Piston bowl geometry LORIN (M. Korkmaz)

Test bench setup LORIN (M. Korkmaz)


The worldwide rise in energy demand on the one hand and the concerns about harmful emissions of internal combustion engines (ICE) on the other hand, has led many researchers to focus on alternative fuels as well as on advanced combustion strategies. One approach to address these combined needs is the diesel dual-fuel (DDF) concept. In the DDF operation, two fuels with different auto-ignition characteristics are employed. A low-reactivity fuel, e.g. natural gas, is injected in the intake manifold (enabling uniformly mixing with air) and a high-reactivity fuel, e.g. diesel fuel, is directly injected into the combustion chamber (triggering the combustion). With this approach, it is possible to promote a homogeneous mixture, due to increased ignition delay time, which can lead to a simultaneous reduction of nitric oxides (NOx) and particulate matter (PM) emissions.

In this work, in-cylinder fuel blending based on premixed methane / air-mixture and direct injection of diesel fuel is investigated. Methane is chosen as a supplement to diesel fuel, due to its benefits like higher knock resistance, cleaner combustion, availability, higher auto-ignition temperature, and lower cetane number in comparison to diesel fuel. Moreover, the different combustion modes, which occur depending on the injection timing of the diesel fuel (early branch and late branch) and their impact on the performance metrics are analyzed.

A modified single-cylinder engine (SCE) that is based on a DV6 TED4 production engine is employed. For the DDF investigations, the compression ratio is reduced from 17.4:1 to 15.1:1 and the piston bowl geometry is changed from a re-entrant type to a flat piston bowl geometry. The relevant engine and injector parameters are listed in Table 1 and a schematic test bench layout is illustrated in Figure 1.

Table 1: Engine and injector specifications.

Figure 1:Schematic test bench layout.

For maintaining well-defined boundary conditions, the test bench is equipped with oil, water, and fuel conditioning systems. The air supply is ensured by an external charger unit and the desired intake air temperature is provided by the external heater. The load is represented by a DC motor (speed-controlled) equipped with a torque meter. For controlling the engine (i.e., intake pressure, exhaust pressure, injection timing, duration, cylinder pressure, etc.), a customized engine control unit (ECU) is used. The gas pressures are metered with piezoresistive sensors and the gas temperatures are measured with thermocouples, which are placed within the manifolds. The exhaust gas is collected using a heated probe and emissions data including NOx, THC, CO, CO2, O2, and PM were metered in the appropriate analyzers. Measurements of the air-fuel-ratio (AFR) were performed by the EGR 5230 module. The SCE is equipped with a piezoelectric pressure transducer (mounted via a glow plug adapter) in conjunction with the charge amplifier. Hereby, reliable thermodynamic data determination is ensured. The analysis of in-cylinder parameters, e.g., indicated mean effective pressure of the high-pressure process (IMEPHP), combustion phasing (CA50), and heat release rate (HRR) are evaluated in a thermodynamic real-time analysis module (TRA) for 100 consecutive cycles.

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