Miller-Steuerzeiten für zukünftige Nutzfahrzeug-Dieselmotoren

Upcoming emission limits such as Euro VII will make it necessary to further reduce the NOx emission level of internal combustion engines while stricter CO2 limits demand lower fuel consumption. Early closing of the intake valves (Miller timing) leads to reduced combustion temperatures due to lower effective compression ratio, and therefore lower formation and emission of nitrogen oxides. Miller timing is frequently used in gasoline engines, while in Diesel engines it competes with exhaust gas recirculation (EGR). When both measures are applied simultaneously, this may lead to increased emission of soot using standard Diesel fuel, as combustion temperature and oxygen content of the charge become too low. This work shows the investigation of different intake valve timings on an externally supercharged single-cylinder heavy-duty Diesel engine, stationary operated with hydrogenated vegetable oil (HVO), oxymethylene ether (OME), and standard Diesel fuel (DF). The synthetic fuels have a higher cetane number than DF, which supports ignition at lower temperatures. Moreover, OME has a soot-free combustion, which allows an extension of the operating limits without increased emissions. The results show that especially with Miller timing a high-performance turbocharging system is crucial, since higher boost pressure is required to compensate for the filling losses due to the earlier intake closing. The application of a high EGR rate is limited in this case, leading to a trade-off between Miller timing and EGR. All fuels show a reduction in nitrogen oxides of up to 40% with an improved efficiency of more than 3% at a typical road-load point. Measures to reduce ignition delay were found to be necessary, especially for DF. For OME, increased soot formation does not occur when combining Miller timing with low rail pressure, reduced boost pressure or EGR, which promotes simultaneous application of the measures resulting in minimized emissions of nitrogen oxides.

Section: Introductionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

Potential of miller timing with synthetic diesel fuels on a single cylinder heavy-duty engine

Pöllmann

Härtl

Wachtmeister

2021

“…24 It has been shown for diesel engines that Miller timing can have a positive effect on NO X reduction while maintaining or even increasing the engine thermal efficiency. [25][26][27][28] Compared to EGR, however, less potential for NO X reduction was observed. 26,27 In addition, Miller timing for diesel fuel was found to have disadvantages with regard to other emissions, especially increased particulate emissions.…”

Section: Introductionmentioning

confidence: 99%

“…[25][26][27][28] Compared to EGR, however, less potential for NO X reduction was observed. 26,27 In addition, Miller timing for diesel fuel was found to have disadvantages with regard to other emissions, especially increased particulate emissions. 25,29 An investigation of Miller valve timing in combination with OME, hydrogenated vegetable oil (HVO) and standard diesel fuel showed that, in contrast to conventional diesel and HVO, no increased particulate emissions occur for OME, and the higher cetane number of OME and HVO counteracts the delayed ignition of Miller timing due to the low temperatures.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of strategies to optimize engine efficiency and NOx emissions with the synthetic diesel fuel oxymethylene ether

Pöllmann

Härtl

Jaensch

et al. 2023

The use of CO2-neutral synthetic fuels in internal combustion engines contributes to achieving climate targets. Since their combustion is still associated with pollutant emissions, current research is focusing on minimizing harmful emissions, as well as on improving the efficiency of the combustion. The soot-free combustion of the synthetic diesel fuel oxymethylene ether (OME) opens up new scopes for reducing the remaining pollutants, particularly nitrogen oxides (NOX). Catalytic aftertreatment of NOX is costly and may lead to the generation of further emissions such as nitrous oxide, making it necessary to further investigate engine-internal approaches of NOX reduction. This work shows the influence of various in-engine measures on emissions and efficiency for OME and hydrogenated vegetable oil (HVO) as paraffinic diesel fuel, performed on a 1.75 l single-cylinder research engine. An injector variation was carried out for OME to compensate for the reduced lower heating value by a higher nozzle flow rate, which increases efficiency, but also NOX emissions. The examination of the measures of increasing exhaust gas recirculation, lowering rail pressure, Miller valve timing and high compression ratio shows a significant reduction in nitrogen oxide emissions in each case. At the same time, there is an improvement in indicated efficiency for Miller valve timing and high compression ratio, and with OME, in contrast to HVO, also by reducing the rail pressure. With HVO, each measure increases particulate number by up to several orders of magnitude. For OME, none of the measures resulted in a deterioration of the low particulate emissions, which allows an intensified application and combination of the measures. For example, the simultaneous application of higher compression, early intake closing and decreased injection pressure reduces nitrogen oxide emissions by more than two-thirds and improves efficiency by 5% without increasing particulate emissions.

“…Even in commercial vehicles, a variable valve train already promotes an emission reduction using Miller cycles in combination with an efficient turbo charging concept. 7,14 Also a cylinder deactivation is already considered via a variable valve train in order to achieve a faster efficiency of the exhaust after-treatment system after a cold start. 15 Even the implementation of an additional opening of an outlet valve (second event) 16 and an advanced outlet phasing 7,17 for commercial vehicles is considered which will be addressed also in the present work but only for passenger car diesel engines.…”

Section: Introductionmentioning

confidence: 99%

A model-based and experimental approach for the determination of suitable variable valve timings for cold start in partial load operation of a passenger car single-cylinder diesel engine

Maniatis

Wagner

Koch

2018

A manipulation of the charge exchange allows controlling the amount of residual gas during engine warm-up. The residual gas during the warm-up phase leads to an increase of the exhaust gas temperature and supports to reach the exhaust after-treatment system operating temperature faster. In addition, the warm residual gas increases the combustion chamber temperature, which reduces the HC and CO emissions. However, fuel consumption increases. For that reason, such heating measures should be the best compromise of both, exhaust gas temperature increase and engine efficiency, in order to provide efficient heating strategies for passenger car diesel engines. Therefore, simulative and experimental investigations are carried out at the Institute of Internal Combustion Engines of the Karlsruhe Institute of Technology to establish a reliable cam design methodology. For the experimental investigations, a modern research single-cylinder diesel engine was set up on a test bench. In addition, a one-dimensional simulation model of the experimental setup was created in order to simulate characteristics of valve lift curves and to investigate their effects on the exhaust gas temperature and the exhaust gas enthalpy flow. These simulations were based on design of experiments (DoE), so that all characteristics can be used sustainably for modeling and explaining their influences on the engine operation. This methodology allows numerically investigating promising configurations and deriving cam contours which are manufactured for testing. To assess the potential of these individual configurations, the results obtained were compared with each other as well as with the series configuration. Results show that the combination of DoE and one-dimensional simulation for the design of camshaft contours is well suited which was also validated with experimental results. Furthermore, the potential of residual gas retention by favorable configurations with a second event already revealed in various publications could be confirmed with respect to exhaust gas temperature increase and engine efficiency.