Piston Bowl Research Articles

Computational optimization of the piston bowl geometry for the different combustion regimes of the dual-mode dual-fuel (DMDF) concept through an improved genetic algorithm

Focusing on the dual-mode dual-fuel (DMDF) combustion concept, a combined optimization of the piston bowl geometry with the fuel injection strategy was conducted at various loads. An improved genetic algorithm was introduced in this study, which is superior in searching for the global optimal solutions. The optimal piston bowl shape coupled with the corresponding injection strategy was summarized at the various loads. The results show that the piston bowl geometry optimization can further improve the thermal efficiency with 1.4%, 4.4%, and 1.4% percentage points for the low, mid, and high loads, respectively. An indicated thermal efficiency up to 51.8% can be realized at mid load. Meanwhile, for all the optimal cases, NOx and soot emissions can meet the Euro VI limits.At low and mid loads, both the open and re-entrant type piston bowl can be equipped, while the high load only prefers the open type piston bowl for the DMDF mode. The re-entrant type or deep piston bowls are superior in organizing strong in-cylinder flow, which is beneficial for the fuel/air mixing. The open type or shallow piston bowls are helpful for reducing the heat transfer losses owing to the less heat transfer surface area. Furthermore, a correlation analysis was conducted to investigate the sensitivity of engine performance to the piston geometric parameters and injection parameters. It is concluded that the fuel injection event becomes more important for managing the engine performance as load increases. Among the injection parameters, the influence of the fuel injection timings and injection pressure on engine performance is more obvious. The piston geometric parameters play more significant roles in the heat transfer losses than the injection parameters for all loads. Among the geometric parameters, the most influential parameters are the width and open extent of the piston bowl. The heat transfer loss energy fraction can be well decreased with a wider and more open piston bowl.

Hydrogen and propane implications for reactivity controlled compression ignition combustion engine running on landfill gas and diesel fuel

A detailed investigation of employing landfill gas together with additives such as hydrogen or propane or both as a primary low reactivity fuel in a reactivity controlled compression ignition combustion of a diesel engine is conducted. A 3401E caterpillar single-cylinder diesel engine with a bathtub piston bowl profile is utilized to execute the study. The engine is operated at various intake pressures of 1.6, 1.9, and 2.2 bar, and runs at a fixed engine speed of 1300 rpm. For verification purposes, the conduct of the present engine running on pure methane as a low reactivity fuel is compared to that of the same engine available in the literature. Next, a numerical simulation is made to assess the performance of the present engine running on landfill gas plus the additives. Based on the obtained results, injecting either hydrogen or propane or a combination of both up to a total amount of 10% by volume to the premixed of landfill gas and air, and advancing diesel fuel injection timing of about 20–30 deg. crank angle, render the landfill gas utilization quite competitive with using methane alone. Applying an enriched landfill gas in a reactivity controlled compression ignition diesel engine, as a power generator, drastically reduces the greenhouse gas emission to the atmosphere. Also, the CO and UHC mole fraction in the exhaust gas can be eliminated by either advancing the start of diesel injection or using hydrogen or propane or both as additives. In addition, utilizing hydrogen or propane or a combination of both with the primary fuel improves the peak pressure to about 16% in comparison with that of landfill gas alone.

Effect of swirl ratio on charge convection, temperature stratification, and combustion in gasoline compression ignition engine

Various low-temperature combustion strategies (namely, homogeneous charge compression ignition, reactivity controlled compression ignition, and partially premixed charge compression ignition) have shown the potential to comply with upcoming and prevailing stringent emissions legislations. Low octane gasoline has emerged as an ideal fuel candidate for premixed charge combustion under diesel-like conditions in gasoline compression ignition (GCI) engines. GCI is an excellent technology to rectify future global energy demand imbalance, because it aims to replace diesel (which is in short supply) with low octane fractions/naphtha (which is in surplus supply) in compression ignition engines. However, this novel combustion concept requires modifications in the conventional design of diesel engines. The combustion chamber shape and in-cylinder flows play a crucial role in charge distribution and temperature stratification. Therefore, understanding the combined effect of combustion chamber geometry and in-cylinder flows is essential for future engine designs. GCI combustion engine simulations for varying swirl ratios (SRs) were performed in CONVERGE CFD software to understand the effect of in-cylinder air motion on the mixture stratification and combustion. A 1/7th sector geometry for a conventional re-entry piston bowl was modeled and then simulated. Two different mechanisms were used for model validation. The results indicated that the large-scale flow structures govern the fuel distribution in the combustion chamber. The charge convection because of increased swirl has a substantial effect on the combustion characteristics of the engine. A distinguished ignition kernel was observed for all test cases. An interfacial region with counter-rotating vortices formed a lean mixture zone, hindering flame propagation and combustion. A lower SR, shallow depth piston, and modifications to avoid flame quenching in the squish zone need to be further investigated to optimize the engine performance.

Optimization of the combustion chamber geometry and injection parameters on a light-duty diesel engine for emission minimization using multi-objective genetic algorithm

Combustion efficiency and exhaust emission of the compression-ignition engines are highly dependent on the combustion chamber design. In this study, shape optimization was performed to reduce the emissions and maximize the combustion efficiency of a compression ignition engine with the guidance of computational fluid dynamics (CFD). The aim was to optimize diesel combustion efficiency while maintaining engine power and torque. A double-swirl piston bowl is used, and the bowl depth, bowl diameter, and other dimensions of the piston bowl are optimized to minimize the soot and NOX emission while meeting the IMEP target. The spray angle of the injector, SOI, and injector protrusion were parametrized to meet the optimization targets. The numerical model was developed using Converge software. CAESES software and multi-objective genetic algorithm (MOGA) were used to automatically change the chamber design parameters and to optimize the piston bowl geometry. A total of 104 different combustion chamber designs and 23 varied injection parameters were determined parametrically and the optimum case was decided with the MOGA. A comprehensive optimization study was carried out using experimental, CFD, and MOGA methods. Compared to the baseline design, the optimized new piston bowl design has provided enhanced in-cylinder air utilization and rapid mixing-controlled combustion, resulting in enhanced fuel efficiency. The optimized design emits remarkably lower NOX and soot emissions.

Numerical investigation of injection parameters and piston bowl geometries on emission and thermal performance of DI diesel engine

Tightening noose on engine emission norms compelled manufacturers globally to design engines with low emission specially NOx and soot without compromising their performance. Amongst various parameters, shape of piston bowls, injection pressure and nozzle diameter are known to have significant influence over the thermal performance and emission emanating from the engine. This paper investigates the combined effect of fuel injection parameters such as pressure at which fuel is injected and the injection nozzle size along with shape of piston bowl on engine emission and performance. Numerical simulation is carried out using one cylinder naturally aspirated diesel engine using AVL FIRE commercial code. Three geometries of piston bowls with different tumble and swirl characteristics are considered while maintaining the volume of piston bowl, compression ratio, engine speed and fuel injected mass constant along with equal number of variations for injection nozzle size and pressures for this analysis. The investigation corroborates that high swirl and large turbulence kinetic energy (TKE) are crucial for better combustion. TKE and equivalence ratio also increased as the injection pressure increases during the injection period, hence, enhances combustion and reduces soot formation. Increase in nozzle diameter produces higher TKE and equivalence ratio, while CO and soot emission are found to be decreasing and NOx formation to be increasing. Further, optimization is carried out for twenty-seven cases created by combining fuel injection parameters and piston bowl geometries. The case D2H1P1 (H1 = 0.2 mm, P1 = 200 bar) found to be an optimum case because of its lowest emission level with slightly better performance.

Development of an Efficient Conjugate Heat Transfer Modeling Framework to Optimize Mixing-Limited Combustion of Ethanol in a Diesel Engine

Abstract Mixing controlled combustion of alcohol fuels has been identified as a promising technology based on their low propensity for particulate and NOx production, but the higher heats of vaporization and auto-ignition temperatures of these fuels make their direct use in diesel engine architectures a challenge. To realize the potential of alcohol-fueled combustion, a computational fluid dynamics (CFD) modeling framework is developed, validated, and exercised to identify designs that maximize engine thermal efficiency. To evaluate the use of thermal barrier coatings (TBCs), a simplified one-dimensional (1D) conjugate heat transfer (CHT) modeling framework is employed. The addition of the 1D CHT model only increases the computational expense by 15% relative to traditional approaches, yet offers more accurate heat transfer predictions over constant temperature boundary conditions. The validated model is then used to explore a range of injector orientations and piston bowl geometries. Using a design of experiments (DoE) approach, several designs were identified that improved fuel–air mixing, shortened the combustion duration, and increased thermal efficiency. The most promising design was fabricated and tested in a Caterpillar 1Y3700 single-cylinder oil test engine (SCOTE). Engine testing confirmed the findings from the CFD simulations and found that the co-optimized injector and piston bowl design yielded over 2-percentage point increase in thermal efficiency at the same equivalence ratio (0.96) and over 6-percentage point increase at the same engine load (10.1 bar indicated mean effective pressure (IMEP)), while satisfying design constraints for peak pressure and maximum pressure rise rate.

Potential of reactivity-controlled compression ignition with reverse reactivity stratification (R-RCCI) fueled with gasoline and polyoxymethylene dimethyl ethers (PODEn)

To improve the trade-off between thermal efficiency and peak heat release rate (HRR) of partially premixed combustion (PPC) and the combustion efficiency of reactivity-controlled compression ignition (RCCI), the combustion mode with premixed high-reactivity fuel and direct-injection (DI) low-reactivity fuel, called RCCI with reverse reactivity stratification (R-RCCI), was explored at low loads in a light-duty diesel engine in this study. Compared with diesel, polyoxymethylene dimethyl ethers (PODEn) has better volatility, which is beneficial for the formation of premixed charge, so it was used as the premixed high-reactivity fuel for R-RCCI in this work. The gasoline and P20G80 (PODEn/gasoline blends with the volume fraction of 20%/80%) were respectively applied as the DI low-reactivity fuel. By investigating the combustion characteristics of R-RCCI, it is found that R-RCCI can break the trade-off between combustion efficiency and nitrogen oxides (NOx) emissions. This is because the combustion efficiency of R-RCCI is dominated by the spray location of the DI fuel rather than the 50% burn point (CA50). As the start of injection (SOI) timing is retarded, the fuel injected within the piston bowl increases, and combustion efficiency, as well as indicated thermal efficiency (ITE), is considerably promoted. Meanwhile, CA50 progressively retards with delayed SOI timing, which effectively reduces NOx emissions. The soot emissions of R-RCCI are also extremely low. The maximum ITE of PODEn/P20G80 R-RCCI is significantly higher than that of PODEn/gasoline R-RCCI. This occurs because the higher reactivity of P20G80 can reduce the sensitivity of CA50 to SOI timing and improve combustion stability, so a more delayed SOI timing is allowed to improve ITE. With the same engine configurations, R-RCCI can reduce peak pressure rise rate and improve combustion stability, while enhancing combustion efficiency and ITE compared with RCCI at the low-load conditions tested in this study.

A Comparative Numerical Study of the Combustion Performance of the Syngas-Fueled HCCI Engine Using a Toroidal Piston, Square Bowl Piston, and Flat Piston Shape at Different Loads

Abstract This study analyzes the combustion performance of a syngas-fueled homogenous charge compression ignition (HCCI) engine using a toroidal piston (baseline piston), square bowl, and flat piston shape, at low, medium, and high loads, with a constant compression ratio of 17.1. In this study, the square bowl shape is optimized by reducing the piston bowl depth and squish area ratio (squish area/cylinder cross-sectional area) from 34 to 20, 10, and 2.5% and compared with the flat piston shape and toroidal piston shape. This HCCI engine operates under an overly lean air–fuel mixture condition for power plant usage. ansys forte cfd package with GRI Mech3.0 chemical kinetics is used for combustion analysis, and the calculated results are validated by the experimental results. All simulations are accomplished at maximum brake torque (MBT) by altering the air–fuel mixture temperature at intake valve closing (IVC) (TIVC) with a constant equivalence ratio of 0.27. This study reveals that the main factors that affect the start of combustion (SOC), maximum pressure rise rate (MPRR), combustion efficiency, and thermal efficiency by changing the piston shape are the squish flow and reverse squish flow effects. Therefore, the square bowl piston D is the optimized piston shape that offers low MPRR and high combustion performance for the syngas-fueled HCCI engine, due to the weak squish flow and low heat loss rate through the combustion chamber wall, respectively, when compared with the other piston shapes of square bowl piston A, B, and C, flat piston, and toroidal (baseline) piston shape.

A Computational Investigation of PPCI-Diffusion Combustion Strategy at Full Load in a Light-Duty GCI Engine

<div class="section abstract"><div class="htmlview paragraph">A two-stage PPCI-diffusion combustion process recently showed good potential to enable clean and fuel-efficient gasoline compression ignition (GCI) combustion at medium-to-high loads. By conducting closed-cycle 3-D CFD combustion analysis, a further step was undertaken in this work to evaluate and optimize the PPCI-diffusion combustion strategy at a full load operating point (2000rpm-23.5 bar IMEPcc) while keeping engine-out NOx below 1 g/kWh.</div><div class="htmlview paragraph">The light-duty GCI engine used in this investigation featured a custom-designed piston bowl geometry at a 17.0 compression ratio (CR), a high pressure diesel fuel injection system, and advanced single-stage turbocharging. A split fuel injection strategy was used to enable the two-stage PPCI-diffusion combustion process.</div><div class="htmlview paragraph">First, the injector spray pattern and swirl ratio effects were evaluated. In-cylinder air utilization and the PPCI-diffusion combustion process were notably influenced by the closed-cycle combustion system design. Among the different spray patterns at a swirl ratio of 0, the one with 120° spray inclusion angle, 8-hole, and 1.5 times total nozzle area (TNA) was favored due to enhanced late-stage fuel-air mixing and more rapid diffusion combustion. In the second step, a fuel injection strategy optimization campaign was performed through a space-filling Design of Experiments (DoE) approach. Overall, the optimized injector spray pattern and the optimized fuel injection strategy together were predicted to produce 5.1% lower ISFC and 50% soot reduction over the baseline. A competitive analysis showed the optimized PPCI-diffusion combustion strategy had the potential to generate substantially lower NOx and soot than a modern light-duty diesel engine at full load.</div></div>

Improving of CI engine performance using three different types of biodiesel

Currently, most automotive industries use fossil fuels, like diesel fuel, which are harmful for the environment and are known as the main reason for global warming. To reduce the adverse effects of these fuels, scholars have investigated and suggested green fuels like biodiesel. However, further studies should be conducted to improve the functionality of biodiesel fuel in diesel engines. In the current study, three completely distinct biodiesel fuels (namely, B1 with 96 % lauric oil, B2 with 88 % oleic oil, and B3 with 89.5 % ricinoleic oil) were numerically evaluated to carefully investigate the effects of the number of carbon atoms, the OH bond, and viscosity on the performance of a CI engine. First, the predicted in-cylinder pressure, the rate of heat released, and NO emissions were compared to experimental results and an appropriate accord was obtained. For the mentioned biodiesels, the parameters of engine speed, injection angle, piston bowl center depth, and compression ratio were investigated by CFD code under different engine speeds. It was found that changing the piston bowl center depth (PBCD) value from 0.0042 to 0.009 m increased NO and the indicated power by 4% and 3%, respectively, for B1, B2, and B3 biofuels. In addition, when the engine was fueled by Corylus avellana biodiesel, the change in compression ratio from 16 to 24 increased peak pressure and torque by around 77 % and 17 %, respectively. The results showed that the cylinder fueled by high viscosity biodiesel has lower air-fuel mixing. A fuel that has more oxygen atoms in its chemical structure can produce higher NO emissions. Moreover, the injection angle of 150° led to increased fuel consumption rate and indicated power compared to the injection angle of 160°. It was determined that the compression ratio has significant effects on emission and combustion characteristics.

Piston Bowl Geometry Effects on Gasoline Compression Ignition in a Heavy-Duty Diesel Engine

Abstract A design optimization campaign was conducted to search for improved combustion profiles that enhance gasoline compression ignition in a heavy-duty diesel engine with a geometric compression ratio of 17.3. A large-scale design of experiments approach was used for the optimization, employing three-dimensional computational fluid dynamics simulations. The main parameters explored include geometric features, injector specifications, and swirl motion. Both stepped-lip and re-entrant bowls were included in order to assess their respective performance implications. A total of 256 design candidates were prepared using the software package CAESES for automated and simultaneous geometry generation and combustion recipe perturbation. The design optimization was conducted for three engine loads representing light to medium load conditions. The design candidates were evaluated for fuel efficiency, emissions, fuel–air mixing, and global combustion behavior. Simulation results showed that the optimum designs were all stepped-lip bowls, due to improvements in fuel–air mixing, as well as reduced heat loss and emissions formation. Improvements in indicated specific fuel consumption of up to 3.2% were achieved while meeting engine-out NOx emission targets of 1–1.5 g/kW · h. Re-entrant bowls performed worse compared to the baseline design, and significant performance variations occurred across the load points. Specifically, the re-entrant bowls were on par with the stepped-lip bowls under light load conditions, but significant deteriorations occurred under higher load conditions. As a final task, selected optimized designs were then evaluated under full-load conditions.

Investigation on Combining Partially Premixed Compression Ignition and Diffusion Combustion for Gasoline Compression Ignition—Part 2: Compression Ratio and Piston Bowl Geometry Effects

Investigation on Combining Partially Premixed Compression Ignition and Diffusion Combustion for Gasoline Compression Ignition—Part 2: Compression Ratio and Piston Bowl Geometry Effects

Experimental investigation of porous media combustion applied on the piston bowl of diesel engine

The attainment of homogenous combustion in diesel engines has always been a challenge. The erstwhile literatures reported the potential of porous media (PM) in enhancing the homogeneity of fuel–air mixture in various combustion devices. Taking cognisance of this fact, it was attempted to apply PM on the piston bowl of the diesel engine to study the consequent efficacy of homogenous combustion. It was revealed from the study that with the application of PM on the piston bowl, the evaporation rate of the fuel mixture was enhanced (shorter ignition delay) and mechanical efficiency was also improved as compared to the conventional engine. Compression tests were performed for the three commercially available PMs, like silicon carbide, alumina and zirconia, to determine their load bearing capacity inside the engine during operation. Silicon carbide was found to have better material strength to resist load. Also, experimental analysis was conducted by the use of cylindrical shaped silicon carbide fixed in the cylindrical piston bowl, which was modified from the traditional hemispherical one. The standard volumetric compression ratio of 17.5 and the porosity of ~ 78% were considered for PM. The experiments were performed at different part loads with PM for the safe operation of the engine. The mechanical efficiency ( $$\eta_{{\text{m}}}$$ ) was found to enhance by ~ 9% and ignition delay got advanced by ~ 2° crank angle with PM. Emission parameters with PM, such as nitrogen oxides (NOX) and carbon dioxide (CO2) were reduced up to ~ 62% and ~ 39%, respectively, than those of conventional diesel engine.

Combined effect of Phoenix dactylifera biodiesel and multiwalled carbon nanotube–titanium dioxide nanoparticles for modified diesel engines

This investigation addressed Phoenix dactylifera biodiesel (PDME) production using an ultrasound-assisted transesterification process. The produced Phoenix dactylifera biodiesel (PDME25) was blended with different concentrations of multiwalled carbon nanotubes and titanium dioxide (TiO2). Diethyl ether (DEE, 1% vol.) and sorbitan oleate (Span80, 2% vol.) surfactants were used to enhance and stabilize nanoparticles for the physiochemical properties in the base fluids. The piston bowl geometry was modified to a toroidal type for better swirl and squish motion, and a six-hole fuel injector was used for enhanced atomization. The BTE and HRR improved by 22.9% and 20.1%, respectively, while the CO, HC, smoke emissions, BSFC, and ignition delay decreased by 32.8%, 23.8%, 13.4%, 25.2%, and 19.08%, respectively. The results showed that the blend of potential biodiesel sources, viz. Phoenix dactylifera and MWCNT–TiO2 nanoadditives, delivered comparable diesel fuel properties.

Experimental evaluation of orange oil biodiesel in compression ignition engine with various bowl geometries

ABSTRACT In the recent decades, energy production and consumptions elevated owing to heavy demand and rapid progress in the automobile sector. In this research work, orange oil biodiesel was produced from transesterification of non-edible oil orange oil. The biodiesel is blended in various proportions with diesel under volumetric conditions and termed as B1 (25% orange oil biodiesel with 75% conventional fuel), B2 (50% orange oil biodiesel with 50% conventional fuel), B3 (75% orange oil biodiesel with 25% conventional fuel) and B4 (100% orange oil methyl ester) samples, respectively. Two distinct bowl shapes were developed specifically hemispherical combustion shape (CGB1) and toroidal combustion shape (CBG2) in diesel engine to evaluate engine characteristics. On comparing with CBG1, increased efficiency and decreased fuel consumption were observed with CBG2. Lower engine exhaust emissions like smoke, carbon monoxide and hydrocarbon were identified in CBG2 than CBG1 excluding oxides of nitrogen. The custom of using low viscous orange oil methyl ester with piston bowl geometry modification was considered to be the beneficial approach for attaining upgraded engine characteristics.

Open source extensions applied to meshing problems for KIVA 4

ABSTRACT KIVA is a very successful software that was released around 1985. One of its advantages is the capacity to include computer routines made by the users. That is why it is mostly used for research and development and as a tool for simulation driven design and optimization of internal combustion engines. As with many CFD software, mesh generation with KIVA is time consuming when its own meshing program is used. This can be exacerbated in the case of complex geometries with a special mesh quality, or when unstructured meshes are needed. Commercially, there are several meshing tools that have features and are available for a price. But this study explores mesh generation for KIVA in four cases of difficult geometries using open source tools. This allows to control all the meshing steps and parameters like mesh refinement, anisotropy and directionality. The first case is a Venturi tube with diesel spray injected in the middle of the throat. The second one an unstructured mesh for an eccentric diesel piston bowl. The last two cases are hybrid meshing methods for an engine with two valves and a pre-chamber, and an engine with two valves and a non-axisymmetric bowl. All the cases were validated in KIVA. This study extends the applicability of KIVA in terms of possibilities and ease of mesh generation. Users can use their preferred CAD/mesh software and convert it to KIVA if the format is compatible with OpenFOAM. Accordingly, the presented methodology would reduce the time devoted to meshing.

Characterization of combustion process and emissions in a natural gas/diesel dual-fuel compression-ignition engine

Dual-fuel (DF) combustion using natural gas and diesel has received considerable attention in the on- and off-road freight transportation sectors owing to its potential use in achieving better fuel economy and cleaner combustion. To determine the effect of the natural gas/diesel mixture quality on the combustion process and pollutant emission, high-speed flame visualization was used to investigate the phenomena of natural gas (NG)/diesel DF combustion in a 1.0 L optically-accessible single-cylinder engine. The diesel injection timing and natural gas substitution ratio (NGSR) were varied to implement diverse in-cylinder blending conditions under constant fuel energy input. A novel flame regime separation method based on color image segmentation in a hue-saturation-value (HSV) color space was used to quantitatively compare the spatial distributions of premixed and diffusion flame regimes. Because NG has a lower carbon content and higher auto-ignition resistance compared with diesel, the natural luminosity images for larger NGSRs revealed a significant reduction in the diffusion flame regime accompanied by retarded flame development. An earlier injection of the liquid diesel shifted the location of the early flame growth toward the piston bowl wall and created a rapid influx of propagating flame, while effectively suppressing the formation of intense soot radiation through longer ignition delay. These observations were verified by the exhaust emissions measured using the full-metal version of the engine and the same fuel supply parameters, specifically regarding the behavior of the smoke and nitrogen oxide emissions.

Experimental investigations of a single cylinder four stroke diesel engine using modified piston bowl fuelled with Jojoba biodiesel blend

This investigation deals with the influence of squish on the piston bowl in single cylinder 4 S compressed ignition engine fuelled with jojoba biodiesel and its effect on performance, emission and combustion characteristics. The squish area and its corresponding velocity are varied by changing the piston bowl cross-section without altering the piston bowl volume so as to obtain improved performance, emission and combustion characteristics. The velocity and squish effects are analyzed using CFD (Computational Fluid Dynamics) for the standard piston. The results obtained are compared with the modified piston having an octagonal bowl shape in the piston combustion chamber. The performance and combustion characteristics like brake specific fuel consumption, brake thermal efficiency and pressure vs. crank angle and heat release rate are studied. Also, emission parameters such as (carbon monoxide), HC (hydrocarbons) and NOx (oxides of nitrogen) were measured from the tail end of the exhaust pipe. The objective of this work to optimize the combustion chamber geometries using octagonal bowl combustion chamber and the results are compared with the standard hemispherical combustion chamber. A significant increase in brake thermal efficiency is noticed for octagonal piston bowl. There is a reduction in HC, CO which are seen while using octagonal bowl piston compared with the standard piston.

Influence of reentrant piston bowl geometry on combustion in CI engine

The geometry of the piston bowl can affect flow, turbulence, mixing and combustion in an engine. In addition, the optimum geometry can be fuel specific. In this work, the effect of the piston bowl geometry variation on combustion of Dimethyl Ether (DME) in a compression ignition engine is investigated computationally by using AVL FIRE software. A reentrant piston bowl configuration is taken and the bowl diameter is varied while keeping the clearance at TDC, compression ratio (17.8) and operating conditions same. The objective is to exploit the non-sooting characteristics of DME and get an understanding of the re-entrant geometry for NO minimization without compromising the efficiency. Results show that there is negligible effect of the geometry on pressure traces and efficiency. However, geometry does have an influence on flow near TDC and thereby affects fuel/air mixing. It is noted that the geometry with the largest bowl diameter led to relatively rapid combustion and higher NO emissions. In contrast, the geometry with the smallest bowl diameter showed more prominent tail in the heat release rate and lowest NO emissions. Based on this work, the re-entrant configuration with smaller bowl diameter is preferred.

Numerical Investigation of Reactivity Controlled Compression Ignition Engine Performance under Fuel Aggregation Collision to Piston Bowl Rim Edge Situation

To better homogenize the mixture of fuel and air in the combustion chamber and to enhance the controllability of ignition timing in Reactivity Controlled Compression Ignition (RCCI) engines, controlling the start of injection (SOI) timing can be essential. By changing the SOI timing, at some specific crank angles (CAs), the fuel can impact the edge of the piston bowl and create some difficulties. In this research, initially, efforts are made to recognize the range of SOI timing in which this collision process takes place (in the range of 44-54° bTDC), then, performance and the emission levels of the engine were evaluated in the beginning and end of this interval. The findings suggest that the nitrogen oxides emissions and the maximum in-cylinder mean pressure are higher in SOI of 44° bTDC, as compared to those in the SOI timing of 54°bTDC, although the latter has higher ignition delay and unburnt hydrocarbon (UHC) emission. Moreover, some evaluations were carried out to examine how the temperature of the fuel-air mixture can affect the performance of the engine in this specific range. It was found that as the IVC temperature increases, it rises the indicated mean effective pressure (IMEP), in-cylinder pressure, and NOx emission.