TURBOCHARGING OF HIGH PERFORMANCE COMPRESSED NATURAL GAS SI ENGINE FOR LIGHT DUTY VEHICLE

Natural gas as an automotive fuel has many benefits in comparison with traditional fossil fuels. Favorable anti‐knock properties of methane allow us to utilize higher boost levels and the engine power than that of gasoline engines. High level of intake boosting make possible to achieve loads, comparable to the state‐of‐the‐art diesel of engines without soot and PM emission. Stoichiometric operation within the full range of the complete engine map enables the use of a relatively simple exhaust gas aftertreatment, based on a three‐way catalyst.The paper describes a chosen 1‐D thermodynamic modelling studies, calibrated and validated by experimental data. The investigations were performed on a spark ignition, direct injection, four‐cylinder engine with 1.6 L displacement. The engine was optimized for mono fuel operation with compressed natural gas.Due to complexity of gaseous fuel infrastructure in vehicles, compared to the traditional fuels, it is desirable to keep the turbocharging system as simple as possible. Traditional variable geometry turbine systems were tested. Practical design constraints as peak cylinder pressure, turbine inlet temperature, compressor outlet temperature and others were met. Various strategies on how to achieve high load at low engine speed were investigated.The authors propose a single stage turbocharger to cover the demand for a high torque at low engine speed and high power at full speed, with boost levels comparable to a dual stage turbocharging. It was concluded that the single stage turbocharging enables the engine to operate with maximum BME of 3 MPa between 1500 and 2750 rpm. Maximum engine speed had to be limited to a similar value that is usually applied in a diesel engine due to limited control range of turbocharging

Analysis of Pre-ignition Combustions Triggered by Heavy Knocking Events in a Turbocharged GDI Engine

Abstract In this paper, a pre-ignition sequence with detrimental effects on the engine has been analysed and described, with the aim of identifying the main parameters involved in damaging the combustion chamber components. The experiment was carried out in a wider research context, focused on knock damage mechanisms in turbocharged GDI engines. The pre-ignition sequence was a consequence of a high knock condition, induced at high load at 4500 rpm. The abnormal thermal load due to knock caused overheating of the whole combustion chamber, until the spark plug electrodes became a "hot spot", resulting in premature flame initiation in the following cycles, with a self-sustaining mechanism. Slight cylindrical differences, mainly in terms of volumetric efficiency, allowed comparisons and correlations between indicated parameters, pre-ignition sequence and damage. The main responsible in damaging the engine, in this case and for this engine, is the extremely high heat transferred to the walls in the pre-ignited cycles, characterized by higher mean temperatures. Heavy knock triggered the pre-ignited combustions but progressively reduced its intensity as the spontaneous ignition advance increased, thus having a secondary role in damaging directly the combustion chamber