerated flame evolution from a 2D to a 3D phenomenon. Laser ignition of hydrogen-enriched compressed natural gas (HCNG) enables lean-burn combustion, a key technology for future emissions norms compliance for internal combustion (IC) engines. HCNG overcomes the limitations of low volumetric energy density and lowers the flame speed of CNG fueled spark ignition (SI) engine-powered vehicles. In this study, laser beam profile and beam quality (M 2 ) of a Q-switched Nd: YAG laser at fundamental wavelength of 1064 nm, having 6–9 ns pulse duration, were characterized. During the Constant volume combustion chamber (CVCC) experiments, relative air-fuel ratio (λ) of different HCNG blends were varied to identify the lean-burn limits, and observe flame kernel evolution, pressure–time history, and detect the start of combustion (SoC). At 10 bar initial chamber filling pressure, lean flammability limit increased due to hydrogen (H 2 ) enrichment of CNG. It was found to be λ = 1.6, 1.8, 1.9, 2.0, and 2.1 for CNG, 10HCNG (10% v/v hydrogen and balance CNG), 20HCNG, 30HCNG, and 40HCNG respectively. Flame kernel displacement (Early stages of flame initiation and its development in µs time-scale) was the highest for λ = 1.1 for all HCNG mixtures, irrespective of the test fuel composition. Knocking or two-stage combustion increased with lowering λ at 10 bar initial chamber filling pressure. SoC advanced and combustion duration (CD) decreased with increasing H 2 enrichment of CNG. Increased H 2 enrichment of CNG accelerated the flame kernel evolution and made it a predominantly a 3D combustion phenomenon (volumetric combustion). Lower λ and higher H 2 enriched CNG mixtures were effective in reducing the CD.

Clean combustion and emissions strategy using reactivity controlled compression ignition (RCCI) mode engine powered with CNG-Karanja biodiesel

• Karanja biodiesel-CNG used as alternate fuel in novel RCCI engine. • Combustion phasing and knock limit of RCCI engine. • Reduction in NO x and smoke emissions. • Improved BTE of RCCI engine. Heterogeneous combustion in a diesel engine is noisier, uncontrolled and more polluting. This can be achieved with a strategic approach of a reactivity-controlled compression ignition (RCCI) mode engine that operates with low and high reactive fuel combinations. In the present work, a diesel engine is operated in RCCI mode with gaseous fuels viz. CNG as a primary fuel and a blend of diesel and Karanja biodiesel (BD20) as pilot fuel. This research aims to determine the operating limits of CNG fuel for less noisy combustion and clean exhaust. Further, relative air-fuel ratio (λ), cycle to cycle variations, combustion noise and emissions were studied for full load operation. The CRDI engine is optimized for diesel operation with a split injection strategy. The knock limits for CNG as the primary fuel are obtained. The combustion noise increases at a higher energy share by CNG. Also, higher values of HC and CO emissions are observed. This may be due to higher energy share values, flame speed and octane number of CNG fuel. Further, NO x emissions and smoke are decreased. The CNG induction of 10 ms with 90% ES can be noted as a knock limit for 3.5 kW power. The highest BTHE of 24.2% and least BSFC 0.3 kg/kWhr reported by 60%ES of LRF is better than diesel and KBD20 fuel. An optimum 60% energy share of CNG is observed for clean combustion and emissions strategy using the RCCI mode of a modified diesel engine. Graphical Abstract

Development and comparative experimental investigations of laser plasma and spark plasma ignited hydrogen enriched compressed natural gas fueled engine

A customized port-fuel-injection (PFI) SI engine was operated in spark ignition (SI) and laser ignition (LI) modes at varying brake mean effective pressure (BMEP) and relative air-fuel ratio (λ) under naturally aspirated conditions. Test fuel used were hydrogen enriched compressed natural gas (HCNG) mixtures and results were compared with baseline CNG. For H2 enrichment of CNG, a customized dynamic fuel mixing system was developed. For LI, a solid state Q-switched Nd:YAG laser (200 mJ; 30 Hz; 6–9 ns) was used, and the laser beam was focused using a converging lens of 50 mm focal length. Experiments of HCNG fueling exhibited relatively higher peak pressure (Pmax) with its peak shifted closer to the top dead center (TDC). H2 enrichment of CNG led to increase in peak in-cylinder Pmax (by ∼2.9 bar), RoPR (by ∼0.72 bar/deg) and HRR (by ∼7.2 kJ/m3.deg) for 40HCNG compared to baseline CNG. The maximum BTE was observed to be ∼42.8% (at λ = 1.4) in LI mode for 30HCNG fueled engine. The lowest BSFC obtained were at λ = 1.2 for HCNG in SI mode, while corresponding value in LI mode was obtained at λ = 1.4. BSHC emissions were always lower for LI mode than the SI mode. At 3.96 bar BMEP, BSHC emissions reduced from 0.54 g/kWh (for CNG) to 0.35 g/kWh (for 40HCNG), which further reduced to 0.21 g/kWh (for H2) in LI mode. BSNOx emissions increased with increasing BMEP but reduced from 0.89 g/kWh at λ = 1.5 for CNG to 0.17 g/kWh for 30HCNG at λ = 1.7 at 30 Nm load.

On the improvement by laser ignition of the performances of a passenger car gasoline engine.

Laser ignition was used to operate a four-stroke, four-cylinder, multipoint fuel injection gasoline passenger car engine, replacing the engine classical ignition device. The laser ignition system was compactly built with diode end-pumped Nd:YAG/Cr4+:YAG composite ceramics, each laser spark plug delivering pulses at 1.06 μm with 4 mJ energy and 0.8ns duration at variable repetition rate, in accordance with the engine speed. The engine was operated at constant speed-constant load condition of 2000 rpm-2 bar equivalent brake mean effective pressure, and different ignition timings, thus simulating city traffic situations. Two relative air-fuel ratios have been considered: λ~1 for the stoichiometric mixture operation and λ~1.25 for the lean mixture condition. Parameters indicating engine performance, efficiency, combustion stability, and emissions have been measured and registered when groups of 500 consecutive cycles were acquired. The engine brake power, brake specific fuel consumption, coefficient of variability for indicated mean effective pressure, initial and main combustion stage durations, as well as exhaust emissions like carbon monoxide (CO) and total unburned hydrocarbons (THC) emphasized that significant improvements can be obtained for lean air-fuel mixture operation. Increases of the nitrogen oxides emission (NOx) were measured when laser ignition was used.

On the possibility to improve petrol engine operation by laser ignition

Abstract A typical method frequently used for the experimental investigation of engines operation at light load, low speed and different air-fuel ratios by spark timing adjustment was applied to understand in what measure the characteristics of the ignition system could improve the petrol engines performances. In this sense, a Laser Ignition - LI system replacing the original spark ignition system of the engine was mounted and some comparisons between these systems have been made based on engine power, coefficients of variation and combustion duration when 500 consecutive cycles were registered for 2000 rpm engine speed with load equivalent to 2 bar brake mean effective pressure and up to 1.25 relative air-fuel ratios.

Engine speed and air-fuel ratio effect on the combustion of methane augmented hydrogen rich syngas in DI SI engine

Abstract The main challenge on the fueling of pure hydrogen in the automotive vehicles is the limitation in the hydrogen separation from the product of steam reforming and gasification plants and the storage issues. On the other hand, hydrogen fueling in automotive engines has resulted in uncontrolled combustion. These are some of the factors which motivated for the fueling of raw syngas instead of further chemical or physical processes. However, fueling of syngas alone in the combustion chamber has resulted in decreased power output and increased in brake specific fuel consumption. Methane augmented hydrogen rich syngas was investigated experimentally to observe the behavior of the combustion with the variation of the fuel-air mixture and engine speed of a direct-injection spark-ignition (DI SI) engine. The molar ratio of the high hydrogen syngas is 50% H2 and 50% CO composition. The amount of methane used for augmentation was 20% (V/V). The compression ratio of 14:1 gas engine operating at full throttle position (the throttle is fully opened) with the start of the injection selected to simulate the partial DI (180° before top dead center (BTDC)). The relative air-fuel ratio (λ) was set at lean mixture condition and the engine speed ranging from 1500 to 2400 revolutions per minute (rpm) with an interval of 300 rpm. The result indicated that coefficient of variation of the indicate mean effective pressure (COV of IMEP) was observed to increase with an increase with λ in all speeds. The durations of the flame development and rapid burning stages of the combustion has increased with an increase in λ. Besides, all the combustion durations are shown to be more sensitive to λ at the lowest speed as compared to the two engine speeds.

EFFICIENCY AND CO2 EMISSION OF HEAT ENGINES OPERATING WITH HYDROGEN RICH GAS (HRG) ADDITION

The effects of gas addition on efficiency and CO2 emission were investigated with a compression ignition (CI) engine and a spark ignition (SI) engine operating with hydrocarbons-based fuels. Hydrogen rich gas (HRG) provided by an electrolyze, was aspirated into the air stream inducted in the engine cylinders. Investigation was conducted at engine light and medium loads and speeds, with relative low concentrations of HRG. For the CI engine, HRG addition up to 12.5% energetic fraction in fuel lowered CO2 concentration (ppm) in the engine exhaust up to 8% and BTE up to 1%. CO2 specific emission (g/kWh) was correspondingly lower with maximum 10%. For the SI engine fueled with gasoline, the effect of HRG addition was depending not only on engine load and speed, but also on the relative air-fuel ratio .. It was found for CO2 concentration a maximum decrease of 5% by HRG addition. BTE was improved in a limited domain of HRG fraction up to 20%, with maximum improvements between 2.5% and 21%. As a cumulative effect on CO2 concentration an on BTE a maximum lowering by 30% of the CO2 specific emission was reached. The effect of HRG supplementing LPG gas in the same SI engine was alternatively studied with similar results: CO2 concentration reductions by maximum 3%, some possible improvements of BTE up to 33% at HRG fraction of 19% and finally a lowering of CO2 specific emission by maximum 37%.

Real-time capable virtual NOx sensor for diesel engines based on a two-Zone thermodynamic model

This paper presents a control-oriented thermodynamic model capable of predicting nitrogen oxides (NOx) emissions in diesel engines. It is derived from zero-dimensional combustion model using in-cylinder pressure as the input. The methodology is based on a two-zone thermodynamic model which divides the combustion chamber into a burned and unburned gas zone. The original contribution of proposed method arises from: (1) application of a detailed two-zone modeling framework, developed in a way that the thermodynamic equations could be solved in a closed form without iterative procedure, which provides the basis for achieving high level of predictiveness, on the level of real-time capable models and (2) introduction of relative air-fuel ratio during combustion as a main and physically motivated calibration parameter of the NOx model. The model was calibrated and validated using data sets recorded in two different direct injection diesel engines, i.e. a light and a heavy-duty engine. The model is suitable for real-time applications since it takes less than a cycle to complete the entire closed cycle thermodynamic calculation including NOx prediction, which opens the possibility of integration in the engine control unit for closed-loop or feed-forward control.

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

Abstract 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.

The individual effects of cetane number, oxygen content or fuel properties on performance efficiency, exhaust smoke and emissions of a turbocharged CRDI diesel engine – Part 2

Abstract The paper presents the individual effects made by the variation of cetane number, fuel-oxygen content, or widely differing properties of diesel-HRD fuel blends involving ethanol (E) or biodiesel (B) on the performance efficiency, brake specific fuel consumption, exhaust smoke and NO x , CO, HC emissions of a turbocharged CRDI diesel engine. The dominant factors one after another operated separately to reveal their contribution to changes in operational parameters. Load characteristics were taken with a straight diesel and various (18 in total) fuel blends at maximum torque mode of 2000 rpm and additional speeds of 1500 and 2500 rpm to improve interpretation of the test results. The (bmep) characteristics were plotted as a function of relative air-fuel ratio (λ) to analyse performance and engine out emissions for relative ‘lambda’ values of = 1.30, 1.25 and 1.20, at the respective speeds of 1500, 2000 and 2500 rpm. Parameters obtained when using fuel blends of both E and B origins were compared with those measured with ‘base-line’ blends possessing normal CN rating or zero content of oxygen and a straight diesel to reveal the resulting development trends. The combustion characteristics (Part 1) were used to properly interpret the resulting changes in engine performance and emissions. The brake thermal efficiency equally increased by 0.5%, NO x emissions by 15.8% or 2.7%, smoke and CO decreased 1.7 times or by 34.9% and 7.2 times or increased by 18.8% when running with the most flammable (CN = 67.3) fuel blends E or B at λ = 1.20 and the high speed of 2500 rpm. The engine efficiency increased by 2.9% or 0.5%, NO x emissions by 10.6% (1.81 wt%) or 5.0%, smoke and CO emissions decreased 3.0 times or by 46.7% and by 63.3% (3.61 wt%) or 49.5% when using the most oxygenated (4.52 wt%) fuel blends series E or B under given test conditions.

The individual effects of cetane number, oxygen content or fuel properties on the ignition delay, combustion characteristics, and cyclic variation of a turbocharged CRDI diesel engine – Part 1

Abstract The study deals with the effects made by individual variation of cetane number, fuel-oxygen content, or widely differing properties of diesel-HRD fuel blends involving ethanol (E) or biodiesel (B) on the ignition delay, combustion phenomenon, maximum heat release rate, and the cyclic variation of a turbocharged CRDI diesel engine. The most important control factors one after another operated separately in this study to make a difference. Load characteristics were taken when running with a straight diesel and various (18) diesel-HRD fuel blends at maximum torque mode of 2000 rpm and speeds of 1500 and 2500 rpm to provide correct interpretation of the test results. Then, load (bmep) characteristics were plotted as a function of the relative air-fuel ratio (λ) and the analysis of combustion parameters was conducted for the ‘lambda’ values of λ = 1.30, 1.25 and 1.20, at the respective speeds of 1500, 2000 and 2500 rpm. Analysis of changes in the ignition delay, combustion characteristics, and the cyclic variation of parameters when using fuel blends of both origins was performed on comparative bases with the corresponding values measured with ‘base-line’ blends with CN = 51.2 or zero oxygen content and a straight diesel to reveal the potential developing trends. The enhanced cetane number of oxygenated fuels improved combustion and reduced cyclic variation when running at the high speed of 2500 rpm mainly. Whereas fuel-oxygen content should be neither too high nor too low, but just enough to assure complete combustion and low cyclic variation. The differing properties of the fuel involving ethanol or biodiesel were a separate factor strongly affecting diffusive combustion and the coefficient of cyclic variation (COV). Developing trends in the combustion characteristics were used to interpret the resulting changes in engine performance, emissions, and smoke (Part 2).

Comparative study of the simulation ability of various recent hydrogen combustion mechanisms in HCCI engines using stochastic reactor model

Abstract Hydrogen is a clean potential alternative fuel for internal combustion engines and completely eliminates the carbon based engine emissions (CO, CO 2 and unburned hydrocarbons). Homogenous charge compression ignition (HCCI) is a low temperature combustion mode with higher thermal efficiency and ultralow NO x emission. Hydrogen HCCI engine can combine potential benefit of fuel and combustion characteristics. In HCCI engine, combustion is governed by the chemical kinetics of the oxidation reactions. In-order to find a suitable reaction mechanism to numerically predict the combustion characteristics of hydrogen HCCI engine, 15 recent hydrogen combustion mechanisms are compared and analyzed. All mechanisms were simulated using a stochastic reactor model (SRM) to evaluate the combustion parameters for HCCI engine. Simulations were performed by varying inlet temperature (400–440 K), intake pressure (1.0–3.0 bar), engine speed (1000–3000 rpm) and relative air-fuel ratio (λ = 2 to 8) for all the mechanisms. Ignition delay predicted from different mechanism was compared with experimental data and ignition delay was also compared at engine like condition using all the test mechanisms. Error in prediction of different combustion parameters such as start of combustion (CA 10 ), maximum cylinder pressure (P max ) and maximum heat release rate (HRR max ) were evaluated using different hydrogen combustion mechanisms. It was found that a recently developed hydrogen mechanism (Maurya-2017) shows the closet resemblance with the experimental cylinder pressure data. The Oconaire-2004 mechanism was able to accurately predict the characteristics of hydrogen HCCI combustion. It was also found that NUIG-NGM-2010 and CRECK-2014 mechanisms were able to estimate the HCCI combustion characteristics under higher combustion temperature.