World Harmonized Transient Cycle Research Articles

Experimental investigation of exhaust thermal management on NOx emissions of heavy-duty diesel engine under the world Harmonized transient cycle (WHTC)

The control strategies of exhaust thermal management is experimental investigation to reduce Nitrogen oxides (NOx) emission under the world Harmonized transit cycle (WHTC) in this paper. The exhaust temperature of the 59.3% working conditions is lower than 200 °C under the cold start WHTC, and the average temperature of which is 196 °C, the urea injection system is in the state of stopping in most of time under cold start WHTC. The effects of intake throttle valve opening on NOx emission, fuel and urea consumption were studied in steady conditions with medium and low load. The 15–20% opening of intake throttle valve could increase the exhaust temperature to more than 200 °C when the torque is less than 250 N·m. The NOx emission weighted value of the WHTC is reduced by 41.5%, which could meet the requirements of the Europe V emission regulations for WHTC test cycle, but the fuel economy increase slightly. The Diesel Oxidation Catalyst (DOC) could increase the NO2/NOx ratio in the exhaust gas effectively, and increase the NOx conversion efficiency in the temperature range of 200–400 °C, which reduce the NOx emission weighted value of the diesel engine under WHTC by 8.7%.

Simulation Study on Thermal Management Strategy to Achieve 99 % SCR Efficiency of a Heavy-Duty Diesel Engine over a Transient Cycle

In this study, NOx conversion characteristics of a urea selective catalytic reduction (SCR) system equipped on a heavy-duty diesel engine were evaluated through engine dynamometer bench tests over a scheduled world harmonized transient cycle (WHTC). Also, based on transient SCR simulations, the thermal management strategy to improve SCR NOx conversion efficiency was investigated. As a result, it was found that a selective increase in exhaust temperature at low temperature period would be a useful measure to increase SCR efficiency on WHTC mode. From the baseline SCR efficiency of around 98 % on WHTC mode, the current simulation results have shown that around 99 % level of SCR efficiency would be achievable by increasing exhaust temperatures with modifying diesel exhaust fluid (DEF) dosage. Another valuable contribution of this study is that the design guidelines for controlling exhaust temperature and DEF injection to obtain a target NOx conversion efficiency are presented for SCR systems of heavy-duty diesel engines on transient operating conditions.

Estimation of the Diesel Particulate Filter Soot Load Based on an Equivalent Circuit Model

In order to estimate the diesel particulate filter (DPF) soot load and improve the accuracy of regeneration timing, a novel method based on an equivalent circuit model is proposed based on the electric-fluid analogy. This proposed method can reduce the impact of the engine transient operation on the soot load, accurately calculate the flow resistance, and improve the estimation accuracy of the soot load. Firstly, the least square method is used to identify the flow resistance based on the World Harmonized Transient Cycle (WHTC) test data, and the relationship between flow resistance, exhaust temperature and soot load is established. Secondly, the online estimation of the soot load is achieved by using the dual extended Kalman filter (DEKF). The results show that this method has good convergence and robustness with the maximal absolute error of 0.2 g/L at regeneration timing, which can meet engineering requirements. Additionally, this method can estimate the soot load under engine transient operating conditions and avoids a large number of experimental tests, extensive calibration and the analysis of complex chemical reactions required in traditional methods.

Model Predictive Control of a Diesel Engine with Turbo Compound and Exhaust After-Treatment Constraints

In this work we consider air path control of a Volvo Heavy Duty 13L Diesel engine equipped with three air path actuators Exhaust Gas Recirculation Valve (EGV), Intake Throttle Valve (ITV), turbocharger Wastegate (WG), and a Turbo Compound (TC). The purpose of the TC device is to recover the waste heat energy to improve fuel efficiency. Thus, the motivation is to control the air path system and in particular the exhaust energy to achieve satisfaction of the Exhaust After-Treatment System (EATS) requirements and assess the fuel economy. For this purpose a commercially available industrial tool for Model Predictive Control (MPC) has been applied. The designed controller is integrated in a production Engine Electrical Control Unit (EECU) and tests are performed both in engine test bench and on-road. The results show that by coordination of the air path actuators utilizing advanced MPC framework it leads to improvements in the exhaust energy conversion which was measured by fuel reduction of 0.3% with maintained NOx levels in a World-Harmonized Transient Cycle (WHTC) compared to a Proportional Integral Derivative (PID) control scheme. The designed MPC controller reached mass production maturity level and had a similar margin to the EU6 emission regulation as the compared PID control scheme.

Evaluating the emissions and performance of two dual-mode RCCI combustion strategies under the World Harmonized Vehicle Cycle (WHVC)

This work compares the emissions and performance of two dual-mode reactivity controlled compression ignition (RCCI) combustion strategies under the World Harmonized Vehicle Cycle (WHVC), a chassis dynamometer version of the World Harmonized Transient Cycle (WHTC) test proposed by the EURO VI emission regulation for heavy-duty engines. The major difference between the two dual-mode combustion strategies investigated is that, while one of them relies on covering with conventional diesel combustion (CDC) the part of the map that cannot be covered by RCCI regime (RCCI/CDC dual-mode), the other does it relying on dual-fuel diffusion combustion (dual-mode dual-fuel).The influence of the gear shifting strategy on the emissions and performance over the WHVC is discussed first. Later, both dual-mode concepts are compared considering the optimal gear shifting strategy. The results suggest that dual-mode dual-fuel concept allows reducing the specific fuel consumption by 7% in average versus RCCI/CDC concept. Moreover, NOx emissions are around 87% lower with dual-mode dual-fuel, meeting the EURO VI requirements without the need for an SCR aftertreatment system. In counterpart, HC and CO emissions are near 2 and 10 times greater, respectively, for dual-mode dual-fuel than for RCCI/CDC.

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.

Influence of active control strategies on exhaust thermal management for diesel particular filter active regeneration

The control strategies of exhaust thermal management are the premise of achieving the regeneration for Diesel Particulate Filter (DPF). In steady conditions with medium and low load, the effects of active control strategies on exhaust thermal management were studied at the test bench, which include intake throttle valve opening, injection advance angle, injection pressure and post injection.Compared with full opening of intake throttle valve, the 15–20% opening of intake throttle valve could increase the exhaust temperature by about 140°C, decrease the NOx emission but deteriorated the Particulate matter (PM) emission and fuel consumption. The change of injection advance angle and injection pressure have little effect on the exhaust temperature, but have a great effect on the emissions of NOx, PM and the fuel consumption. Optimized matching of the injection advance angle and quantity of post injections improves the exhaust temperature by about 70°C. The World Harmonized Transient Cycle (WHTC) was used to evaluate the effect of improving exhaust temperature. WHTC experimental results indicated clearly that the exhaust temperature was effectively increased within the whole 1800s, especially in the idle and low load conditions.

Modeling and validation of turbocharged diesel engine airpath and combustion systems

The ultimate aim of this study is the development of an engine modeling approach that would facilitate the design of model-based control techniques for diesel engines. This will allow for the development of more generalized, modular control strategies for different engine types and sizes as opposed to the commonly practiced map-based engine control strategies that depend on maps and feedforward control and require lengthy modifications every time a change is made. Also, most engine modeling studies focus on either airpath or combustion systems, treating these models and their validation individually, and not as an integrated system as is actually the case. To address the need for more realistic models suitable for model-based control design, this study develops a combined airpath and combustion model for the engine, using analytical models wherever possible and derives a model with appropriate control inputs and outputs that could be used in a control scheme. The inclusion of the actuator dynamics of the Exhaust gas recirculation (EGR), variable geometry turbine (VGT), and Throttle (THR) valves in the airpath model and the consideration of nonlinearities in the combustion model allow for the development of a more thorough engine model, as well as the validation of subsystems and the whole integrated engine model using a complete World Harmonized Transient Cycle (WHTC). This test cycle finds limited use due to its challenging transients, and yet, is the demanded test cycle for emission regulations nowadays. These are unique aspects of this modeling study, the results of which indicate that the developed engine model could be used in control design and hardware-in-the-loop simulation (HILS) based engine control prototyping.

Comparison between Internal and External EGR Performance on a Heavy Duty Diesel Engine by Means of a Refined 1D Fluid-Dynamic Engine Model

The potential of internal EGR (iEGR) and external EGR (eEGR) in reducing the engine-out NOx emissions in a heavy-duty diesel engine has been investigated by means of a refined 1D fluid-dynamic engine model developed in the GT-Power environment. The engine is equipped with Variable Valve Actuation (VVA) and Variable Geometry Turbocharger (VGT) systems. The activity was carried out in the frame of the CORE Collaborative Project of the European Community, VII FP. The engine model integrates an innovative 0D predictive combustion algorithm for the simulation of the HRR (heat release rate) based on the accumulated fuel mass approach and a multi-zone thermodynamic model for the simulation of the in-cylinder temperatures. NOx emissions are calculated by means of the Zeldovich thermal and prompt mechanisms. As a first step, the model has been calibrated and assessed on the basis of experimental tests carried out on four characteristic operating conditions within the WHSC (World Harmonized Stationary Cycle). The considered engine points have been used to identify the optimal engine parameters on the basis of a DoE approach. As a second step, sweeps simulations centered on the previously considered operating points have been run for iEGR and eEGR in order to study the effects of these latter on combustion and NOx formation processes at steady-state conditions. Finally, a ramp from the WHTC (World Harmonized Transient Cycle) has been reproduced with both iEGR and eEGR modes and the engine performance have been compared in terms of fuel consumption, combustion and NOx emissions

Integrated Energy and Emission Management for Diesel Engines with Waste Heat Recovery Using Dynamic Models

Rankine-cycleWasteHeatRecovery (WHR)systems are promising solutions to reduce fuel consumption for trucks. Due to coupling between engine andWHR system, control of these complex systems is challenging. This study presents an integrated energy and emission management strategy for an Euro-VI Diesel engine withWHRsystem. This Integrated Powertrain Control (IPC) strategy optimizes the CO2-NOx trade-off by minimizing online the operational costs associated with fuel and AdBlue consumption. Contrary to other control studies, the proposed control strategy optimizes overall engine-aftertreatment-WHR systemperformance and dealswith emission constraints. Fromsimulations, the potential of this IPC strategy is demonstrated over a World Harmonized Transient Cycle (WHTC) using a highfidelity simulationmodel. These results are compared with a state-of-the-art baseline engine control strategy. By applying the IPC strategy, an additional 2.6%CO2 reduction is achieved compare to the baseline strategy, while meeting the tailpipeNOx emission limit. In addition, the proposed low-levelWHR controller is shown to deal with the cold start challenges.

Examination of PN emissions and size distributions of a hybrid city bus under real world urban driving conditions

Engine load-speed frequency map of a hybrid city bus, which operates on the routes of Sakarya Municipality, was compared with that of European Transient Cycle (ETC) and World Harmonized Transient Cycle (WHTC), which are the certification test cycles. It was observed that the hybrid city bus engine operates mostly at three main regions, which are idling (30% load and 750 rpm), motoring (0% load and 1200 rpm) and high load (80% load and 1800 rpm) conditions under real world urban driving conditions. However, engine load-speed frequency maps of the certification test cycles are significantly different and cannot represent the real world urban driving conditions of the hybrid city bus. Therefore, the Particle Number (PN) emissions of the hybrid city bus were investigated under real world urban driving conditions. The aims of work were to examine the effects of city bus hybridization on the particle emissions and develop PN emission factors. The PN concentrations and size distributions together with engine operating conditions were measured with a Particle Measurement Program (PMP) compliant system, which involves a condensation particle counter (CPC) and a particle sizer (EEPS). The measurements under real world urban driving conditions indicated that the emission factors of the hybrid city bus for the PN and Total PN are 8.99E+12 and 2.51E+13 #/kW-h, respectively. The PN size distribution measurements indicated that the particles up to approximately 20 nm are not very sensitive to changes in engine power and they are exist even during motoring conditions. But, the particles in the size range from 20 to 200 nm are very sensitive to sudden changes of the engine power.