Cold Start Conditions Research Articles

The effect of after-treatment techniques on the correlations between driving behaviours and NO emissions of passenger cars

Nitrogen oxides (NO x ) emissions from passenger cars are significantly dependent on after-treatment techniques, cold start conditions, and driving behaviours. The widely-used selective catalytic reduction (SCR) technique has low effectiveness of reducing NO x emissions during the cold start period or at low speeds. As a new technique, ammonia creation and conversion technology (ACCT) system can further decrease NO x emissions to achieve cleaner travelling. The correlations between driving behaviours and NO x emissions are different for vehicles equipped with SCR and ACCT systems over cold start and warm start driving cycles. In this paper, the effect of SCR and ACCT systems on the correlations between driving behaviours and NO x emissions were explored based on worldwide harmonized light vehicle test cycles (WLTC). The results indicated that vehicle fuel consumption rates almost linearly increased with acceleration when the acceleration was higher than −0.5 m/s 2 . For cold start situations, vehicle speed range of 55 km/h∼ 100 km/h presented the lowest NO x emission factors over SCR and ACCT scenarios. SCR efficiency was lower than 60% for the vehicle speed range of 25 km/h∼ 40 km/h, and the efficiency of ACCT system was higher than 65% in the corresponding speed range. Regarding the warm start scenarios, average catalyst efficiency was higher than 80% for SCR system over the speed range of 25 km/h∼ 40 km/h, and ACCT efficiency was higher than 95% for all the speed and acceleration ranges. Applications of ACCT systems provided a possibility of meeting stricter emission regulations, and the relationships between driving behaviours and NO x emissions provided the guidance for eco-driving to achieve cleaner travelling. • Effect of NO x reduction techniques on correlations of NO x and driving behaviours. • Catalyst efficiency was <50% for part of medium-low engine speed after warm up. • SCR efficiency was <60% in the speed range of 30 km/h∼ 40 km/h over cold start case. • Speed range of 30–60 km/h dominated total pipe-out NO x emissions for all the cases. • Pipe-out NO x emission factors were less depended on vehicle acceleration than speed.

A numerical investigation of injection pressure effects on wall-impinging ignition at low-temperatures for heavy-duty diesel engine

The effect of injection pressure on impinging ignition at low temperatures is not systematic or even confusing. This work is to reveal the impinging ignition mechanism by the numerical method to further improve the success rate and thermal efficiency at cold-start conditions in a diesel engine. In which, n-dodecane was used as the diesel surrogate, and the intermediate reaction radicals, equivalence ratio, and temperature were studied to analyze chemical reaction processes and local burn conditions. The simulation well represents the experiments. The results show that increasing injection pressure with the same mass leads to a faster fuel spreading and makes the mixture region wider and leaner for the impinging spray simulations, and the spray-wall impingement can instantly change the direction of the fuel movement and make fuel more dispersed. Under low-temperature cold-wall conditions, the physical ignition conditions are gradually destroyed due to the diffusion during longer ignition delay and finally result in misfire at higher injection pressure. In the misfire case, there is a generation of CH2O, but no obvious generation of OH. It proves that the low-temperature reactions occurred but transition into high-temperature reaction was stopped even the local temperature has reached the decomposition threshold (1000 K) of H2O2. However, lengthening injection duration can guarantee the success of ignition at higher injection pressures. It indicates that concentration is a key parameter for triggering the high-temperature reaction, and which can be made up by extending the injection duration. This research proves and explains why the lower injection pressure is helpful to the combustion in the cold start process from the mechanism level, and also has important implications for the design of fuel injection strategy in diesel engine cold start.

Improving computational fluid dynamics modeling of Direct Injection Spark Ignition cold-start

Developing a profound understanding of the combustion characteristics of the cold-start phase of a Direct Injection Spark Ignition (DISI) engine is critical to meeting increasingly stringent emissions regulations. Computational Fluid Dynamics (CFD) modeling of gasoline DISI combustion under normal operating conditions has been discussed in detail using both the detailed chemistry approach and flamelet models (e.g. the G-Equation). However, there has been little discussion regarding the capability of the existing models to capture DISI combustion under cold-start conditions. Accurate predictions of cold-start behavior involves the efficient use of multiple models - spray modeling to capture the split injection strategies, models to capture the wall-film interactions, ignition modeling to capture the effects of retarded spark timings, combustion modeling to accurately capture the flame front propagation, and turbulence modeling to capture the effects of decaying turbulent kinetic energy. The retarded spark timing helps to generate high heat flux in the exhaust for the faster catalyst light-off during cold-start. However, the adverse effect is a reduced turbulent flame speed due to decaying turbulent kinetic energy. Accordingly, developing an understanding of the turbulence-chemistry interactions is imperative for accurate modeling of combustion under cold-start conditions. In the present work, combustion characteristics during the cold-start, fast-idle phase is modeled using the G-Equation flamelet model and the RANS turbulence model. The challenges associated with capturing the turbulent-chemistry interactions are explained by tracking the flame front travel along the Borghi-Peters regime diagram. In this study, a modified version of the G-Equation combustion model for capturing cold-start flame travel is presented.

Influence of flash boiling and swirl ratio on the gasoline spray structure in a spark-ignition optical engine: An experimental study

Cycle-to-cycle variation (CCV) of engine output not only results in fluctuations of the engine torque, but also prohibits the engine from operating at its optimal design condition. Considering that it is difficult to control the sources of variation, designing a combustion system that is more robust to the root causes of variation is therefore a more viable option. This paper assesses the influence of flash boiling and swirl ratio on the characteristics and CCV of spray structure in an optical single-cylinder spark-ignition direct-injection (SIDI) engine. The experiment was carried out under cold-start condition. The spray conditions studied include liquid, transitional flash boiling and flare flash boiling. Crank angle resolved spray images were recorded in a tumble plane for 50 consecutive cycles using high-speed laser scattering technique. Results show that the flash boiling spray is strongly influenced by air flow with the penetration decreasing and the spray angle increasing with swirl ratio. Also the penetration of flash boiling spray is shorter than that of the liquid spray, which is beneficial to reduce impingement with piston. Results also show that high swirl increases the CCV of spray, but flash boiling helps to mitigate the cyclic variation induced by high swirl.

Wear resistance mechanism of engine piston skirt coating under cold start condition

At the beginning of cold start, the lubricating oil temperature is low, the kinematic viscosity is high, the splash lubrication effect is poor, and the good lubricating oil film cannot be formed, therefore, the friction and wear between piston and cylinder is serious. In this paper, the wear mechanism of aluminum alloy piston skirt coating was studied in the cold start stage with severe wear degree: the dynamic simulation and cold start test analysis were carried out for the skirt with or without coating, and the wear morphology, knife pattern structure and friction force were compared, so as to determine the friction reduction energy efficiency of the coating in the cold start stage.

Study of flash boiling combustion with different fuel injection timings in an optical engine using digital image processing diagnostics

Flash boiling atomization is considered a potential solution to multiple issues encountered in fuel atomization for internal combustion engine applications. It has been demonstrated that flash boiling combustion can reduce soot emission under cold-start conditions, while the analysis was still preliminary and limited to engine cold-start conditions. This work investigates the performance of flash boiling combustion in comparison to sub-cooled spray combustions realized with the variation of injection timing. An optical engine facility was used to capture the combustion characteristics with a high-speed color camera, with the temperature of the engine coolant maintained at 60 °C. HSV color model and modified digital CH*/C2* ratio (excess air intensity) to study different flame regions and local combustion richness in the optical engine. The results show that under the conditions tested, flash boiling can improve the efficiency of the engine while reducing the PN emission simultaneously. Furthermore, it was seen that flash boiling combustion could yield a faster flame speed, uniform distribution of flames and less rich mixtures. Finally, color model analysis for transient and averaged flame images is also in good agreement with actual engine performance.

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.

Extended Model for Filtration in Gasoline Particulate Filters under Practical Driving Conditions.

In order to reliably predict the particle number filtration of gasoline particulate filters (GPF) under practical driving conditions, an extension to established filtration models is developed. For the validation of this approach and in order to close a gap of available measurement data at high space velocity in the literature, the particle-size-resolved fresh filtration efficiency of seven different cordierite filters is determined experimentally. Moreover, the experiments on a dynamic engine test bench focus on the impact of the pore-size distribution and the filter wall thickness under steady-state as well as transient, cold-start conditions. In order to model all trends observed, a new correlation for the particle collection due to inertial deposition is proposed and embedded in a heterogeneous multiscale model framework for a GPF. The presented approach can predict all trends observed in the measurements, including a stabilization of the filtration efficiency with increasing space velocities above a certain level. A comparison of several modeling approaches reveals the partly different behaviors at varying space velocities for the here presented model as well as for established filtration models.

Water management characteristics of electrospun micro-porous layer in PEMFC under normal temperature and cold start conditions

Micro-porous layer (MPL) is the key component in proton exchange membrane fuel cell for water management. Electrospinning technique, providing a novel nanofiber structure, is recently used to fabricate MPL which gave improved fuel cell performance at normal temperature operation. However, underlying causes are not well understood, and no attempt has been made to study its effects on the cold start performance. In this work, electrospun MPL using non-toxic solvent was fabricated, and water management characteristics under both normal temperature and cold start conditions were compared with commercial MPL using the same catalyst coated membrane (CCM). Electrospun MPL outperformed the commercial MPL at 70 °C under high relative humilities due to marked reduction in mass transport losses. Under cold start conditions, fuel cell with electrospun MPL generated electricity for a longer time, possibly due to better interfacial connection, which facilitated water removal from catalyst layer.

Biodiesel Blends Startability and Emissions During Cold, Warm and Hot Conditions

The time and emissions during cold starting were investigated at cold and hot temperatures (i. e., – 10°C, 0 °C, 25°C and 50 °C). The effect of injection timing (IT) on these factors was also studied at four ITs before top dead centre (BTDC) i. e., (12 , 15 , 20 and 23 BTDC). The results were compared with engine operation at 17 BTDC (factory IT). Sunflower vegetable oil and yellow grease were used as raw materials to prepare bio diesel fuels through transesterification. B20 (20% sunflower oil biodiesel+80% diesel) and W20 (20% yellow grease biodiesel+80% diesel), together with neat conventional Iraqi diesel fuel, were used to analyse engine startability and emissions under cold and hot starting conditions. Results indicated that adding biofuel affects the engine starting response and that the starting time stabilises at high starting temperatures. At a low starting temperature (i. e.,–10 °C), hydrocarbon (HC) and carbon monoxide (CO) concentrations increase significantly. At moderate and high starting temperatures, the oxygen content in the biofuel blend plays a dominant role in reducing the HC and CO concentrations. Smoke opacity has increased notably for the biodiesel blends at low starting temperatures but has decreased significantly at moderate and high starting temperatures. Both biofuel blends emit higher levels of nitrogen oxide than the neat diesel fuel. Noise increases at low starting temperatures, thereby indicating rough combustion.

Visualization Research on Low-Temperature Ignition and Combustion Characteristics of Diesel/Gasoline Blends Under Cold-Start Conditions

Abstract Although engines fueled with diesel/gasoline blends show excellent combustion and emission performance, its low-temperature flame development characteristics under cold-start conditions remain to be further verified. To clarify the details, experiments were conducted in an optical constant volume combustion chamber using Mie-scattering and direct photography methods at different ambient temperatures. Results show that the ignition delay of pure diesel during spray combustion shows a zero temperature coefficient (ZTC) region, and the addition of gasoline weakens the ZTC behavior until it disappears. The cool flame initiates the ignition, and the hot flame tends to far from the base of the cool flame as the gasoline content increases. In addition, the addition of gasoline to diesel increases the ratio of cool flames because the high evaporation reduces the temperature in the mixing zone, so only cool flame occurs in the G45 blends. Consequently, the total flame intensity presents an order of magnitude decrease. At lower ambient temperatures, the addition of gasoline significantly increases ignition instability. It is difficult to convert a cool flame into a hot flame due to the inhomogeneity of temperature and species field, which results in various unstable ignition phenomena, such as a short flash cool flame and intermittent cool and hot flame. Therefore, it is essential to directly target the cool flame and pay attention to the intrinsic mechanism of the evolution from the cool flame to the hot flame during the spray combustion process.

A comparative experimental study on emission characteristics of a turbocharged gasoline direct-injection (TGDI) engine fuelled with gasoline/ethanol blends under transient cold-start and steady-state conditions

In this study, the emissions of a TGDI engine were experimentally investigated and compared under transient cold-start operating and steady-state operating conditions, respectively. Furthermore, the steady-state emissions of the TGDI engine under different coolant out temperature (43 °C, 65 °C, 88 °C, 102 °C and 110 °C) were compared to the transient emissions. The results indicated that the transient NOx emissions and the steady-state NOx emissions were strongly depended on the load of the TGDI engine. Moreover, under steady-state operating conditions, the NOx emissions of the TGDI engine were increased with the coolant temperature from 43 °C to 102 °C, while the NOx emissions were decreased at the outlet coolant temperature of 110 °C due to retard the spark timing. Apart from that, the HC emissions under transient cold-start condition were approximately ten times than that of the steady-state conditions. Under steady-state operating conditions, the HC emissions were basically decreased with the coolant temperature from 43 °C to 110 °C due to reduction of the flame quenching distance. The excess air ratio of the TGDI engine slightly fluctuated around stoichiometric air/fuel ratio under the NEDC, while the excess air ratio was literally off the charts during the deceleration operating conditions due to the fuel cut-off. CO emission periodically reached a peak value at deceleration operating conditions under transient cold start condition, while CO emission was much high at the high-load and high-speed regions under steady-state operating conditions. In addition, the outlet coolant temperature did not present an obvious effect on the CO emission formation.

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.

Robust Hybrid Cooperative Positioning Via a Modified Distributed Projection-Based Method

Cooperative positioning is attracting an increasing amount of attention due to its ability to enhance the accuracy and availability of positioning performance. Current algorithms for cooperative positioning are sensitive to the initial guess as a result of their nonconvex objective functions, which is especially true in hybrid wireless networks. Perfect a priori information about the locations is needed, which is rather problematic in many scenarios. With strong convergence, the iterative parallel projection method (IPPM) is extended to hybrid wireless networks (H-IPPM) in this paper. Motivated by the fact that normal weighted methods cannot achieve the optimal solution, the position uncertainty is modeled, and two distributed weighted parallel projection algorithms, namely, an inexact weighted algorithm called the HBFW-IPPM and an exact weighted algorithm called the HCPW-IPPM, are developed when considering both the range measurement errors and position uncertainty. Experiments in a realistic outdoor scenario are conducted. The results indicate that the exact weighted algorithm HCPW-IPPM shows superior and robust performance in both warm-start and cold-start conditions, and this is true even when non-line of sight (NLOS) measurements and weight estimation errors are taken into account.

Evaporation of free falling droplets of binary alkane-ethanol blends

The admixture of ethanol to gasoline has become a key factor to reduce the reliance on fossil fuels. In this context, the distinct occurrence of component-by-component evaporation compromises the efficient and the low-emission operation of internal combustion engines due to inhomogeneous mixture formation. In order to meet these challenges, a more precise understanding of the mechanisms causing the component-by-component evaporation is inevitable. Therefore, in the present study the evaporation behaviour of binary alkane-ethanol blends has been experimentally investigated. A high-resolution Raman-setup is combined with a fast trigger system to quantify the substance composition of the gaseous phase directly behind free falling droplets. Considerable preparatory work has been carried out to achieve controlled and consistent measurement conditions and to achieve a quantitative and a substance related evaluation under cold start conditions. Binary blends of ethanol and n-hexane, iso-octane or n-decane are studied. A systematic variation of the droplet temperature, the falling distance, the droplet generating frequency and the relative ratios of the applied substances are accomplished. The evaluation demonstrates partially strong component-by-component evaporation dependent on the measurement conditions. Blends of ethanol and hexane in a mixture of 85/15 vol-% and of ethanol and decane with 10/90 vol-% show a distinct influenceability of the varied conditions. Furthermore, the results indicate a depletion of the more volatile component at the droplet surface. With increasing temperature, the depletion and the component-by-component evaporation are promoted. Finally, a decisive influence of the droplet spacing, the droplet temperature and the falling distance is described.

A Novel Technique for Measuring Cycle-Resolved Cold Start Emissions Applied to a Gasoline Turbocharged Direct Injection Engine

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;There is keen interest in understanding the origins of engine-out unburned hydrocarbons emitted during SI engine cold start. This is especially true for the first few firing cycles, which can contribute disproportionately to the total emissions measured over standard drive cycles such as the US Federal Test Procedure (FTP). This study reports on the development of a novel methodology for capturing and quantifying unburned hydrocarbon emissions (HC), CO, and CO&lt;sub&gt;2&lt;/sub&gt; on a cycle-by-cycle basis during an engine cold start. The method was demonstrated by applying it to a 4 cylinder 2 liter GTDI (Gasoline Turbocharged Direct Injection) engine for cold start conditions at an ambient temperature of 22°C. For this technique, the entirety of the engine exhaust gas was captured for a predetermined number of firing cycles. By capturing the exhaust of different numbers of firing cycles, from one to five for example, the emissions contribution of each successive cycle was determined on an ensemble average basis. The development of custom engine control software allowed predetermined event-by event control of individual cylinder fuel injection and spark settings. A dual injection strategy was studied with both an early and a late injection. Emitted masses of HCs (on a C&lt;sub&gt;3&lt;/sub&gt; propane basis), CO and CO&lt;sub&gt;2&lt;/sub&gt; were measured for each successive cycle. It was found that the first two firing cycle out of five contributed the most unburned hydrocarbon and CO mass, with emissions decreasing for later cycles. Measured cycle-resolved HC mass decreased monotonically from approximately 35 mg for the first firing cycle to less than 5 mg for the 5th cycle, an inordinately high value potentially due to misfires at the first two firing events. Cycle-resolved CO masses were on the order of approximately 15 mg per cycle. An advantage of the technique is that is not subject to some of the possible sampling issues that may be encountered with the use of a modal approach (i.e., fast FID + mass flow estimation) and allows the cycle-resolved quantification of CO and CO&lt;sub&gt;2&lt;/sub&gt; mass quantities in addition to HC mass.&lt;/div&gt;&lt;/div&gt;

Degradation of the Sealing Silicone Rubbers in a Proton Exchange Membrane Fuel Cell at Cold Start Conditions

Degradation of the Sealing Silicone Rubbers in a Proton Exchange Membrane Fuel Cell at Cold Start Conditions

Doping Manganese Oxides with Ceria and Ceria Zirconia Using a One-Pot Sol\u2013Gel Method for Low Temperature Diesel Oxidation Catalysts

Octahedral molecular sieves (OMS-2) are an interesting form of manganese oxide with a 2 × 2 edge sharing tunnel structure and a cation positioned inside. Cryptomelane is an OMS-2 material with K+ cations within the crystalline tunnel and has been widely used in catalytic oxidation reactions, due to a mixed valency of Mn3+ and Mn4+ cations. Cryptomelane (K-OMS-2) can be modified by structural incorporation of various dopants and tunnel cations which can enhance the catalytic activity of the material. It also offers to be a promising alternative material for the low temperature emission control of combustion vehicles; particularly during cold start and low temperature conditions of diesel vehicles. In this work we used a one-pot sol–gel route to synthesize a range of manganese oxide based supports doped with Ce and CeZrO2, as alternative low temperature diesel oxidation catalysts. We have investigated the combination of manganese, ceria and zirconia in mixed oxide catalyst supports. The synthesized samples were loaded with 1 wt% Pt and their activity in the oxidation reactions of CO and C3H6, were compared with a commercial diesel oxidation catalyst with the same metal loading. The reductions in CO and C3H6 oxidation temperature T50 of 109 K and 81 K respectively was achieved compared to a commercial diesel oxidation catalyst.

Experimental and Computational Investigation of Diesel and Gasoline Injection in a Direct Injection Compression Ignition Engine

In this paper, the numerical simulation of the diesel and gasoline fuels injection in a constant volume chamber and in a cylinder under the operating conditions of a compression ignition (CI) engine is conducted. The simulation results are compared with the experimental data which derived from fast imaging techniques. In order to check out the possibility of using gasoline instead of diesel to increase the volumetric efficiency of the CI engine, the spray characteristics of the gasoline and diesel with injection pressures of 40 and 80 MPa, as well as temperatures of 243, 273 and 313 K, under cold start condition is investigated. The results show that under the same conditions, the vapor penetration length for the two fuels is approximately equal and due to the lower volatility of the diesel fuel, its liquid penetration length in 40 and 80 MPa injection pressures was found to be 7 and 9 mm higher than gasoline, respectively. In addition, the reduction in fuel temperature from 313 K to 243 K leads an increase in the penetration of gasoline and diesel liquids by 12 and 10 mm, respectively. Finally, the decrease in the evaporation rate causes a non-homogeneous mixture and results an increase in the unburned hydrocarbons and emissions.

NOx Emissions from Euro 5 and Euro 6 Heavy-Duty Diesel Vehicles under Real Driving Conditions

Despite the strengthening of vehicle emissions standards and test methods, nitrogen oxide (NOx) emissions from on-road mobile sources are not being notably reduced. The introduction of real driving emission (RDE) regulations is expected to reduce the discrepancy between emission regulations and actual air pollution. To analyze the effects of RDE regulations on heavy-duty diesel vehicles, pollutants emitted while driving were measured using a portable emission measurement system (PEMS) for Euro 5 and Euro 6 vehicles, which were produced before and after RDE regulations, respectively. NOx emissions were compared as a function of emissions allowance standards, gross vehicle weight (GVW), average vehicle speed, and ambient temperature. NOx emissions from Euro 6 vehicles were found to be low, regardless of GVW; emissions from both vehicular categories increased with a decline in the average speed. To reflect real road driving characteristics more broadly in the RDE test method for heavy-duty vehicles, it is necessary to consider engine power, which is a criterion for classifying effective sections, in the moving average window (MAW) analysis method, as well as including cold start conditions.