Lean Combustion Analysis of a Plasma-Assisted Ignition System in a Single Cylinder Engine fueled with E85 2022-24-0034

Engine research community is developing innovative strategies capable of reducing fuel consumption and pollutant emissions while ensuring, at the same time, satisfactory performances. Spark ignition engines operation with highly diluted or lean mixture is demonstrated to be beneficial for engine efficiency and emissions while arduous for combustion initiation and stability. Traditional igniters are unsuitable for such working conditions, therefore, advanced ignition systems have been developed to improve combustion robustness. To overcome the inherent efficiency limit of combustion engines, the usage of renewable fuels is largely studied and employed to offer a carbon neutral transition to a cleaner future. For such a reason, both innovative ignition systems and bio or E-fuels are currently being investigated as alternatives to the previous approaches.

Within this context, the present work proposes a synergetic approach which combines the benefits of a biofuel blend, i.e. E85, in conjunction with a plasma-assisted ignition system, i.e. barrier discharge igniter. The presence of oxygen within the ethanol fuel molecules, together with the ignition promoters due to the barrier discharge, accelerate the flame speed thus enhancing combustion on-set and stability. E85 allows for a remarkable reduction of CO and unburned HC with respect to gasoline while the barrier discharge ensures stable combustion at lean and/or diluted conditions thus lowering fuel consumption and emissions of CO₂ and NOx.

Tests were carried out on a single cylinder optical access engine working under port fuel injection mode. A combustion and performance metrics comparison with a conventional spark igniter is performed either in gasoline or E85. The engine was operated with different air-fuel ratios up to the lean stable limit for each combination of igniter and fuel. The combustion analysis exploits a simultaneous collection of indicating and imaging data as well as raw emissions of nitrogen oxides.