In-cylinder Combustion Temperature Research Articles

Emission Spectroscopy-Based Sensor System to Correlate the In-Cylinder Combustion Temperature of a Diesel Engine to NOx Emissions.

Due to a rising importance of the reduction of pollutant, produced by conventional energy technologies, the knowledge of pollutant forming processes during a combustion is of great interest. In this study the in-cylinder temperature, of a near series diesel engine, is examined with a minimal invasive emission spectroscopy sensor. The soot, nearly a black body radiator, emits light, which is spectrally detected and evaluated with a modified function of Planck's law. The results show a good correlation between the determined temperatures and the NOx concentration, measured in the exhaust gas of the engine, during a variety of engine operating points. A standard deviation between 25 K and 49 K was obtained for the in-cylinder temperature measurements.

A Visual Study on of HCB/Gasoline Dual-Fuel Combustion Strategy and Premix Ratio in a Diesel Engine

Article A Visual Study on of HCB/Gasoline Dual-Fuel Combustion Strategy and Premix Ratio in a Diesel Engine Qian Wang *, Botian Guo, Lixuan Cao, Xu Liu, Yi Jiang, and Jiawei Yao School of Energy and Power Engineering, Jiangsu University, Zhenjiang 212013, China * Correspondence: qwang@ujs.edu.cn Received: 8 November 2023 Accepted: 22 January 2024 Published: 30 January 2024 Abstract: This study investigates the combustion characteristics of hydrogen catalysed biodiesel (HCB) ignited gasoline in an optical engine using the Reactivity Controlled Compression Ignition (RCCI) combustion model. The experiment uses a single injection strategy to determine the optimum injection timing for gasoline ignition by varying the HCB injection timing (-30 to -15° CAATDC) and the ratio of high to low reactivity fuel energy (10% to 30%), to investigate the gasoline premix ratio, and to analyse the flame development characteristics. The results indicate that as the HCB energy ratio increases, the in-cylinder pressure and heat release rate increase significantly, and the in-cylinder combustion temperature improves significantly. As the injection timing is delayed, the combustion phase shifts back, and when the injection timing is close to the upper stop, the in-cylinder combustion pressure and heat release rate increase first increase and then decrease. Based on the results, it can be concluded that optimising the HCB injection timing and energy ratio can effectively control the distribution of the fuel-air mixture in the combustion chamber, thereby improving combustion efficiency and emission performance. By strategically adjusting the injection timing, an ideal balance between fuel stratification and flame propagation can be achieved, which ultimately improves the overall combustion process. The results of this study provide valuable insights for the further development of combustion control strategies and contribute to the development of more efficient and environmentally friendly engine technologies.

Investigation on formaldehyde generation characteristics and influencing factors of PODE/methanol dual-fuel combustion mode.

Polyoxymethylene dimethyl ether (PODE) and methanol are important low-carbon substitutable fuels for reducing carbon emissions in internal combustion engines. In the research, the impacts of methanol ratio, injection timing, and intake temperature on HCHO generation and emission were investigated using both engine tests and numerical simulations. Results suggest that an increase in methanol ratio suppresses auto-ignition tendency of PODE, leading to the increase of ignition delay period, pressure peak, and heat release rate peak inside the cylinder. The decrease in in-cylinder combustion temperature contributes to an increase in HCHO emission due to partial oxidation of methanol in the cylinder and exhaust pipe. While the injection timing is gradually postponed from -10 °CA ATDC to 2 °CA ATDC, in-cylinder high-temperature area decreases, the quantity of unburned methanol increases, but part of HCHO is converted to HCO due to H radical influence, resulting in 72% increased HCHO emission. With the increment of intake temperature, the oxidation and decomposition of in-cylinder methanol accelerate, leading to an improvement in combustion stability, more uniform temperature distribution, and a decrease in unburned methanol, which results in lower HCHO emission. When the intake temperature is rose from 30 to 60 °C, HCHO emission decreases by 11.2%.

Experimental investigation of the influence of pre-chamber structural parameters on combustion and emission characteristics of a high compression ratio SI engine

The passive pre-chamber exhibits great potential for practical applications in the internal combustion engine due to its simple structure. However, it faces difficulties in scavenging process, making optimization of pre-chamber structure particularly important. In this study, the effects of pre-chamber ignition systems with different structures and original spark ignition were conducted on a high compression ratio direct-injection SI engine to investigate the combustion, performance, and emission characteristics. The results show that the increase in pre-chamber volume weakens the in-cylinder combustion process and engine performance, while increasing the pre-chamber orifice diameter can enhance the combustion stability at medium to high loads, but will weaken the engine performance at low load. Compared to spark ignition, pre-chamber ignition results in an earlier 50% combustion position, a shorter combustion duration and lower COVIMEP, with these effects becoming stronger as load increases. At high load, the pre-chamber ignition (PC1) advances the 50% combustion position by 5.6°CA and shortens the combustion duration by 16.7%. In addition, the indicated thermal efficiency of the pre-chamber ignition achieves an increase of 0.84% at the optimal point and 2.5% at high load. Overall, using the smaller orifice diameter and volume in the pre-chamber can improve in-cylinder combustion process and increase thermal efficiency across the load range. For emission analysis, the pre-chamber ignition leads to an increase in NOx and HC emissions due to the influence of in-cylinder combustion temperature and quenching effect, while the CO emissions are similar to spark ignition.

A comparative study for the n-butanol/n-octanol and n-butanol/ di-n-butylether fueled dual-fuel engines with different injection timings

In this study, numerical simulations were performed to compare the combustion and emission characteristics of n-butanol/n-octanol (B/O) and n-butanol/di-n-butylether (B/D) dual-fuel engines at the different start of injection (SOI) timings. The three-dimensional dual-fuel engine simulation was implemented by coupling KIVA-CHEMKIN with a multi-component chemical reaction mechanism containing n-butanol, n-octanol, and di-n-butylether (DnBE). The reliability of the numerical models was verified by comparing the simulated and experimental in-cylinder pressure, heat release rate (HRR), and emissions. Then B/O and B/D dual-fuel engines with different premixed n-butanol ratios (B0, B10, B20, B30, and B40) were simulated at 1500 rpm with normal SOI timing (7 deg BTDC) and advanced SOI timing (20 deg BTDC), respectively. It has been found that an increased ratio of premixed fuel would increase the peak cylinder pressure due to the higher oxygen content of n-butanol. The change of SOI timing has a significant effect on the B/O engine and a minor influence on the B/D engine. When the SOI timing is advanced from 7 deg BTDC to 20 deg BTDC, the B/O engine changes from premixed to premixed-diffusion combustion phase. In addition, the B/O engine exhibits a more significant reactivity-controlled combustion mode under advanced SOI timing. In terms of emissions, the B/O engine emits more CO than the B/D engine, which is due to the fact that n-octanol is less volatile, resulting in more local high equivalence ratio areas in the cylinder. Since the in-cylinder combustion temperature and combustion duration of the B/O engine are less than those of the B/D engine, the NOx emissions of the B/O engine are lower. With advanced SOI timing, the addition of premixed n-butanol can reduce both CO and NOx, but the emission values are still high and further optimization is needed.

Combustion and emission performance of isopropanol-butanol-ethanol (IBE) mixed with diesel fuel on marine diesel engine with nano YSZ thermal barrier coating

The effect of piston coating on the combustion and emission performance of IBE and diesel blended fuel was experimental studied. The experimental conditions were set to be a orthogonal matrix of three loads from low to high, coated and uncoated, IBE20 fuel and D100 fuel. The heat release rate, ignition delay periods and combustion duration were calculated by the cylinder pressure curves. The break thermal efficiency was calculated by the fuel consumption rate, and the concentration of soot, NOx and CO in the exhaust was collected. It was found that Nano-YSZ thermal barrier coating (TBC) can effectively reduce heat transfer loss, increase in-cylinder combustion temperature, and effectively solve the problems of high latent heat of vaporization and ignition delay of alcohol fuel. The experimental results showed that the Nano-YSZ coating could effectively reduce the brake specific fuel consumption, which was reduced by 5% when using pure diesel under 25% load, and was reduced by 7.3% for IBE20 fuel. Furthermore, TBC_IBE20 (IBE20 used in TBC Engine) exhibited the highest thermal efficiency under the three working conditions. Under all operating conditions, IBE20 had the potential to reduce soot emissions but increase NOx emissions, and thermal barrier coatings could amplify this potential.

Numerical analysis of the performance and NOx emission of a diesel engine fueled with algae biofuel-diesel blends

ABSTRACT Researchers are looking for alternative energy sources, and biofuel from algae has a significant contribution as an alternative renewable fuel. This paper aims to evaluate fundamental running parameters (heat release rate, peak pressure, specific fuel consumption, and brake torque) and estimates the factors influencing nitrogen oxides (NOx) formation for algae biofuel-diesel blends (A-diesel). The analyses were done using a thermodynamic model and simulated with Diesel-RK and ANSYS. The numerical results of Diesel-RK and ANSYS were validated with experimental in-cylinder pressure data, and also compared with existing literature where needed. Injection timing, engine speed, and inlet temperature were selected as variables for developing the model. The engine speeds were chosen from 1400 rpm to 2500 rpm, and the injection timings were varied from 30° Before Top Dead Center (BTDC) to 20° After Top Dead Center (ATDC). Three algae biofuel blends such as 5% Algae-oil and 95% diesel (A5), 10% Algae-oil, and 90% diesel (A10), 15% Algae-oil and 85% diesel (A15), and pure diesel were considered as fuels for the analysis. The numerical findings indicate that higher inlet temperature, in-cylinder combustion temperature, and advanced injection timing are the main reasons for higher NOx formation during combustion. Among all the four fuels, algae bio-fuel blends showed lower NOx formations than conventional diesel fuel, and also, the engine performance was satisfactory. These two developed numerical models will also help researchers investigate various fundamental parameters of a diesel engine using blended fuels.

Investigation of major factors that cause diesel NOx formation and assessment of energy and exergy parameters using e-diesel blends

The study investigated the key factors that influence the formation of diesel nitrogen oxides (NOx) ethanol–diesel (e-diesel) blends. In the first phase of this investigation, a thermodynamic model was developed to simulate and analyse the different parameters that affect the NOx formation. GT-Power was used to develop the model. ANSYS was also used to compare the results of GT-Power. The simulated (GT-Power and ANSYS) data of cylinder pressure was validated with experimental in-cylinder pressure data. For the 1-D model development, a 4-cylinder diesel engine with a compression ratio of 22.6 was chosen. The engine speed was differed from 1400 rpm to 2400 rpm; the injection timing was varied from 30° before top dead centre (BTDC) to 20° after top dead centre (ATDC), the inlet air temperature were changed from 293 K to 393 K, and the injected masses were ranged from 32 mg to 92 mg. Also, the energetic and exergetic parameters with respect to oxygen ratio and equivalence ratio were investigated. For this investigation, three ethanol blends and neat diesel fuel were used. The first blend was prepared with 10% ethanol and 90% diesel (E10), Similarly, the E20, E30 were made. The simulated data indicated that higher in-cylinder combustion temperature, inlet temperature, injected mass, and advanced injection timing were the principal causes for higher NOx formation. Interesting to note that among the four fuels, all three blends showed less NOx relative to neat diesel. The energy and exergy parameters with oxygen ratio show insignificant variations among the four fuels.

Effects of Combustion Parameters on Emissions of Diesel, Diesel/n-Butanol, and Diesel/n-Butanol/2-Ethylhexyl Nitrate Fuels at Different Intake-Oxygen Concentrations in a Diesel Engine

This paper tested one cylinder of a modified light-duty 4-cylinder diesel engine to study the coupling effect of 1.8-bar pressure and oxygen concentration (Coxy) on the combustion process of diesel (B00), diesel/n-butanol (B20) and diesel/n-butanol/2-ethylhexyl nitrate (B20+EHN), with emphasis on the analysis of the influence of combustion state parameters on emission generation. The research results showed that the difference between B00 fuel and B20 fuel in hydrocarbon (HC) and CO emissions was caused mainly by the combustion duration (CD) when the gas circuit concentration was 12%–17%, whereas when the gas circuit Coxy was 9%–12%, the HC and CO emissions were the result of the combined action of the two factors of in-cylinder combustion temperature (IT) and CD. The main influencing factor of NOx emission difference was IT. However, the main influencing factor of soot emission difference at 11%–17% gas circuit Coxy was the ignition delay period (ID), and at 9%–11% gas circuit Coxy it was the in-cylinder combustion temperature. Further research on the emissions difference between B00 fuel and B20+EHN fuel showed that ID plays a decisive role in the reduction of HC and CO emissions.

Experimental study on the effects of the Miller cycle on the performance and emissions of a downsized turbocharged gasoline direct injection engine

The Miller cycle has been proven to be an effective way to improve the thermal efficiency for gasoline engines. However, it may show insufficient power performance at certain loads. In this study, the objective is to exploit the advantages of the Miller-cycle engines over the original Otto-cycle engines. Therefore, a new camshaft profile with early intake valve closure was devised, and two various pistons were redesigned to obtain higher compression ratio 11.2 and 12.1, based on the original engine with compression ratio 10. Then, a detailed comparative investigation of the effects of Miller cycle combined with higher compression ratio on the performance and emission of a turbocharged gasoline direct injection engine has been experimentally carried out based on the engine bench at full and partial loads, compared to the original engine. The results show that, at full load, for a turbocharged gasoline direct injection engine utilizing the Miller cycle, partial maximum power is compromised about 1.5% while fuel consumption shows a strong correlation with engine speed. At partial load, since the Miller effect can well reduce the pumping mean effective pressure, thus improves the fuel economy effectively. In addition, the suppression of the in-cylinder combustion temperature induced by the lower effective compression ratio contributes to the reduction of nitrogen oxide emission greatly. However, the total hydrocarbon emission increases slightly. Therefore, a combination of the Miller cycle and highly boosted turbocharger shows great potential in further improvement of fuel economy and anti-knock performance for downsized gasoline direct injection engines.

Assessment of atomized water injection in the intake manifold of a heavy duty diesel engine for NOx reduction potential

Diesel engines, since many years, have found their own market with their robustness, low manufacturing cost and high efficiency. Although diesel engines have so many advantages, they are being blamed for their high pollutant emissions. Main pollutants from diesel engine are NOx, CO, CO2, HC and PM. Out of these pollutants, CO, CO2, HC, and PM can be reduced using some after treatment system in the tail pipe. But NOx needs to be addressed within the cylinder which would reduce the cost of after treatment system. Since NOx formation is the function of high combustion temperature, this temperature should be reduced by some means. In this study, atomized water injection system was employed to reduce in-cylinder combustion temperature there by reducing NOx formation. Here, water was injected into the air-intake pipe along with the EGR stream. 1-D simulation model of the study engine was created using AVL BOOST. Three full load operating points were considered and simulations were performed for 2.8mg, 4mg and 6mg of water injection at each operating points. Performance and emission parameters were then validated with the test data. Results showed that increase in water injection quantity reduces NOx emission but increases the smoke value. 2.8mg of water injection was chosen to be optimum, which reduces about 90°C of in-cylinder temperature, 8-10% of NOx reduction and increases smoke by about 20% from base value.

Characterization of In-Cylinder Combustion Temperature Based on a Flame-Image Processing Technique

The analysis of in-cylinder combustion temperatures using flame image processing technology is reliable. This method can accurately, intuitively, and in real time obtain the temperature field distribution law of the combustion flame in the cylinder, so we can more deeply understand the characteristics of the combustion process of internal combustion engines. In this paper, a high-speed charge-coupled device (CCD) camera is used to record an in-cylinder combustion image, which is calculated and corrected according to the principle of three primary color temperature measurement, and the temperature field distribution of the combustion flame in the diesel engine cylinder is analyzed in detail. In addition, the temperature of the typical combustion flame images under the open-cycle and closed cycle conditions is compared by the CMS2002 measurement and MATLAB program, respectively. The results show that the accuracy of the MATLAB program is acceptable in general but not entirely acceptable in a few ways.

Emission characteristics and engine performance of gasoline DICI engine in the transition from HCCI to PPC

The injection strategy is commonly manipulated to control the stratification level to simultaneously achieve a low pollutant emission and a high efficiency in internal combustion engines. This paper reports on a joint experimental and numerical study of the emission characteristics and engine performance in a heavy-duty direct-injection compression ignition (DICI) engine operating in the HCCI and PPC regimes, with a primary reference fuel made up of iso-octane (81% by volume) and n-heptane (19%) as a model gasoline fuel. The injection timing was varied to achieve different levels of stratification of the charge in the cylinder while the intake air temperature was adjusted accordingly to keep the same combustion phasing at 3° crank angle (CA) after top dead centre (ATDC). The main results of the present study are: (1) In gasoline DICI engines, the fuel is injected into the cylinder at an earlier SOI. The combustion process can be divided into different regimes, HCCI, PPC, and transition from HCCI to PPC, depending on SOI. Two distinctive classes of in-cylinder combustion temperature distributions could be found from the simulation results for the studied engine: one was for the SOI range from -100 to -48 °CA ATDC, which was the HCCI regime and/or the transition from HCCI to PPC regime, where the mean effective in-cylinder temperature was lower than 1700 K. The second class was for the SOI range from -44 to -20 °CA ATDC, where the combustion temperature was higher than 1850 K. This corresponded to the PPC regime. (2) The NOx emission was not only affected by the mean temperature but also the distribution of temperature in the cylinder. (3) The main source of unburned hydrocarbon (UHC) emission in the HCCI and the transition regimes was the fuel trapped in the crevice region where the oxidation process could not function properly. (4) Carbon monoxide (CO) emissions showed a non-monotonic variation with the injection timing, with one peak forming in the bowl region and one forming in the squish region during the transition from HCCI to PPC. The main source of CO emission was in the low temperature and fuel-lean region in the cylinder. (5) In the present engine operation, the pressure rise rate (PRR) in the PPC regime was higher than that in the HCCI regime, which is contrary to most results reported in the literature. This is a combined effect of low equivalence ratio in the piston bowl and in the squish region, and the stratification of the ignition delay time in the mixture. (6) Highest thermodynamic efficiency was achieved in the PPC regime with SOI from -44 to -31 °CA ATDC. In the transition from HCCI to PPC regime, the thermodynamic efficiency reached its lowest due to the poor combustion efficiency.

Experimental Study of the Effect of Intake Oxygen Concentration on Engine Combustion Process and Hydrocarbon Emissions with N-Butanol-Diesel Blended Fuel

This paper summarizes a study based on a modified, light, single-cylinder diesel engine and the effects of the physicochemical properties for n-butanol-diesel blended fuel on the combustion process and hydrocarbon (HC) emissions in the intake at a medium speed and moderate load in, an oxygen-rich environment (Coxy = 20.9–16%), an oxygen-medium environment (Coxy = 16–12%), and an oxygen-poor environment (Coxy = 12–9%). The results show that the ignition delay period is the main factor affecting the combustion process and it has a decisive influence on HC emissions. In an oxygen-medium environment, combustion duration affected by the cetane number is the main reason for the difference in HC emissions between neat diesel fuel (B00) and diesel/n-butanol blended fuel (B20), and its influence increases as the intake oxygen concentration decreases. In an oxygen-poor environment, in-cylinder combustion temperature affected by the latent heat of vaporization is the main reason for the difference in HC emissions between B00 and B20 fuels, and its influence increases as the intake oxygen concentration decreases. By comparing B20 fuel with diesel/n-butanol/2-ethylhexyl nitrate blended fuel (B20 + EHN), the difference in the ignition delay period caused by the difference in the cetane number is the main reason for the difference in HC emissions between B20 and B20 + EHN fuels in oxygen-poor environment, and the effect of this influencing factor gradually increases as the intake oxygen concentration decreases.

Influence of coupling action of oxygenated fuel and gas circuit oxygen on hydrocarbons formation in diesel engine

In this paper, by comparing the effect of three fuels (B0, B20 and B20 + EHN) on engine hydrocarbon (HC) emissions in different oxygen concentrations, the relationship between the HC formation and the coupling effect of three factors: the fuel oxygen content, the combustion duration and the in-cylinder combustion temperature was analyzed. The result shows that the combustion temperature is the main influencing factor of HC emissions in the oxygen-enriched environment. However, in the medium-oxygen and oxygen-deficient environments, the fuel oxygen content factor has a greater effect than the combustion temperature. In view of the difference between the B20 fuel and the B20 + EHN fuel on HC emissions, the influence of the combustion duration on the HC emissions is much greater than that of the combustion temperature and with the decrease of the oxygen concentration, the influence weight of the combustion duration is weakened. In addition, the HC emissions from the B0 and the B20 fuels were compared. The result shows that the combustion duration is the main factor for HC emissions reduction, and the influence weight of the factor of combustion duration is greater than the sum of the oxygen content in the fuel and the combustion temperature.

Effect of cooled EGR on modified light duty diesel engine for combustion, performance and emissions under high pressure split injection strategies

Environmental concerns demands light duty Engines to satisfy the stringent Euro VI emission norms. The aim of this study is to present the effect of cooled exhaust gas recirculation (EGR) on emission reduction. Tests are conducted on a modified single cylinder light duty diesel engine to run on high pressure common rail direct fuel injection. Diesel is injected directly in to the engine cylinder for both retarded and split injections at pressures of 200, 230, 250, 300 and 350 bar respectively. Cooled EGR is circulated along with intake air in to the inlet manifold of the engine for flow rates of 5% and 10%( wt/wt) of injected air respectively for both retarded and split injections. Single injection is retarded at − 11° ATDC and split injection consists of pilot injection at − 54°ATDC of 10% mass share and main injection at − 11°ATDC of 90% mass share. The result shows split injection (MPFI) decreases the ignition delay, In-cylinder combustion temperature and peak pressure for higher EGR flow rates compared to retarded single injection (SI) for all Injection pressure. Split injection reduced NOx from 1400 ppm to 200 ppm for 10% EGR flow rate at 350 bar injection pressure at full load operating conditions. Split injection at high Injection pressure decreases smoke by 10% as compared to retarded single injection. Test results show that there is trade-off exists between retarded and split injections at 350 bar injection pressure at full load conditions. Retarded injection has 33.61% brake thermal efficiency while split injection exhibits only 29.06% for 5% EGR flow rates. But higher EGR flow rates of 10% both retarded and split injection has nearly same brake thermal efficiency of 30.11%. Split injection reduced the combustion duration, ignition delay and exhaust gas temperatures for higher EGR flow rates compared to single retarded injection. The present research reveals that there exists an injection pressure map between the design operating pressure and maximum injection pressure. MPFI system under CRDI mode is very effective in reducing the NOx emissions with 10% EGR flow rates for maximum Injection pressure. While retarded SI injection is effective for moderate Injection pressure with the same EGR flow rates.

Exploring alternative combustion control strategies for low-load exhaust gas temperature management of a heavy-duty diesel engine

The employment of aftertreatment systems in modern diesel engines has become indispensable to meet the stringent emissions regulations. However, a minimum exhaust gas temperature of approximately 200 °C must be reached to initiate the emissions control operations. Low-load engine operations usually result in relatively low exhaust gas temperature, which lead to reduced or no exhaust emissions conversion. In this context, this study investigated the use of different combustion control strategies to explore the trade-off between exhaust gas temperature, fuel efficiency, and exhaust emissions. The experiments were performed on a single-cylinder heavy-duty diesel engine at a light load of 2.2 bar indicated mean effective pressure. Strategies including the late intake valve closing timing, intake throttling, late injection timing (Tinj), lower injection pressure (Pinj), and internal exhaust gas recirculation and external exhaust gas recirculation were investigated. The results showed that the use of external exhaust gas recirculation and lower Pinj was not effective in increasing exhaust gas temperature. Although the use of late Tinj could result in higher exhaust gas temperature, the delayed combustion phase led to the highest fuel efficiency penalty. Intake throttling and internal exhaust gas recirculation allowed for an increase in exhaust gas temperature at the expense of higher fuel consumption. In comparison, late intake valve closure strategy achieved the best trade-off between exhaust gas temperature and net indicated specific fuel consumption, increasing the exhaust gas temperature by 52 °C and the fuel consumption penalty by 5.3% while reducing nitrogen oxide and soot emissions simultaneously. When the intake valve closing timing was delayed to after −107 crank angle degree after top dead centre, however, the combustion efficiency deteriorated and the HC and CO emissions were significantly increased. This could be overcome by combining internal exhaust gas recirculation with late intake valve closure to increase the in-cylinder combustion temperature for a more complete combustion. The results demonstrated that the ‘late intake valve closure + internal exhaust gas recirculation’ strategy can be the most effective means, increasing the exhaust gas temperature by 62 °C with 4.6% fuel consumption penalty. Meanwhile, maintaining high combustion efficiency as well as low HC and CO emissions of diesel engines.

Numerical simulation and experimental research on combustion characteristics of compression-ignition engine under an O2/CO2 atmosphere

ABSTRACTThis study investigates the combustion characteristics of compression-ignition engines under an O2/CO2 atmosphere, through numerical simulation and experimental analysis methods, which will eventually provide a new solution of the “NOx-Soot” trade-off problem. The computational fluid dynamics (CFD) software FIRE is adopted to simulate in-cylinder combustion temperature and pressure, according to different O2 volume ratio and different ignition advance angle. The dyno test including visualisation diagnostic is carried out under the above gas composition so that the emission and combustion characteristics can be analysed.The simulation results of engine power performance show that when the ignition advance angle remains unchanged compared to the baseline engine, a combination of 65% O2 with 35% CO2 is the recommended gas composition. And the in-cylinder peak pressure of the engine is about 6.66 MPa, which is equivalent to that when the engine runs at normal air intake conditions. The results of the ...

Pre-injection strategy for pilot diesel compression ignition natural gas engine

For pilot fuel compression ignition natural gas (CING) engine, pre-injection strategy of pilot fuel is an important ways to improve engine performance, emissions and combustion. In this study, effects of pre-injection parameters on combustion and emissions performance were experimentally studied in a pilot diesel CING engine which was modified from a turbocharged six-cylinder diesel engine. The cylinder pressure, heart release rate (HRR), start of combustion (SOC), duration of combustion (DOC) and coefficient of variation (COVIMEP), as well as NOx and HC emissions were analyzed. The results indicate that early pre-injection mode leads to lower cylinder pressure and HRR due to decrease of combustion intensity, and thereby lower NOx emission is obtained. In contrast, closely pre-injection timing leads to largely strengthening in combustion which is not beneficial for improving NOx emission performance.Furthermore, effects of pre-injection quantity ratio and fuel injection pressure on combustion and emissions of early pre-injection operation modes (on pre-injection timing of 70°CA BTDC) were analyzed. Increase of pre-injection quantity ratio leads to decreasing in ignition intensity which delayed SOC and slowed burning rate of in-cylinder mixture, and thereby leads to lower cylinder pressure and HRR. Due to slowing in in-cylinder combustion, combustion temperature decreased, and hence leads to lower NOx emission and higher HC emission. However, too high pre-injection quantity ratio leads to unstable ignition and even unstable combustion which is not beneficial for engine performance. Increasing fuel injection pressure leads to larger fraction of premixed quantity of injected fuel which increased ignition energy and leads to rapid combustion, and hence higher cylinder pressure and HRR were obtained. Due to the increase of burning rate of in-cylinder mixture, in-cylinder combustion temperature was increased, and hence leads to higher NOx emission and lower HC emission.

Emissions and fuel consumption characteristics of an HCNG-fueled heavy-duty engine at idle

The idle performance of an 11-L, 6-cylinder engine equipped with a turbocharger and an intercooler was investigated for both compressed natural gas (CNG) and hydrogen-blended CNG (HCNG) fuels. HCNG, composed of 70% CNG and 30% hydrogen in volume, was used not only because it ensured a sufficient travel distance for each fueling, but also because it was the optimal blending rate to satisfy EURO-6 emission regulation according to the authors' previous studies. The engine test results demonstrate that the use of HCNG enhanced idle combustion stability and extended the lean operational limit from excess air ratio (λ) = 1.5 (CNG) to 1.6. A decrease of more than 25% in the fuel consumption rate was achieved in HCNG idle operations compared to CNG. Total hydrocarbon and carbon monoxide emissions decreased when fueled with HCNG at idle because of the low carbon content and enhanced combustion characteristics. In particular, despite hydrogen enrichment, less nitrogen oxides (NOx) were emitted with HCNG operations because the amount of fuel supplied for a stable idle was lower than with CNG operations, which eventually induced lower peak in-cylinder combustion temperature. This low HCNG fuel quantity in idle condition also induced a continuous decrease in NOx emissions with an increase in λ. The idle engine test results also indicate that cold-start performance can deteriorate owing to low exhaust gas temperature, when fueled with HCNG. Therefore, potential solutions were discussed, including combustion strategies such as retardation of spark ignition timing combined with leaner air/fuel ratios.