Experiments and modeling of a dual-mode, turbulent jet ignition engine

Diesel engines use diffusion-controlled combustion of a high-reactivity fuel and offer high efficiencies because they combine lean combustion with a high compression ratio. For low-reactivity fuels such as gasoline or natural gas, premixed combustion is used, which leads to lower efficiency levels as usually stoichiometric combustion is combined with lower compression ratios. Trying to apply diesel-like process parameters to low-reactivity fuels inevitably leads to problems with classical spark ignition systems as they are not able to establish robust flame propagation for such hard-to-ignite conditions. One possibility to enable fast combustion for diluted mixtures at high pressure levels is to establish ignition in a prechamber and ignite the charge of the main combustion chamber using the turbulent jets exiting the prechamber. In this study, the experimental results of a prechamber-equipped four-cylinder natural gas engine with 2 L displacement are discussed in detail. In the majority of the engine map, auxiliary fueling is used in the prechamber and a global air–fuel equivalence ratio λ is set to 1.7. At full load, a λ of 1.5 is applied without auxiliary prechamber fueling. The experiments show that such a setup is able to achieve brake efficiency levels of above 45% while maintaining peak brake mean effective pressure levels above 20 bar. At high load conditions, cylinder pressure levels at ignition timing achieve more than 80 bar and cylinder peak pressures of around 180 bars occur. The technology proved to enable robust and very fast combustion at comparably low NOx levels. A remaining challenge for the on-road use of such a technology is the reduction of the methane emissions at lean conditions.

Section: Introductionmentioning

confidence: 99%

Efficient light-duty engine using turbulent jet ignition of lean methane mixtures

Soltic

Hilfiker

Hänggi

2019

“…Promising and advanced technological solutions have been suggested and explored to reach clean and efficient combustion in spark ignition (SI) engines, such as engine downsizing, 5 direct-injection with charge stratification, 6 lean mixture operation, 7,8 controlled auto-ignition, 9,10 water injection, [11][12][13][14] exhaust gas recirculation. 15,16 Innovative ignition strategies have been also proposed and explored, like plasma assisted ignition systems 17,18 or pre-chamber turbulent jet ignition, [19][20][21] homogeneous charge compression ignition (HCCI) 22,23 and reactivity controlled compression ignition (RCCI). 24,25 These advanced combustion concepts can improve engine efficiency by 10-20% 4,26 and simultaneously reduce pollutant emissions.…”

Section: Introductionmentioning

confidence: 99%

LES investigation of cycle-to-cycle variation in a SI optical access engine using TFM-AMR combustion model

Zembi

Battistoni

Nambully³

et al. 2021

Multi-cycle large-eddy simulations (LES) are performed to investigate combustion cycle-to-cycle variability (CCV) in a gasoline spark ignited optical access engine operating under homogeneous stoichiometric conditions. Combustion is addressed with the Thickened Flame Model (TFM) and finite rate chemistry is accounted for through a reduced oxidation reaction mechanism. In view of the fact that computational costs of LES engine simulations are still very high today, this work investigates the use of adaptive mesh refinement (AMR) in the flame zone in conjunction with the artificial flame thickening applied by the TFM model. The paper discusses how the resulting coupled TFM-AMR combustion model allows good resolution of the flame, maintaining accuracy at acceptable costs. First, the details of the coupled model are presented and the effects of the parameters are explored, highlighting their impact on the combustion prediction. Then, computational fluid dynamics (CFD) simulation results are validated against experimental data collected in a low-speed low-load engine point, by comparing 20 LES cycles and 100 measured cycles, for mass fraction burned, combustion phasing, flame images and CCV indices. Lastly, a detailed investigation on the fastest and slowest numerical cycles is presented, analyzing instantaneous flame structures, ignition behaviors, propagation speeds, and probability density function (PDF) of the instantaneous velocity fluctuation around the spark region. The results show that combustion variability is highly correlated to the resolved velocity field and the resolved turbulence intensity, which is found to be the main cause of CCV and affects the early flame kernel growth. This work is an early attempt to use TFM-AMR combustion model for LES simulations of internal combustion engines.

“…In the latter, an empirical multiplicative factor, varying with the nozzle exit velocity, is introduced to account for the enhancement of the mainchamber heat release rate by the turbulent jet, similarly to Tolou and Schock. 37 The latter model has been extended to liquid fuels and applied for the centre of combustion (CA-50) control for a prechamber gas engine. 36,38 In physics-based modelling approaches, [39][40][41][42] the flame propagation inside the prechamber is modelled based on a laminar flame surface and a turbulent flame speed.…”

Section: Introductionmentioning

confidence: 99%

Development and validation of a novel quasi-dimensional combustion model for un-scavenged prechamber gas engines with numerical simulations and engine experiments

Bardis

Kyrtatos²,

et al. 2020

Lean-burn gas engines equipped with an un-scavenged prechamber have proven to reduce nitrogen oxides (NOx) emissions and fuel consumption, while mitigating combustion cycle-to-cycle fluctuations and unburned hydrocarbon (UHC) emissions. However, the performance of a prechamber gas engine is largely dependent on the prechamber design, which has to be optimised for the particular main chamber geometry and the foreseen engine operating conditions. Optimisation of such complex engine components relies partly on computationally efficient simulation tools, such as quasi and zero-dimensional models, since extensive experimental investigations can be costly and time-consuming. This article presents a newly developed quasi-dimensional (Q-D) combustion model for un-scavenged prechamber gas engines, which is motivated by the need for reliable low order models to optimise the principle design parameters of the prechamber. Our fundamental aim is to enhance the predictability and robustness of the proposed model with the inclusion of the following: (i) Formal derivation of the combustion and flow submodels via reduction of the corresponding three-dimensional models. (ii) Individual validation of the various submodels. (iii) Combined use of numerical simulations and experiments for the model validation. The resulting model shows very good agreement with the numerical simulations and the experiments from two different engines with various prechamber geometries using a set of fixed calibration parameters.