Figure 3 - uploaded by Michael Clairotte
Content may be subject to copyright.
Generic cool-down curve for engine coolant (Source: EC, 2015)

Generic cool-down curve for engine coolant (Source: EC, 2015)

Source publication
Technical Report
Full-text available
The European Union implemented in 2016 the first two packages of the Real-Driving Emissions (RDE) test procedure as Regulations 2016/427 and 2016/646. The third regulatory RDE package addressing cold-start emissions, the testing of hybrid vehicles, and the measurement of particle number emissions was approved by a technical committee of experts fro...

Contexts in source publication

Context 1
... cool-down of engines and after-treatment systems (and their subsequent end-point temperature) generally depends on vehicle-specific design characteristics, on the driving pattern prior to vehicle parking and the ambient temperature. As a first, and relatively conservative proxy, we assume based on own assessments depicted in Figure 3 that after a parking duration of 3-8 h 4 , engine and after-treatment systems have cooled down. Depending on the specific background information available from the various studies, we therefore assume that trips following a parking duration in the range of some 3-8 h contain a cold start. ...
Context 2
... a parking duration shorter that 6 h as criterion to distinguish between trips with and without cold start would increase the percentage of trips containing a cold start. At an ambient temperature of 15 o C, the engine coolant temperature may have approximately reached the ambient temperature (see Figure 3). We acknowledge that the level of pollutant emissions depends on the temperature of the after-treatment systems (but not directly on the temperature of the engine). ...
Context 3
... the parking of a vehicle, the cooling of engine and after-treatment systems typically follows an exponential trend with temperatures decreasing at a declining rate over time, eventually approaching the ambient temperature asymptotically. Figure 3 shows that at an ambient temperature of 15 o C, the engine coolant temperature (a proxy for the temperature of the engine and after-treatment systems) might have fallen to below 30 o C after a parking duration of 3 h 6 , which appears to represent some 30% of all parking events in Modena (De Gennaro et al. (2014); Table 3). Applying the more stringent 3 h criterion to distinguish between trips with and without cold start yields an average distance travelled between two consecutive cold starts of (8 ± 3) km/30% = 27 ± 8 km and a median distance between two consecutive cold starts of 30 km*20%/30% = 20 km. ...
Context 4
... note that the cold-start frequency of 60% as identified by Klein frequency of cold starts is most likely caused by different assumptions regarding the minimum parking time after which the engine has cooled down and a new trip begins with a cold start. According to Table 3, 60% of parking times in Modena (Italy) are within a duration of 0.5 h; this time interval is relatively short to allow for engine cool-down (see also Figure 3). In fact, Klein et al. (2015) do not specify the duration of parking time used to determine whether a vehicle start is a cold start. ...
Context 5
... The choice of a 3-8 h parking duration to differentiate between cold-start and warm- start trips accounts (to some extent) for the cold-start definition in the RDE test procedure. In real-word driving, also substantially shorter parking durations may lead to a cold start, e.g., vehicles are driven over comparatively short trips or if driving and parking occur at lower ambient temperatures that the 15 o C assumed in Figure 3. Additional research considering the actual cool down of after-treatment technologies of a sample of vehicles is necessary to verify our results. ...

Citations

... On the other hand, in urban areas, the act of starting a vehicle from a cold state can make a meaningful contribution to both overall emissions and fuel consumption [11]. This is primarily attributed to the prevalence of short journeys and frequent engine initiations [12]. Dropping the ambient temperature ranging from 77 • F to 46.4 • F within the initial 300-s period led to an increase in CO 2 , a surge in CO, and a decline in NOx [13]. ...
... = a 11 x 1 + a 12 x 2 + ... + a 112 x 12 y 2 = a 21 x 1 + a 22 x 2 + ... + a 212 x12 ... y 12 = a 121 x 12 + a 122 x 12 + ... + a 1212 x 12 ...
Article
Highlights • Collecting data from routes on working days and holidays during peak hours in Shiraz City. • Utilize the Analytic Hierarchy Process (AHP) for selecting test routes. • Using K-means clustering and PCA algorithms to design real driving cycles. • Considering 12 characteristic parameters in generating each drive cycle. • Deriving HC, CO, NOx emissions, and fuel consumption via ADVISOR simulation software. Abstract Understanding the factors affecting internal combustion engine performance is crucial for improving emissions and fuel efficiency in real traffic. This paper investigates the influence of date-specific factors, such as working days and holidays on fuel consumption and emissions of a representative internal combustion engine in the context of Shiraz city. The data was collected by measuring the speed of vehicles on a specific route during peak traffic times on both working days and holidays. The determined route was calculated by a qualitative and quantitative method. K-means clustering and principal component analysis are employed to design representative driving cycles, then combining micro-trips and smoothing them to develop driving cycles. Characteristics of both driving cycles, emissions such as HC, NOx, CO, and fuel consumption were specified under a simulated vehicle model of Peugeot 206 and placed through both real driving cycles by using advanced vehicle simulation software. It has been observed that variations in fuel consumption and emissions between holidays and working days can be attributed to distinct driving patterns and characteristic parameters, such as acceleration, speed, and driving time. Contrary to common assumptions, the study found that fuel consumption was approximately 8 % higher on holidays compared to working days, primarily due to increased driving time and higher average speeds. Moreover, higher acceleration and speed on holidays led to a significant increase in CO emissions (about 36 %) and NOx emissions (about 4 %) compared to working days. However, HC emissions were found to be 27.03 % higher on working days according to lower speed. This study helps in reducing fuel consumption and emissions by uncovering internal combustion engine factors, optimizing driving patterns, and promoting sustainable transport on working days and holidays. Keywords Date-specific; Emissions; Fuel consumption; Real driving cycle; Vehicle simulation
... The area necessary to build a road (30 to 40 m on average) is much larger than the requirements for railway traction (10 to 14 m) [25]. What's more, 30% of car journeys in the European Union do not exceed 3 km, and 50% -6 km [39], so they could be successfully replaced by environmentally friendly natural forms of transport, such as bicycles. ...
Article
Full-text available
Emissions from transport account for 20%–25% of global carbon dioxide emissions, with more than 70% coming from road transport, making it an extremely important topic in the context of decarbonization. The aim of the article is to analyze the trend of CO2 generated from road transport, taking into account the its various sources, and also to examine the manner in which reduced mobility during the pandemic affected the emissions at the time. For this purpose, a time series containing observations up to the pandemic outbreak and a time series containing additional observations from the pandemic period were analyzed. For each time series, a trend was determined and described by a polynomial and then verified to see if the pandemic phenomenon significantly affects a parameter of the proposed model, using appropriate statistical tests.
... When the engine is heated to the state of stabilized operating conditions, its properties are independent of its thermal state. On the other hand, when starting a cold engine, its properties may be strongly dependent on its thermal state-primarily pollutant emissions, fuel consumption, general efficiency, and useful power [16][17][18][19][20][21][22][23][24][25][26][27]. ...
... Consequently, there is a need to feed engines with a richer mixture, and this is the third reason for the deterioration of the performance of internal combustion engines during the warm-up phase. This leads to an increase in fuel consumption and an increase in exhaust emissions, primarily of substances with oxygen-reducing properties-mainly organic compounds and carbon monoxide, as well as particulate matter [16,23,26,27]. The third reason for the engine performance deterioration during the warm-up period is the low temperature of the exhaust aftertreatment systems, where low temperature lowers their efficiency [11,[18][19][20]22,24]. ...
... Thus papers [12,[16][17][18]21,23,27] approach this issue for spark-ignition engines. The increase in the fuel dose during the engine cold start and the low temperature of the catalytic converter were recognized as the main causes responsible for the significant increase in the exhaust emission of hydrocarbons [16]. ...
Article
Full-text available
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.
... This might be particularly beneficial at low loads and/or when the engine has not yet warmed up, since incomplete combustion is likely to occur near relatively colder surfaces of the combustion chamber and the tailpipe emission of these chemical species cannot be cut down by the after-treatment system upon cold start, due to poor conversion efficiencies. Proper management and optimization of the engine behavior during warm-up is, therefore, of paramount importance [41], especially considering that a significant part of the car journeys is done after the vehicle has been parked for at least 3 to 8 h and may, thus, include a cold start as an unavoidable part of the daily driving [42]. However, in the published literature, there is only a small number of in-depth research studies on the interactions between engine thermal level and the combustion process, including an examination of the combined impacts of coolant temperature and the most important engine calibration parameters, such as exhaust gas recirculation (EGR) rate, injection time, rail pressure. ...
Article
Full-text available
To meet future goals of energy sustainability and carbon neutrality, disruptive changes to the current energy mix will be required, and it is expected that renewable fuels, such as hydrotreated vegetable oil (HVO), will play a significant role. To determine how these fuels can transition from pilot scale to the commercial marketplace, extensive research remains needed within the transportation sector. It is well-known that cold engine thermal states, which represent an inevitable portion of a vehicle journey, have significant drawbacks, such as increased incomplete combustion emissions and higher fuel consumption. In view of a more widespread HVO utilization, it is crucial to evaluate its performance under these conditions. In the literature, detailed studies upon these topics are rarely found, especially when HVO is dealt with. Consequently, the aim of this study is to investigate performance and exhaust pollutant emissions of a compression ignition engine running on either regular (petroleum-derived) diesel or HVO at different engine thermal states. This study shows the outcomes of warm-up/cool-down ramps (from cold starts), carried out on two engine operating points (low and high loads) without modifying the original baseline diesel-oriented calibration. Results of calibration parameter sweeps are also shown (on the same engine operating points), with the engine maintained at either high or low coolant temperature while combustion phasing, fuel injection pressure, and intake air flow rate are varied one-factor at a time, to highlight their individual effect on exhaust emissions and engine performance. HVO proved to produce less engine-out incomplete combustion species and soot under all examined conditions and to exhibit greater tolerance of calibration parameter changes compared to diesel, with benefits over conventional fuel intensifying at low coolant temperatures. This would potentially make room for engine recalibration to exploit higher exhaust gas recirculation, delayed injection timings, and/or lower fuel injection pressures to further optimize nitrogen oxides/thermal efficiency trade-off.
... Impact of cold temperature on the RDE In urban areas, a cold start can significantly contribute to vehicles' overall emissions and FC due to short trips and frequent starts [96]. Reduction in atmospheric temperature from 25 • C to 8 • C during a cold start (in the considered period of 300 s) resulted in a 16% rise in CO 2 (FC), a 195% rise in CO, a 280% rise in PN, and an 11% decrease in NO X [97]. ...
Article
Full-text available
Standard driving cycles (DCs) and real driving emissions (RDE) legislation developed by the European Commission contains significant gaps with regard to quantifying local area vehicle emission levels and fuel consumption (FC). The aim of this paper was to review local DCs for estimating emission levels and FC under laboratory and real-world conditions. This review article has three sections. First, the detailed steps and methodologies applied during the development of these DCs are examined to highlight weaknesses. Next, a comparison is presented of various recent local DCs using the Worldwide Harmonized Light-Duty Test Cycle (WLTC) and FTP75 (Federal Test Procedure) in terms of the main characteristic parameters. Finally, the gap between RDE with laboratory-based and real-world emissions is discussed. The use of a large sample of real data to develop a typical DC for the local area could better reflect vehicle driving patterns on actual roads and offer a better estimation of emissions and consumed energy. The main issue found with most of the local DCs reviewed was a small data sample collected from a small number of vehicles during a short period of time, the lack of separate phases for driving conditions, and the shifting strategy adopted with the chassis dynamometer. On-road emissions measured by the portable emissions measurement system (PEMS) were higher than the laboratory-based measurements. Driving situation outside the boundary conditions of RDE shows higher emissions due to cold temperatures, road grade, similar shares of route, drivers’ dynamic driving conditions, and uncertainty within the PEMS and RDE analysis tools. Keywords: driving cycle; emissions; PEMS; real driving emissions (RDE)
... Cold-start emission factors are an important indicator of the contribution of passenger car emissions to the urban areas. 35 They have recently been considered to have become one of the main sources of pollutants on Euro 6d-TEMP cars. 36 Hence, using cold-start emission factors in urban air quality models may be more representative of the real contribution of the passenger car sector in cities. ...
Article
Full-text available
Vehicles show higher emissions at cold temperature. Nevertheless, emissions during real world tests can be below Euro 6d-TEMP requirements. The relatively high PN emissions from gasoline and PHEV vehicles indicate there is still room for improvement.
... These conditions are unpredictable and can have a significant impact on the exhaust emission measurement results. However, according to data contained in publications, the thermal state of the vehicle (the engine) [10], average speed [11] driving dynamics [12] and road topography have the greatest impact on the achieved emission results. This means that the same vehicle but on different routes (meeting the requirements of the RDE test) will obtain different exhaust emission results. ...
... Cold start period is included in the whole RDE test (especially in the urban part of the test) [12]: ...
Article
Full-text available
In order to better reflect the actual ecological performance of vehicles in traffic conditions, both the emission standards and the applied emission tests are being developed, for example by considering exhaust emissions for a cold engine start. This article presents the research results on the impact of ambient temperature during the cold start of a gasoline engine in road emission tests. The Real Driving Emissions (RDE) tests apply to passenger cars that meet the Euro 6 emissions norm and they are complementary to their type approval tests. A portable emissions measurement system was used to record the engine and vehicle operating parameters, as well as to measure the exhaust emissions during tests. This allowed for parameters such as engine load, engine speed and vehicle speed to be monitored. The cold start conditions for two different temperatures (8°C and 25°C) were compared in detail. Moreover, the engine operating parameters, exhaust concentration values and road emissions for the 300 s time interval, were compared. The summary of the article presents the share of a passenger car’s cold start phase for each exhaust compound in the urban part of the test and in the entire Real Driving Emissions test depending on the ambient temperature.
... From September 2020, RDE emissions of new car models need to meet an NTE (Not-To-Exceed) emissions limit and the conformity factor for NOx emissions equal to 1.43 (an extra 43 per cent tolerance in emission value compared to the current NOx limit of 60 mg/km -in the case of a spark-ignition engine). Package 3 introduced both conformity factor for particle number and RDE cold start emissions [14,16]: ...
Article
Full-text available
The article presents the particulate emission measurements of passenger cars that meet the latest emission norms, the development of which has so far been dictated by requirements of downsizing. The comparison was made based on the selected vehicles equipped with spark-ignition engines, which are an example of reducing the displacement volume while maintaining the operational parameters of the drive units. Particle emissions were measured during tests in real traffic conditions. The change in the vehicle's emission category caused an increase in requirements regarding emitted particles number from these engines. As a result, the introduction of particulate filters into exhaust after-treatment systems of gasoline engines (so far only three-way catalytic converters have been used) became necessary. Comparisons of the mass and particles number and their dimensional distribution for vehicles of different ecological classes, and also engines before and after downsizing were the basis for making conclusions about the direction of changes in traditional propulsion units in modern vehicles.
... Low operating temperatures of aftertreatments are present during cold start and appear at low loads during warm-engine driving. Cold start primarily occurs in urban areas (Weiss et al., 2017), particularly in most local and populated streets (Faria et al., 2018), which is important for urban air quality. During cold start, the catalysts require to attain the light-off conditions, which is signified by the point at which the catalyst acquires a sufficiently high temperature to enable chemical reactions (Bannister and Taylor, 2014). ...
... Additionally, Euro 6 vehicles were studied in regulated driving cycles and real-world driving conditions (Dardiotis et al., 2013;Faria et al., 2018;Luján et al., 2018;Myung et al., 2017;Suarez-Bertoa et al., 2019;Valverde et al., 2019;Weber et al., 2019). Finally, the boundary conditions that affect the cold start of Euro 6 vehicles were related to ambient temperature (Chong et al., 2018;Grange et al., 2019;Suarez-Bertoa and Astorga, 2018), parking time, and other variables (Favez et al., 2009;Weiss et al., 2017). ...
Article
Exhaust aftertreatment systems are crucial to ensuring real-world NOx emission limits for motor vehicles. Operating conditions constrain the NOx reduction performance of aftertreatment devices. This study analysed real-world NOx emissions, tailpipe exhaust gas temperatures, and air-fuel ratios during cold start in a closed-loop urban route, followed by hot-start real driving emissions (RDE) tests. Five Euro-6b sport utility vehicles (SUV) were tested: two gasoline vehicles with three-way catalyst (TWC), namely, one gasoline direct injection (G-DI) and one hybrid electric vehicle (HEV); three diesel vehicles with different NOx control systems, namely, only exhaust gas recirculation (EGR), lean-burn NOx trap (LNT), and selective catalytic reduction (SCR). The only-EGR- and LNT-equipped diesel vehicles and the G-DI vehicle surpassed the NOx Euro 6 limits in all tested sections. For the same vehicles, the total RDE emission factors were 9.0, 7.4, and 5.0 times the Euro 6 limits, respectively. In contrast, the diesel vehicle with SCR had an RDE emission factor 1.0 times the limit, and the HEV exhibited very low emissions at approximately 2 mg NOx km⁻¹. However, during the cold start phase (first 5 min), the emission levels of the SCR and HEV vehicles surpassed the Euro 6 limits by 2.7 and 1.1 times, respectively. Based on the measurements at the tailpipe, the results indicate that cold start, urban driving, and cooling conditions of aftertreatment devices can lead to a decrease in the NOx conversion efficiency of TWC and SCR systems. The air-fuel ratio was key for the NOx conversion in TWC aftertreatment. The large differences between G-DI and HEV vehicles were primarily attributed to the lean and rich operations of the G-DI and HEV engines, respectively. To comply with stringent future regulations, lean-burn engines would require diesel-like aftertreatment. SCR and hybrid vehicles would require a careful aftertreatment thermal management or heat- ing to further exploit their potential for reducing emissions in urban areas.
... It is estimated that up to 80% of journeys in Europe are less than 10 km [1], while in the US the average vehicle trip is approximately 15 km [2]. Such short distances mean that a third of all trips are completed before the engine can achieve a fully warmed-up operation [3] The highest particulate matter (PM) concentration is produced during the first 100 seconds of the engine's operation, when the temperature of the fuel, piston and the cylinder's walls can be as low as −10 to −20 o C [4][5][6][7], accounting for up to 60% of the total PM drivecycle emissions [8]. Consequently, most of the vehicle emissions are produced while the engine is performing at suboptimal conditions, before the exhaust system's Three-Way Catalyst (TWC) has achieved light-off. ...
Conference Paper
The present work investigates the in-nozzle phenomenology of cold fuel injections. Large Eddy Simulations (LES) were performed using a 3D model of a step nozzle injector with water and iso-octane serving as working fluids and the examined cases spanning across a range of temperatures that is relevant to an engine’s start-up operation. The aim is to shed light on the influence exerted by temperature on the in-nozzle cavitation mechanism, which in turn affects the primary atomization and the structure of the downstream emerging spray. Results suggest that a decrease in the injected fuel’s temperature induces a reduction of the nozzle’s void fraction and a shrinkage in the streamwise length of the cavitation region. This suggests that the size and intensity of the hydrodynamic cavitation features tend to become suppressed in cold conditions. The phenomenon appears to be driven by the temperature dependence of the injected fluid’s thermophysical properties, primarily the vapour pressure, with lower values hindering phase change.