Hot Start Conditions Research Articles

Exploiting Lubricant Formulation to Reduce Particle Emissions from Gas Powered Engines

The present paper illustrates the results of an experimental study aimed at evaluating the effect of lubricant oil features on the emissive behaviour of a heavy duty spark ignition engine fuelled with methane. The activity was performed within a research project between CNR-STEMS and TotalEnergies in which oils with different formulations were characterized, focusing on their potentiality in particle emission reduction. Considering the ultralow particle emission level in the exhaust of gas engines, a specific testing procedure was designed to guarantee highly reliable and accurate results. In particular, the engine was operated under transient conditions, along the World Harmonized Transient Cycle in cold- and hot-start conditions. The results of the test campaign clearly highlight that the lubricant formulation is a key technology for the control of particles, revealing this as an important aspect in view of the upcoming severe regulation limits on particle emissions. The experimental findings show the capability of reformulated oils to drop down the total particle number to 60–70% with respect to a baseline standard oil. The interest in the present study also lies in providing information extendable to more sustainable fuels, like hydrogen or biomethane, nowadays of great interest as alternative energy sources.

Experiments and modeling of the thermal spray-chasing phenomenon during split injection processes

Spray chasing is a specific manifestation of the interaction between split injections, where the mass and heat transfer between the pilot and main sprays significantly influence fuel mixing and ignition processes. In this study, a spray-chasing model is developed and validated based on optical diagnostic results, aiming to theoretically support the development of injection strategies that are more environmentally adaptive and offer improved performance. A series of optical diagnoses of diesel split injection is performed in a constant volume combustion chamber using diffused back-illumination imaging and high-speed schlieren imaging. The extent of the spray-chasing phenomenon is modulated by regulating the injection dwell time (DT) and ambient temperature. For inert sprays, when the background temperature exceeds 790 K, the liquid spray-chasing phenomenon can be disregarded owing to the premature evaporation of the pilot spray. Although shortening the DT can promote the development and mixing of the main spray, the lack of evaporation in the pilot fuel pocket leads to a higher local fuel concentration in the interaction zone after spray chasing, which will hinder the subsequent ignition of the main spray. For reactive sprays, the variations in spray chasing patterns under different operating parameters are determined and their impact on the ignition process is evaluated by combining optical test results with theoretical models. Under cold start conditions, the ignition delay and ignition location of the main spray exhibit a non-monotonic trend with increasing injection dwell time. Optical diagnosis observes that compared to DT of 200 us and 1500 μs, the main spray exhibits both valley in ignition delay time and ignition location at DT = 900 μs. The spray-chasing model identifies approximately 1020 μs as the optimal theoretical DT, expected to best facilitate ignition of the main spray. However, under hot-start conditions, even though the spray-chasing mode varies with different injection dwell times, the ignition characteristics remain essentially unchanged due to the limited promotion effect of split injection on ignition.

Characterizing ammonia emission from light-duty gasoline vehicles under the influence of multiple factors and its correlation with conventional pollutants

Ammonia (NH3), which is a precursor of secondary particulate matter (PM), can be produced through three-way catalyst (TWC) side reactions in light-duty gasoline vehicles (LDGVs), posing a threat to human health and air quality. To explore ammonia emission characteristics, 8 LDGVs and 1 hybrid electric light-duty vehicle (HEV) with various mileages traveled were analyzed with a chassis dynamometer system during regulation driving cycles. The emission factors of the adopted China VI in-use LDGVs were 7.04 ± 2.61 mg/km under cold-start conditions and 4.94 ± 1.69 mg/km under hot-start conditions. With increasing mileage traveled, the total ammonia emissions increased, and the difference between the cold/hot-start results decreased. The emissions of in-use LDGVs with bi-fuel engines were analyzed, and more ammonia was generated in the compressed natural gas (CNG) mode through the hydrocarbon (HC) reforming reaction. The relationship between the emissions of ammonia and conventional pollutants was established. During the initial cold-start phase, a delay in ammonia formation was observed, and the ammonia emissions conformed with the CO and HC emissions after exhaust heating. Vehicle specific power (VSP) analysis revealed that the interval of highest ammonia emissions corresponded to acceleration events at high speeds. For the HEV, the transition from motor to engine drive conditions contributed to ammonia emission occurrence because of the more pronounced cold-start events. The use of HEV technology could introduce additional uncertainties in controlling urban ammonia emissions. Detailed analysis of emission characteristics could provide data support for future research on ammonia emission standards and control strategies for LDGVs.

Investigation of the dynamic interaction mechanism of split injections during the ignition process under diesel engine-like cold- and hot-start conditions

In a range of operating conditions with variable injection parameters, interactions among split sprays present uncertainties across both temporal and spatial dimensions. Understanding these dynamic interactions is crucial for optimizing injection strategies to improve both the performance and environmental adaptability of diesel engines. In this study, optical diagnostics and numerical simulations were conducted to explore the interaction mechanisms between split injections and their impact on the ignition process. Engine-like cold and hot-start operating conditions were configured, and four injection strategies, including a single injection, were examined. The findings reveal that ambient temperature influences split spray interactions by altering their ignition characteristics, while injection dwell time modifies these interactions by changing the combustion spatial and temporal phase between split sprays. Compared to a single injection, split injection promotes the ignition and combustion of the main spray such as shortening ignition delay, reducing ignition location, and increasing flame area, but this promoting effect weakens under hot-start conditions. When the main spray chases the pilot spray before ignition, it increases the local concentration and reduces the temperature upstream of the pilot spray plume. However, since the effect front fails to reach the expected ignition region before the pilot ignition occurs, the ignition of the pilot fuel pocket remains unaffected. Under cold-start conditions, the main ignition delay shows a non-monotonic trend, reaching its minimum at an injection dwell of 900 μs, where the pilot ignition provides the main spray with elevated local temperatures and an increased hydroxyl mass fraction. Under hot-start conditions, the temporal overlap of ignition in split sprays is enhanced, yet spatial interaction weakens. Despite varying degrees of pilot flame decay before the main spray ignites with increasing injection dwells, the thermal radiation emanating from their combustion elevates the local temperature in the interaction zone beyond 1200 K. Consequently, upon catching up with the pilot injection, the main spray mixture rapidly ignites through the high-temperature reaction pathway, rendering the ignition delay insensitive with injection dwells.

Design of A Portable Solid-Fuel Rocket Stove

The depletion of fossil fuels is a hot topic of discussion these days. This is due to the increasing use of fossil fuels in human life. In terms of the increase in fuel and gas prices, we realise that the energy consumption that is increasing from year to year is not balanced with the availability of energy sources, which affects households that use fuel in the cooking process. So a design was carried out to make an ergonomic solid fuel stove with the aim of not using fuel anymore in the cooking process, in this design, the stove is designed to be more flexible and get a portable biomass rocket stove design by considering social aspects, performance, local resources, economy, environmentally friendly. Biomass fuels are solids, liquids or gases produced from organic matter.. Biomass fuels used in solid fuel stoves such as firewood, charcoal, briquettes and pellets. Each biomass fuel has different properties and characteristics. The designed portable rocket stove consists of several main parts namely combustion chamber, chimney, air duct, pan spot and cassing, using stainless steel material. The test results include combustion chamber and water temperature during the process, thermal efficiency, combustion rate and specific fuel consumption under cold start and hot start conditions. After hot start, it is found that the use of a chimney on a portable stove designed using coconut shell fuel is more effective than without a chimney. Shorter boiling time of 1 minute, greater combustion rate of 0.13 grams/minute, higher thermal efficiency of 2% and lower specific fuel consumption of 9.11 grams/litre of water when the stove uses a chimney.

An assessment of the application of catalyst preheating prior to engine cold start to improve the filtration performance of CDPF on particulate emissions

The catalytic diesel particulate filter (CDPF) is an effective technology for reducing particle emissions. However, during engine startup, especially in cold start conditions, notable particle emissions are observed at the CDPF outlet. These emissions are attributed to combustion deterioration during startup and the low temperature of the aftertreatment catalyst. Addressing this challenge, this study investigated the effectiveness of rapidly preheating the diesel oxidation catalyst (DOC) and CDPF substrate temperatures before engine start to enhance particle removal during cold starts. Experimental results indicated that CDPF filtration efficiency during cold start was lower compared to hot start conditions, with a clean CDPF exhibiting very low efficiency due to minimal particle deposition. Substrate temperature preheating of either the DOC or CDPF was found to improve CDPF filtration efficiency for particles during cold start, albeit with a concurrent increase in emissions of particles smaller than 50 nm. Notably, a combination of a 250 °C DOC with a 22 °C CDPF yielded the most significant reduction in particle emissions, particularly for particles under 50 nm. Given that the DOC shares the same material composition as the CDPF but has a smaller volume that requires less energy for heating, preheating the DOC emerges as a more energy-efficient strategy. These findings underscore the need for more comprehensive studies on catalyst preheating to further the commercialization of technologies that effectively reduce cold start particle emissions, aligning with increasingly stringent future emission regulations.

Thermally controlled intein splicing of engineered DNA polymerases provides a robust and generalizable solution for accurate and sensitive molecular diagnostics.

DNA polymerases are essential for nucleic acid synthesis, cloning, sequencingand molecular diagnostics technologies. Conditional intein splicing is a powerful tool for controlling enzyme reactions. We have engineered a thermal switch into thermostable DNA polymerases from two structurally distinct polymerase families by inserting a thermally activated intein domain into a surface loop that is integral to the polymerase active site, thereby blocking DNA or RNA template access. The fusion proteins are inactive, but retain their structures, such that the intein excises during a heat pulse delivered at 70-80°C to generate spliced, active polymerases. This straightforward thermal activation step provides a highly effective, one-component 'hot-start' control of PCR reactions that enables accurate target amplification by minimizing unwanted by-products generated by off-target reactions. In one engineered enzyme, derived from Thermus aquaticus DNA polymerase, both DNA polymerase and reverse transcriptase activities are controlled by the intein, enabling single-reagent amplification of DNA and RNA under hot-start conditions. This engineered polymerase provides high-sensitivity detection for molecular diagnostics applications, amplifying 5-6 copies of the tested DNA and RNA targets with>95% certainty. The design principles used to engineer the inteins can be readily applied to construct other conditionally activated nucleic acid processing enzymes.

Effect of idle-start-go on the economy and emissions of gasoline vehicles

The idle start-go (ISG) system has been widely used, but there have been few relevant studies of its effect on emissions. This paper investigates fuel economy, total hydrocarbon (THC), carbon monoxide (CO), nitrogen oxides (NOx), particulate mass (PM), and particle number (PN) emissions from China VI gasoline direct injection (GDI) vehicles with and without ISG. Three test cycles were performed under hot start conditions, that is, the worldwide harmonized light vehicle test cycle (WLTC), the China light-duty vehicle test cycle (CLTC), and the USA federal test procedure-75 (FTP-75). About 28 idling phases were selected to specifically analyze the influence of ISG system. The results reveal that ISG system helps decrease fuel consumption, THC and CO emissions but aggravates NOx and solid PN emissions. Also, ISG system increases the proportions of sub-23 nm and nucleation-mode particle emission. Idling time plays a role in fuel economy, THC and CO emissions, while accelerated speed affects the emissions of THC, CO, NOx, and PN.

Comprehensive characterization of polycyclic aromatic hydrocarbon emissions from heavy-duty diesel vehicles utilizing GC × GC-ToF-MS

Comprehensive characterization of diesel vehicle emitted polycyclic aromatic hydrocarbon (PAH) emissions is yet to achieve due to the limitation of analytical methods. Therefore, we herein developed a two-dimensional gas chromatography time-of-flight mass spectrometry (GC × GC-ToF-MS) method and quantified the total PAHs from diesel vehicles based on their characteristic fragments and mass spectral patterns. Overall, the emission factors (EFs) of total PAHs (gas + particle) are observed to range from 4.1 ± 2.5 mg km−1 to 51.4 ± 22.2 mg km−1 under cold-start and hot-start conditions for one China IV and two China VI heavy-duty diesel vehicles (HDDVs), of which the un-speciated PAHs account for more than 97%. Gaseous PAHs (g-PAHs) are dominated by three-ring PAHs, whereas particulate PAHs (p-PAHs) are dominated by two-ring PAHs. The total PAHs partition significantly into the gas phase for whole fleets and cycles, except that five-ring PAHs partition almost completely into the particle phase. The aftertreatment technologies (e.g., diesel particulate filter, DPF) significantly reduce the total PAH emissions by 49.8 ± 33.2%. The minimum toxic equivalency factors (TEFs) are deployed to estimate the toxicity of the total PAHs. Much higher toxicity is obtained than those in previous studies, indicating that the PAH toxicity of diesel vehicle emissions might be largely underestimated.

NOX emission analysis according to after-treatment devices (SCR, LNT + SCR, SDPF), and control strategies in Euro-6 light-duty diesel vehicles

This study used emission certification data for vehicles that met Korea's Euro-6 emission standards after 2018. It was analyzed that the distribution of nitrogen oxide (NOX) emission in accordance with the type of after-treatment system under cold and hot start conditions by classifying domestic and imported cars. In addition, the relationship between electronic control unit (ECU)/dosing control unit (DCU) signals and exhaust emissions were analyzed under NEDC and WLTP driving mode conditions. Three models of vehicles equipped with different after-treatment systems were selected among the vehicles subject to the 2019 real road driving test for this study. And it was acquired that ECU and DCU signals, which are expected to be related to emissions as well as emissions. In order to satisfy Euro-6, the LNT + SCR after-treatment system was applied to more than 76% of vehicle models. Among ECU signals, there was a direct relationship between the accelerator pedal and the EGR valve opening degree, and there was a deviation depending on the driving mode. Among the DCU signals, the catalyst temperature, urea-water injection quantity, and injection timing are controlled in accordance with the NOX emission measured by the sensor. In the future, it is necessary to analyze the correlation between the ECU signal and the DCU signal to derive a factor that can be used as a measure to suspect defeat devices.

Characterization of Particle Emissions of Turbocharged Direct Injection Gasoline Engine in Transients and Hot Start Conditions

Reducing pollutant emissions, particularly soot particles emitted by internal combustion engines, is a major challenge for car manufacturers. In this paper, the experimental setup is a turbocharged three-cylinders gasoline direct injection engine installed on a HORIBA dynamic test driven by a HORIBA STARS computer. The particle-measuring device is a Pegasor Particles Sensor that measures the current carried by previously electrically charged particles. The hot engine stabilized tests, with lambda parameter lower or equal to one, have very low emission levels, unlike dynamic tests. As a consequence, the present paper deals with experiments in transient conditions. Unlike diesel engine, cycle tests show that particulate emissions vary widely. To understand the phenomenon, a simple transient was created and reproduced a hundred times in order to obtain enough data to analyze and compare these different tests. This transient starts from idle to reach the speed of 2000 r/min and 60 N.m in 5 s. To reach this point, it is necessary to stay in full load for about 3 s. The maximum deviations of particles reaches 85% with the standard deviation σ=18%. The cylinder pressure sensor shows significant variations at the very beginning of each transient, i.e., during the first 500 ms. This kind of result was observed for Worldwide harmonized Light vehicles Test Cycles (WLTC) with a maximum deviations of particles reaching 75% with σ=30%, on Real Drive Emissions Cycle (RDE) with a maximum deviations of particles reaching 45% with σ=22% and for a 300 s Mini-Cycle with a maximum deviations of particles reaching 70% with σ=17%. The Mini-cycle is made up of the five largest accelerations of the WLTP cycle. A complete analysis highlights the importance of filling the first engine cycles. This depends on the opening speed of the throttle, the position of the crankshaft at the beginning of the transient, and the acceleration of the first cycles. But, the NOx sensor shows very slight variations between each test. As a consequence, it appears that the variation of particles emissions is not only related to variation of equivalence ratio but with another setting, which may be the oil consumption. Finally, from these results, it is possible to determine a particle characterization function. It consists of two functions. The first one is the average of the emitted particles level which depends on the engine speed, engine acceleration, engine torque and torque acceleration. The second function, which corresponds to dynamic variations in emissions, mainly depends on oil consumption in the cylinder and on the combustion quality of the first transient engine cycles.

Effect of Using Nanoparticle-based Diesel Fuel on Enhancement of Performance and Emissions of Diesel Engines

Background:The current research work reports an investigation of the effects of employing CuO and TiO2 nanoparticles as potential additives to refinery (petroleum) diesel fuel, in order to reduce the emissions of combustion process as well as to enhance the combustion process.Methods:Nanodiesel samples were prepared with various concentrations (50 ppm, 100 ppm, 200 ppm, 300 ppm). The experimental work was conducted using a four stroke diesel engine with a single cylinder at various loads in order to accurately determine the influence of nanoparticles on combustion process. The experimental readings were measured at two conditions, cold start and hot start relative to the engine.Results:It was clearly observed that the nanodiesel fuels have significantly reduced CO, CO2, NO, unburned HC, and enhanced the engine performance. According to the experimental results the 100 ppm TiO2 and 200 ppm CuO nanodiesel have showed almost the highest performance and lowest emissions comparable to neat diesel fuel and other nanodiesel samples. Owing to 100 ppm TiO2 on hot start conditions, it was found that the CO, CO2, NO, unburnt HC, exhaust temperature, and BSFC have been reduced by 41.4%, 37 %, 38.3%, 81%, 4.9%, and 20.5% respectively at maximum load. Meanwhile, the brake power, RPM and thermal efficiency have increased by 1.5%, 1% and 2.65% respectively.Conclusion:Eventually the stability of nanodiesel fuels were investigated. Accordingly, the stability of 100 ppm TiO2 and for 200 ppm CuO are 7 days and 3 days.

Assessing fuel consumption reduction in Revercycle, a reversible mobile air conditioning/ Organic Rankine Cycle system

Organic Rankine Cycle (ORC) is a promising solution to improve vehicle efficiency, but its commercial success is hindered by the compactness and cost requirements of the automotive sector. In an attempt to overcome these limitations, a reversible mobile air conditioning (MAC)/ORC, hereafter called ReverCycle, is proposed in this work. ReverCycle is a compact system that operates in two different modes: a standard MAC system when cabin cooling is required or an ORC recovering mechanical energy from the waste heat of an engine’s cooling system.This study presents a simulation methodology to assess the ReverCycle fuel consumption gain. A global light duty vehicle model allows the estimation of the yearly working hours for each ReverCycle operating mode and quantifies the recovered mechanical energy in ORC mode. The ORC module is validated with experimental results. Validation has shown a normalized root-mean-square deviation between 5% and 11% for the main ORC variables (pressures, temperatures and electric powers).The average fuel consumption reduction in ReverCycle was 1.3 and 2% with cold start and hot start conditions, respectively. The reversible system lost 25% of the ORC waste heat recovery potential owing to MAC activation time; however, the significant reductions in cost and compactness were advantageous.

Behavior of the random-field XY model on simple cubic lattices at h_{r}=1.5.

We have performed studies of the three-dimensional random-field XY model on 32 samples of L×L×L simple cubic lattices with periodic boundary conditions, with a random field strength of h_{r} = 1.5, for L= 128, using a parallelized Monte Carlo algorithm. We present results for the sample-averaged magnetic structure factor S(k[over ⃗]) over a range of temperature, using both random hot start and ferromagnetic cold start initial states, and k[over ⃗] along the [1,0,0] and [1,1,1] directions. At T= 1.875, S(k[over ⃗]) shows a broad peak near |k[over ⃗]|=0, with a correlation length which is limited by thermal fluctuations, rather than the lattice size. As T is lowered, this peak grows and sharpens. By T= 1.5, it is clear that the correlation length is larger than L= 128. The lowest temperature for which S(k[over ⃗]) was calculated is T= 1.421875, where the hot start and cold start initial conditions usually do not find the same local minimum in the phase space. Our results are consistent with the idea that there is a finite value of T below which S(k[over ⃗]) diverges slowly as |k[over ⃗]| goes to zero. This divergence would imply that the relaxation time of the spins is also diverging. That is the signature of an ergodicity-breaking phase transition.

Inspection of PN, CO2, and Regulated Gaseous Emissions Characteristics from a GDI Vehicle under Various Real-World Vehicle Test Modes

Although the chassis dynamometer type approval test considers real-world conditions, there are a few limitations to the experimental test environment that may affect gaseous or particulate emissions such as road conditions, traffic, decreasing tire pressure, or fluctuating ambient temperature. Furthermore, the real driving emission (RDE) test takes a long time, and it is too long to repeat under different experimental conditions. The National Institute of Environmental Research (NIER) test modes that reflect the driving pattern of Korea are not certification test modes, but can be used to evaluate the influence of traffic conditions because these modes consist of a total of 15 test modes that vary according to average speed. The use of the NIER #03, #09, and #13 modes as low-, medium-, and high-speed modes allow for gaseous and particulate emissions to be measured and analyzed. Additionally, the worldwide harmonized light-duty vehicle test procedure (WLTP), the certification mode of Europe, is used to test cycles to investigate the difference under cold- and hot-engine start conditions. The engine operating parameters are also measured to evaluate the relationships between the various test conditions and test cycles. The regulated and greenhouse gas levels decrease under various driving conditions, but the particle number (PN) emission level shows a different trend with gaseous emissions. While the PN and CO2 results dramatically increase when the air conditioner is on, tire pressure conditions show different PN size distributions: a large-sized PN fraction, which contains particles larger than 100 nm, increases and a sub-23 nm-sized PN fraction decreases. Under cold-start conditions in the WLTP modes, there are much higher PN emissions than that of an engine under hot-start conditions, and the sub-23-nm-sized PN fraction also increases.

Investigation of Steam Turbine Warm-Keeping by Use of Air

AbstractThe changing energy landscape leads to a rising demand of more flexible power generation. A system for steam turbine (ST) warm-keeping provides the ability to shutdown conventional power plants during periods with a high share of renewable power. Simultaneously, these power plants are ready for grid stabilization on demand without an excessive consumption of lifetime during the start-up. One technical solution to keep a ST warm is the use of hot air, which is passed through the turbine. In addition, the air supply prevents corrosion during standstill and also enables the prewarming after maintenance or long outages. This paper investigates the warm-keeping process of an intermediate pressure (IP) ST (double-shell configuration) through the use of dynamic numerical finite element (FE) simulations. As a representative test case, warm-keeping calculations during a weekend shutdown (60 h) are conducted to investigate the temperatures, their distribution, and gradients within the rotor and the casing. For this purpose, an improved numerical calculation model is developed. This detailed three-dimensional FE model (including blades and vanes) uses heat transfer correlations conceived for warm-keeping with low air mass flows in gear mode operation. These analytical correlations take heat radiation, convection, and contact heat transfer at the blade roots into account. The thermal boundary conditions (BCs) at the outer walls of the rotor and casing are determined by use of experimental natural cool-down data. The calculation model is finally compared and verified with this dataset. The results offer valuable information about the thermal condition of the ST for a subsequent start-up procedure. The warm-keeping operation with air is able to preserve hot start conditions for any time period. Most of the heat is transferred close to the steam inlet of the turbine, which is caused by similar flow directions of air and steam. Thus, temperatures in the last stages and in the casing remain well below material limits. This allows higher temperatures at the first blade groove of the turbine, which is highly loaded during a turbine startup and thus crucial to the lifetime.

Energy and exergy efficiencies of four biomass cookstoves using wood chips

With the growing need for comprehensive analysis of energy conversion systems for performance evaluation and improvement, this study investigates the energy and exergy performance of four biomass cookstoves using wood chips as fuel source. The cookstoves evaluated include the three-stone fire, charcoal stove, modified charcoal stove, and top-lit updraft (TLUD) cookstove. The performance of the cookstoves was carried out following the standard cookstove testing protocol of water boiling test in cold and hot start conditions. Relevant parameters were measured at five-minute interval until the water reached the boiling temperature of 100 °C; the test was replicated four times for each stove and the mean value reported. The result of the study revealed that energy efficiency of the cookstoves was higher than the exergy efficiency both in the cold and hot start. The efficiencies increased steadily with time until the water reached 100 °C boiling temperature. The energy, and exergy efficiency in the cold and hot start condition of the cookstoves appear similar with no obvious difference; that is, the performance of the cookstoves appear the same irrespective of whether the stove is used in the cold or hot start condition. The TLUD cookstove offered better energy and exergy efficiencies compared to other cookstoves investigated.

Measurements of OC and EC Emission Factors for Light-duty Gasoline Vehicles

Organic carbon (OC) and elemental carbon (EC) emission factors from 27 State 3-5 light-duty gasoline vehicles (LDGVs) were tested in this study using a CVS (Constant Volume Sampling) system on a dynamometer. The influences of start conditions, driving cycles, and fuel injection technologies on the OC and EC emissions were analyzed. The results show that the OC emission factors of the tested State 3 to 5 LDGVs were (2.09±1.03), (1.59±0.78), and (0.75±0.31) mg·km-1, respectively, and the EC emission factors were (1.98±1.42), (1.57±1.80), and (0.65±0.49) mg·km-1. Both OC and EC emissions significantly decreased with the promotion of emission standards. The OC/EC ratios were 1.54±0.92, 1.53±0.91, and 1.47±0.66, respectively. OC1, OC2, EC1, and EC2 were the most important carbonaceous components from LDGVs, accounting for 15%, 20.6%, 22.2%, and 21.7%, respectively. OC and EC emission factors under cold-start conditions were 1.4 and 1.8 times those under hot-start conditions. OC and EC emission factors for highway cycles were 2 and 4 times those for urban cycles. OC emission factors from GDI (Gasoline Direct Injection) engines were close to those from PFI (Port Fuel Injection) engines. However, their EC emission factors were 1.7 times those from PFI engines. With the increasing popularity of GDI engines in LDGV fleets in China, the EC emissions from these engines should be paid more attention in the future.

Analysis of the repeatability of the exhaust pollutants emission research results for cold and hot starts under controlled driving cycle conditions

Measurement of car engines exhaust pollutants emissions is very important because of their harmful effects on the environment. This article presents the assessment of repeatability of the passenger car engine exhaust pollutants emission research results obtained in the conditions of a chassis dynamometer. The research was conducted in a climate chamber, enabling the temperature conditions to be determined from − 20 to + 30 °C. The emission of CO, CH4, CO2, NOX, THC, and NMHC was subjected to the analysis. The aim of the research is to draw attention to the accuracy of the pollutant emission research results in driving cycles, and the comparison of pollutant emission results and their repeatability obtained in successive NEDC cycles under cold and hot start conditions. The results of the analysis show that, in the case of a small number of measurements, the results repeatability analysis is necessary for a proper interpretation of the pollutant emission results on the basis of the mean value. According to the authors’ judgment, it is beneficial to determine the coefficient of variation for a more complete assessment of exhaust emission result repeatability obtained from a small number of measurements. This parameter is rarely presented by the authors of papers on exhaust components emission research.

Transient emission characteristics of a heavy-duty natural gas engine at stoichiometric operation with EGR and TWC

The recent issued emission regulations have more stringent standards for the transient emissions of natural gas engines. When equipped with cooled exhaust gas recirculation (EGR) and three way catalyst (TWC), natural gas engines operating at stoichiometric conditions are capable of achieving extremely low transient emissions. In this paper, the transient emission characteristics of a heavy-duty natural gas engine at stoichiometric operation with EGR and TWC are experimentally studied based on the world harmonized transient cycle (WHTC). The results show that both the raw carbon monoxide (CO) and total hydrocarbon (THC) emissions are higher in the hot start test while the raw NOx emissions are higher in the cold start test. When measurements are conducted after the TWC, all these emissions are higher in the cold start test. Among all the sub-cycles of WHTC, the urban sub-cycle plays the most important role for all three emissions in both cold start and hot start conditions except the after three way catalyst (ATWC) CO emissions in the cold start test, where the motorway sub-cycle takes up the highest percentage. In summary, CO, nitrogen oxide (NOx) as well as non-methane hydrocarbon (NMHC) emissions can meet the requirements of Euro VI emission standards, whereas CH4 emissions are higher than the corresponding standard, suggesting that improvements in the performance of the catalyst are essential.