Engine Cold Start Research Articles

Experimental study on the cerium oxide nanoparticles doped in diesel fuel improving the cold start performance of diesel engines at high-altitude and low-temperature environments

CeO2 nanoparticles are effective fuel additives that enhance fuel spray, atomization, and combustion characteristics due to their high catalytic activity and excellent thermal properties. When added to fuel, CeO2 nanoparticles significantly improve in-cylinder combustion, and engine performance, and reduce pollutant emissions under normal engine operating conditions. Diesel engines encounter persistent challenges during cold starts at low temperatures and high altitudes. However, there is limited research on the effects of CeO2 nanoparticles on ignition and combustion at low temperatures and cold start performance. This study aims to evaluate the impact of CeO2 nanoparticles doping in diesel fuel on the cold start performance of diesel engines in high-altitude and low-temperature environments. Diesel fuel doped with CeO2 nanoparticles at various concentrations was prepared using magnetic stirring and ultrasonication. The cold start performance of the test engine was assessed in an environmental chamber. This work investigated and evaluated the improvements of CeO2 nanoparticles on cold start performance from three perspectives: general low-temperature conditions, high-altitude environments, and extreme low-temperature scenarios with diethyl ether premixing. Experimental results indicate that incorporating CeO2 nanoparticles expanded the critical temperature required for a successful cold start from 0 °C to −5 °C. At high altitudes, the addition of CeO2 nanoparticles effectively increased the proportion of efficient combustion, evidenced by single peak and parent peak patterns during cold starts. CeO2 nanoparticles facilitated the transition from low-temperature to high-temperature reactions, promoting fuel ignition during the first injection cycle and reducing speed fluctuations during cold starts with diethyl ether premixing at −40 °C. Furthermore, adding CeO2 nanoparticles prevented detonation and rapid pressure surges during cold starts. Overall, doping diesel fuel with CeO2 nanoparticles proves to be an effective method for enhancing cold start performance in diesel engines. This study offers a novel approach for improving diesel engine cold start performance in high-altitude and low-temperature conditions.

Bidirectional circulating preheating method harnessing engine and battery waste heat reuse in hybrid electric vehicles

In hybrid electric vehicles (HEVs), both the engine and power batteries experience reduced performance at low temperatures, necessitating the consumption of significant energy for preheating. The bidirectional preheating system method, which for the first time applies waste thermal energy to preheat both the engine and power battery in HEVs, utilizes the engine’s residual thermal energy to preheat the power battery and the thermal energy from the power battery to preheat the engine. To implement this method, a numerical model of the engine radiator and power battery waste heat is first established, and the temperature rise characteristics and temperature distribution of the waste heat system are simulated and analyzed. This analysis reveals the heat transfer law of the engine radiator and power battery waste heat. An automatic bidirectional thermal control device based on waste heat reuse is designed. The device utilizes a multi-stage series thermal energy transfer system with phase change materials (PCM) as the medium. A low-temperature experiment is conducted to assess the integration of heating and cooling between the engine and power battery. The results indicate that this method effectively utilizes the engine’s waste heat for both heating and cooling purposes. Specifically, a heat exchanger is used to preheat the power battery using the engine’s cooling residual heat, maintaining the internal battery temperature at 30 °C. Simultaneously, the residual heat from the power battery’s cooling system is circulated back to the engine body, preheating the engine coolant to 42 °C. Compared with existing HEVs, it can save more than 90% of the preheating energy consumption of the engine and power battery. This method can reduce power battery and engine warm-up time by more than 50%, while reducing emissions by more than 40% during engine cold start. This approach effectively addresses the challenge of low-temperature preheating for both power batteries and engines by utilizing cooling residual heat bidirectionally, thereby maximizing energy utilization efficiency in HEV systems and optimizing both battery and engine performance.

Non-repeatability of the WLTP vehicle test results

The paper presents results of considerations on the repeatability of the passenger car test results obtained in the WLTP procedure on a chassis dynamometer. The research concerned the aspects of exhaust emissions and fuel consumption. Measurements were carried out in the WLTC test with a cold engine start and then in four WLTC (Worldwide harmonized Light vehicles Test Cycle) tests with a hot engine start. The following values were measured: average specific distance emissions of hydrocarbons, non-methane hydrocarbons, carbon monoxide, nitrogen oxides, particulate matter and carbon dioxide, specific distance particulate number, and operational fuel consumption. Thus, it was possible to assess the impact of the engine's thermal state at start-up on the test results and the nature of test results repeatability with the start-up of a hot engine. The repeatability of the test results was assessed based on the coefficient of variation obtained in the individual tests and the relationship of the maximum difference between measurement results values in the individual tests for a hot engine start. The obtained test results turned out to be very diverse for the considered parameters and indicated low repeatability. Values of carbon dioxide emissions and operational fuel consumption were definitely the least varied in individual hot engine start tests. The exhaust emission of particulate matter varied the most in individual test iterations. However, the specific distance particulate number was relatively similar between individual tests, less so than the exhaust emission of other pollutants. In the case of different engine thermal state at start-up, the emitted particulate number varied the most in the test results, while the emission of carbon dioxide and operational fuel consumption varied the least. The repeatability of executing the velocity process in WLTC tests at hot engine and cold engine start-up was also examined as processes determining exhaust emissions and fuel consumption. These tests were much more repeatable than the exhaust emission and fuel consumption.

Dynamic Characteristics of the Droplet Impact on the Ultracold Surface under the Engine Cold Start Conditions

Dynamic Characteristics of the Droplet Impact on the Ultracold Surface under the Engine Cold Start Conditions

Effect analysis on hydrocarbon adsorption enhancement of different zeolites in cold start of gasoline engine based on Monte Carlo method

50%–80% of the hydrocarbons in gasoline engine emissions come from during cold starts. Zeolites are often used to adsorb HCs during gasoline engine cold-starting. In order to investigate the effect of adsorption enhancement of different molecular sieves on HCs during gasoline engine cold-starting. In this paper, the adsorption properties of Beta, MOR and FER zeolites at different temperatures were simulated based on Monte Carlo method using propylene and toluene as probe molecules. The results show that all three molecular sieves exhibit good adsorption properties at low temperatures. The adsorption capacity decreased with increasing temperature. The molecular sieves tend to adsorb molecules with diameters similar to the pore size of zeolite. In addition, the three-dimensional zeolites Beta and FER showed better adsorption properties than the one-dimensional zeolites. Based on Monte Carlo method, the adsorption properties of Beta, MOR and FER molecular sieves were investigated at different temperatures under multi-components using toluene, isopentane, propylene, ethylene, methane and water as adsorbents. The results showed that there was a competitive adsorption among the components due to the limited adsorption sites in the molecular sieve channels. Large molecules such as toluene and isopentane occupied most of the adsorption sites and hindered the adsorption of small molecules.

Experimental investigation of atomization characteristics at low temperature environments during diesel engine cold start

Exploring the atomization characteristics of fuel in low-temperature environments is crucial for improving the cold start performance of diesel engines. In this work, based on LIEF-PIV laser testing technology, a diesel engine cold start fuel atomization experimental system was built, which could simulate the internal environment of a diesel engine's cylinder during cold start. The concentration and velocity distributions of free-jet spray and wall-impinging spray at low temperature were measured experimentally. The results showed that the decrease in ambient temperature had a significant impact on the rate of evaporation of fuel droplets, which was mainly reflected in two aspects: the total evaporation of the fuel and the uniformity of the distribution of vapor phase. The decrease in fuel temperature led to a decrease in the conversion efficiency of vapor/liquid phases of the fuel. When the fuel temperature was −20 °C, the distribution range of vapor equivalence ratio near the wall area was 0.11–0.59, which is significantly lower than the other two conditions. In addition, the increase in environmental pressure resulted in a certain decrease in the maximum flow velocity and turbulent flow energy of the mixture, with an average decrease of 0.32 m/s in the maximum flow velocity at the three fuel temperatures of 0 °C, −20 °C, and −40 °C.

Effect of injection pressure on low-temperature fuel atomization characteristics of diesel engines under cold start conditions

Exploring the atomization characteristics and spray impingement characteristics of low-temperature fuel under different injection pressures has important practical significance for improving the cold start performance of diesel engines. In this study, based on LIEF-PIV combined laser testing technology, a fuel atomization experimental system for diesel engine cold start was established. The concentration and velocity fields of low-temperature fuel with the temperature from 20 to - 40 ℃ were experimentally analyzed within the injection pressures of 40-80MPa. The results showed that the increase of injection pressure increased the initial kinetic energy of the diesel droplets, whereas the concentration gradient of spray decreased significantly. Meanwhile, the mixing effect of spray and ambient gas increased. When the fuel temperature decreased from 0 ℃ to - 20 ℃, the values of the average equivalence ratio in the near-wall region decreased from 0.52 to 0.21. The change of injection pressure had an obvious effect on the macro morphology of wall-impinging spray and the flow characteristics of the fuel/air mixture. When the injection pressure increased from 40MPa to 80MPa, the difference of maximum turbulent kinetic energy among various temperatures increased from 0.66 m2/s2 to 0.90 m2/s2.

Co3O4 as an efficient passive NOx adsorber for emission control during cold-start of diesel engines

The Co3O4 nanoparticles, dominated by a catalytically active (110) lattice plane, were synthesized as a low-temperature NOx adsorbent to control the cold start emissions from vehicles. These nanoparticles boast a substantial quantity of active chemisorbed oxygen and lattice oxygen, which exhibited a NOx uptake capacity commensurate with Pd/SSZ-13 at 100 °C. The primary NOx release temperature falls within a temperature range of 200-350 °C, making it perfectly suitable for diesel engines. The characterization results demonstrate that chemisorbed oxygen facilitate nitro/nitrites intermediates formation, contributing to the NOx storage at 100 °C, while the nitrites begin to decompose within the 150-200 ºC range. Fortunately, lattice oxygen likely becomes involved in the activation of nitrites into more stable nitrate within this particular temperature range. The concurrent processes of nitrites decomposition and its conversion to nitrates results in a minimal NOx release between the temperatures of 150–200 °C. The nitrate formed via lattice oxygen mainly induces the NOx to be released as NO2 within a temperature range of 200–350 °C, which is advantageous in enhancing the NOx activity of downstream NH3-SCR catalysts, by boosting the fast SCR reaction pathway. Thanks to its low cost, considerable NOx absorption capacity, and optimal release temperature, Co3O4 demonstrates potential as an effective material for PNA applications.

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.

Research on the results of the WLTP procedure for a passenger vehicle

The article considers variables registered in the WLTP procedure. The test results of a passenger car with a compression-ignition engine have been analysed. The tests were carried out on a chassis dynamometer. The tests were performed for engine cold start and ran up to the point of reaching stabilized operating conditions. The average specific distance emissions and volumetric fuel consumption were assessed for individual test phases as well as for the entire test. It was found that the results in the first test phase, which corresponded to the engine cold start up to stabilized operating conditions, had the most significant impact on the overall exhaust emission and fuel consumption results in the test. The specific distance emissions of carbon monoxide, non-methane hydrocarbons and nitrogen oxides were by far the highest in the first phase of the test. In the fourth phase of the test, the specific distance emissions of methane and carbon dioxide turned out to be the highest, as well as the operational volumetric fuel consumption being the highest.

Energy-based cold-start strategies for diesel engines at extreme low temperature

The cold start of diesel engines at extreme low temperatures is currently one of the most critical problems in the field of transportation. An experiment on the cold start was conducted in a controlled environment, and a one-dimensional simulation model was built to study diesel engine cold start performance based on energy analysis. The cyclic energy loss of cold start failure and success cases, ramp-up-speed period characteristic of diesel engine were studied by using special low temperature diesel and adopting two pilots and one main injection control strategy at −43 ℃. The numerical calculation and analysis results show that when the exhaust energy is high and the heat transfer loss energy is very low, there may be a misfire cycle in the cylinder. The increase in the pilot injection 1 mass, main injection mass, pilot injection 1 timing, and main injection timing within certain limits can significantly increase the fuel vapor fraction during the ramp-up-speed period (maximum of 66.67%). The speed of ramp-up-speed period and idle steady phase faster obviously, the maximum increase is 300 r/min (30%). The fuel vapor fraction increases as the pilot injection 2 mass increases during the ramp-up-speed period but slows down the speed of ramp-up and idle phase, with a maximum decrease of 300 r/min (23.07%).

Experimental study on improving cold start performance of diesel engines at extremely low ambient temperatures with diethyl ether

How to achieve a fast and reliable cold start of diesel engines at extremely low temperatures is a significant and longstanding problem. In this study, a precise amount of diethyl ether was premixed in the intake to facilitate the starting at extremely low ambient temperatures down to −40 °C. The study investigated the effects of diesel fuel injection strategies, diethyl ether concentration, and ambient temperature on the cold-start performance. Additionally, an analysis was conducted on energy consumption and heat loss during the cold start period. The test engine could start quickly and steadily when diethyl ether was premixed in the intake. This was achieved by optimizing the diesel injection quantity to 60% of the original quantity and retarding the injection timing from 6 oCA BTDC to 2 oCA BTDC. The engine exhibited reliable starting at −40 °C when 2.0% v/v diethyl ether was premixed. However, excessive direct injection of diesel had an adverse effect on fuel ignition at such extremely low temperatures. Moreover, the electricity consumption was much lower with diethyl ether premixed in the intake than that with an electric intake heater, greatly reducing the requirements for starting batteries during the cold start under extremely low-temperature conditions.

Hazardous particles during diesel engine cold-start and warm-up: Characterisation of particulate mass and number under the impact of biofuel and lubricating oil

The increasing share of using biofuels in vehicles (mandated by current regulations) leads to a reduction in particle size, resulting in increased particle toxicity. However, existing regulations disregarded small particles (sub-23 nm) that are more toxic. This impact is more significant during vehicle cold-start operation, which is an inevitable frequent daily driving norm where after-treatment systems prove ineffective. This study investigates the impact of biofuel and lubricating oil (as a source of nanoparticles) on the concentration, size distribution, median diameter of PN and PM, and their proportion at size ranges within accumulation and nucleation modes during four phases of cold-start and warm-up engine operation (diesel-trucks/busses application). The fuels used were 10% and 15% biofuel and with the addition of 5% lubricating oil to the fuel. Results show that as the engine warms up, PN for all the fuels increases and the size of particles decreases. PN concentration with a fully warmed-up engine was up to 132% higher than the cold-start. Sub-23 nm particles accounted for a significant proportion of PN (9%) but a smaller proportion of PM (0.1%). The fuel blend with 5% lubricating oil showed a significant increase in PN concentration and a decrease in particle size during cold-start.

Investigation of the injection pressure impact on non-monotonic two-stage ignition delay of diesel engines under cold-start

Poor startability under cold-start conditions is a long-term obstacle of the compression ignition engine and adjustment of the injection pressure is an effective way to improve the startability. Therefore, a detailed investigation of the effect of injection pressure (Pi) on the ignition characteristics of the fuel spray under cold-start conditions is needed. Though numerous studies have been conducted on the effect of Pi on the ignition characteristics of the fuel spray, the two-stage ignition process of the fuel spray under cold-start conditions is still an unknown field. In this paper, the effect of Pi on the two-stage ignition process of the fuel spray under cold-start conditions is investigated in a constant volume combustion chamber through simultaneous Shadowgraphy and high-speed natural luminosity method an analytical model for two-stage ignition delay is established accordingly for further investigation. Based on the experiment results, a monotonic decreasing trend on low-temperature ignition delay time LTI (i.e., form 4.5 ms to 2.5 ms under the ambient temperature of 760 K) and an increasing trend on the cool flame propagation time τ (i.e., form 0.4 ms to 1.6 ms under the ambient temperature of 760 K) are found and finally results in a non-monotonic trend of high-temperature ignition delay (HTI) as the injection pressure raises from 40 MPa to 160 MPa. According to the established model, increased Pi leads to promoted atomization and intensified dilution effect of the fuel spray, which is concluded as the reason for decreased LTI and increased τ, respectively. In this way, the non-monotonic trend of HTI under engine cold-start as Pi increases is quantitatively explained through the promoted model.

Enhanced Exhaust after-Treatment Warmup in a Heavy-Duty Diesel Engine System via Miller Cycle and Delayed Exhaust Valve Opening

The exhaust after-treatment (EAT) threshold temperature is a significant concern for highway vehicles to meet the strict emission norms. Particularly at cold engine start and low loads, EAT needs to be improved above 250 °C to reduce the tailpipe emission rates. Conventional strategies such as electrical heating, exhaust throttling, or late fuel injection mostly need a high fuel penalty for fast EAT warmup. The objective of this work is to demonstrate using a numerical model that a combination of the Miller cycle and delayed exhaust valve opening (DEVO) can improve the tradeoff between EAT warmup and fuel consumption penalty. A relatively low-load working condition (1200 RPM speed and 2.5 bar BMEP) is maintained in the diesel engine model. The Miller cycle via retarded intake valve closure (RIVC) is noticeably effective in increasing exhaust temperature (as high as 55 °C). However, it also dramatically reduces the exhaust flow rate (over 30%) and, thus, is ineffective for rapid EAT warmup. DEVO has the potential to enhance EAT warmup via increased exhaust temperature and increased exhaust flow rate. However, it considerably decreases the brake thermal efficiency (BTE)—by up to 5%—due to high pumping loss in the system. The RIVC + DEVO combined technique can elevate the exhaust temperature above 250 °C with improved fuel consumption—up to 10%—compared to DEVO alone as it requires a relatively lower rise in pumping loss. The combined method is also superior to RIVC alone. Unlike RIVC alone, the RIVC + DEVO combined mode does not need the extreme use of RIVC to increase engine-out temperature above 250 °C and, thus, provides relatively higher heat transfer rates (up to 103%) to the EAT system through a higher exhaust flow rate. The RIVC + DEVO combined method can be technically more difficult to implement compared to other methods. However, it has the potential to maintain accelerated EAT warmup with improved BTE and, thus, can keep emission rates at low levels during cold start and low loads.

Real-Time Simulation of CNG Engine and After-Treatment System Cold Start Part 1: Transient Engine-Out Emission Prediction Using a Stochastic Reactor Model

<div class="section abstract"><div class="htmlview paragraph">During cold start of natural gas engines, increased methane and formaldehyde emissions can be released due to flame quenching on cold cylinder walls, misfiring and the catalyst not being fully active at low temperatures. Euro 6 legislation does not regulate methane and formaldehyde emissions. New limits for these two pollutants have been proposed by CLOVE consortium for Euro 7 scenarios. These proposals indicate tougher requirements for aftertreatment systems of natural gas engines.</div><div class="htmlview paragraph">In the present study, a zero-dimensional model for real-time engine-out emission prediction for transient engine cold start is presented. The model incorporates the stochastic reactor model for spark ignition engines and tabulated chemistry. The tabulated chemistry approach allows to account for the physical and chemical properties of natural gas fuels in detail by using a-priori generated laminar flame speed and combustion chemistry look-up tables. The turbulence-chemistry interaction within the combustion chamber is predicted using a K-k turbulence model. The optimum turbulence model parameters are trained by matching the experimental cylinder pressure and engine-out emissions of nine steady-state operating points.</div><div class="htmlview paragraph">Subsequently, the trained engine model is applied for predicting engine-out emissions of a WLTP passenger car engine cold start. The predicted engine-out emissions comprise nitrogen oxide, carbon monoxide, carbon dioxide, unburnt methane, formaldehyde, and hydrogen. The simulation results are validated by comparing to transient engine measurements at different ambient temperatures (-7°C, 0°C, 8°C and 20°C). Additionally, the sensitivity of engine-out emissions towards air-fuel-ratio (λ=1.0 and λ=1.3) and natural gas quality (H-Gas and L-Gas) is investigated.</div></div>

Influence of the In-Cylinder Catalyst on the Aftertreatment Efficiency of a Diesel Engine

The article discusses the use of a catalyst inside the cylinder, the task of which is to reduce exhaust emissions from a diesel engine. The catalyst (platinum) applied to the glow plugs provided an additional method of exhaust aftertreatment. Due to their usage, especially in urban driving, passenger cars are characterized by small mileage between individual trips, so they often operate from a cold engine start and work at a low engine temperature, which leads to reduced catalytic reactor efficiency. For this reason, the efficiency of the internal catalyst was tested in relation to the efficiency of the external reactor. This efficiency was determined based on exhaust emission measurements (before and after the catalytic reactor) in two stages: stage 1: idling of a hot engine, and stage 2: simulation of the NEDC test (valid for the selected test object). The tests were carried out on an engine dynamometer, where the traffic conditions from the type-approval test carried out on a chassis dynamometer could be replicated. The tests were carried out on a Euro 4 1.3 JTD MultiJet diesel engine. The results (measurement of carbon monoxide, hydrocarbons, and the number of particles) related to the assessment of the effect the catalyst in the cylinder were discussed. The obtained catalytic reactor efficiency results, regardless of the type of research, indicated that it achieved the highest efficiency in reducing the concentration of hydrocarbons, and the lowest—in relation to the number of solid particles (as that is not its primary function). It is particularly significant that the in-cylinder catalytic converter was most efficient during the cold engine start, which happens frequently in urban driving. The efficiency of the diesel oxidation catalytic reactor (DOC) during the engine start-up and warm-up phases with the use of standard glow plugs reached values of 31.3%, 34.1% and 14.3%, respectively, for carbon monoxide, hydrocarbons and the particle number. On the other hand, the determined efficiency of the DOC in a setup with the modified glow plugs was 28.9%, 35.7% and 12.5%, respectively. The proposed solution can be used to improve the combustion quality in internal combustion engines used in hybrid vehicles, which are characterized by frequent engine starts and stops. In addition, it is possible to use such a solution retroactively in traditional vehicles powered by an internal combustion engine, which could result in an improvement in their emission class through what is called retrofitting.

Effect analysis on hydrocarbon adsorption enhancement of ZSM-5 zeolite modified by transition metal ions in cold start of gasoline engine

The adsorption effects of transition metal modified ZSM-5 zeolite on the main hydrocarbon emission components of gasoline engine cold start include acetylene (C2H2), ethylene (C2H4), acetaldehyde (C2H4O), propylene (C3H6), 1-butene (C4H8) and benzene (C6H6) carbon monoxide (CO), carbon dioxide (CO2) and water vapor (H2O) were studied by experiments and molecular simulation. Through the hydrocarbon adsorption breakthrough experiment, the promotion effect of Fe-ZSM-5 zeolite on the adsorption of hydrocarbon emissions from cold start was confirmed. Results showed that the Fe modification improved the adsorption rate of zeolite on C4H8 and C2H4O. With the increase of Fe mass fraction, the adsorption capacity of zeolite for C2H4O increased, while the adsorption capacity for C4H8 decreased. The adsorption mechanisms of 9 main exhaust components from cold start on M2+ (M = Fe, Cu and Zn) modified ZSM-5 zeolite were studied by molecular simulation. Under the cold start condition, the adsorption capacity of H2O is the largest, between 1.5 and 4 mmol/gzeo, one order of magnitude higher than that of CO2 (0–0.3 mmol/gzeo), C6H6 (0–0.16 mmol/gzeo), C2H4O (0–0.5 mmol/gzeo) and C4H8 (0–1.6 mmol/gzeo), and 3–4 orders of magnitude higher than that of CO, C2H2, C2H4, C3H6. Results showed that the adsorption priority of molecules on transition metal ion modified ZSM-5 zeolite was determined by functional group charge number, molecular weight and molecular polarity. The zeolite with higher ion exchange ratio has a larger adsorption capacity for oxygen-containing molecules such as H2O, CO2 and C2H4O. Reducing the ion exchange ratio was conducive to the adsorption of hydrocarbons such as C4H8.

Impact of the Internal Combustion Engine Thermal State during Start-Up on the Exhaust Emissions in the Homologation Test

Due to the increasingly restrictive exhaust emissions requirements from conventional vehicles, the internal combustion engine start-up seems to be most important part of engine operation. The period immediately after starting the engine is the time when the exhaust emissions are highest, thus, this aspect is currently subject to heavy analysis. The article evaluates the impact of the engine thermal state during its start-up for a Euro 5 emission class vehicle type approval test. The engine thermal state during start-up turned out to have a crucial influence (throughout the approval test) on the results of the hydrocarbons road emission (a difference of about 1500%) and the road emission of carbon monoxide (63%). The remaining road exhaust emission values were less sensitive to the thermal state of the engine during start-up—the nitrogen oxides emission value increased by 18% (for a cold start compared to a hot start), and the road fuel consumption (and thus the emission of carbon dioxide) increased by about 6%. In conclusion, the authors refer to technical solutions that may have a significant impact on reducing the exhaust emissions in the considered period of engine cold start.

Enhanced CO resistance of Pd/SSZ-13 for passive NOx adsorption

Passive NOx adsorption (PNA) is a novel technology to control NOx emissions during cold start. However, the recent generation of PNA material, Pd/zeolite, suffers from major degradation under high CO concentrations. In this work, we developed a novel form of Pd/SSZ-13 by using a freeze-drying process after incipient wetness impregnation. This Pd/SSZ-13 showed a better stability than the sample synthesized by the common process. Several characterization measurements were conducted and it was found that the Pd sites on the freeze-dried sample were more resistant towards CO-induced agglomeration. By combing in-situ characterization and kinetic modeling, we found that the freeze-dried Pd/SSZ-13 had more ion-exchanged Pd sites, which provided greater resistance towards the CO-induced Ostwald ripening process, and consequently suppressed the sintering behavior under a high CO concentration. This material offers a potentially improved stability of PNAs under extremely high CO concentration pulses from incomplete diesel combustion during engine cold start.