M. Prager

On the Dynamic Thermal System Behavior of a Glow Plug

In this paper the thermal system behavior of a glow plug is examined based upon its thermal impedance. The glow plug is a passive and low ohmic device as well as a rather slow sensor this is accounted for by the presented measurement setup and the modality of the system excitation to determine the transfer functions. The impact of the ambient temperature and the surrounding conditions on the thermal impedance is addressed as well. Since the glow plug is directly exposed to the combustion process it can be used as a sensor, e.g. for misfire detection. The combustion causes measurable changes of the temperature dependent resistance. The amplitude of this small signal is influenced by occurring aging processes. They can be compensated by determining the thermal impedance.

The Effect of Inlet Valve Timing and Engine Speed on Dual Fuel NG-Diesel Combustion in a Large Bore Engine

High load (18 bar IMEP) dual fuel combustion of a premixed natural gas/air charge ignited by directly ninjected diesel fuel was studied in a large bore gas engine. A nozzle design with low flow rate was ninstalled to inject a small diesel volume (10.4 mm3) equal an energetic amount of about two percent. nThe effect of compression end temperature on ignition and combustion was investigated using valve ntimings with early IVC (Miller) and maximum charging efficiency (MaxCC). Furthermore, the engine nspeed was reduced (1500 rpm to 1000 rpm) for the Miller valve timing to analyze the impact of the nchemical time scale on the combustion process. During all experiments, the cylinder charge density nwas kept constant adjusting the intake pressure and the resulting air mass flow. Unlike a typical nreactivity-controlled compression ignition (RCCI) combustion process, the combustion phasing of nthe investigated pilot-ignited natural gas combustion was also sensitive to the injection timing nbesides the air-fuel equivalence ratio (AFER). As a consequence of the lower compression end ntemperature with Miller valve timing, the operating range of the AFER was shifted to significantly nlower values (λ = 1.53 to 1.63) compared to MaxCC (λ = 1.88 to 2.08) and knocking combustion was nno longer observed. Furthermore, the bijective relation between the mass fraction burnt 50% n(MFB50%) as a function of the start of energizing (SoE) at a constant air-fuel equivalence ratio was nno longer valid. The experiments with MaxCC valve timing revealed that this behavior is not necessarily na characteristic of the pilot ignition. In fact, conditions inhibiting the ignition and engine knock nresult in loss of the one-to-one pairing between SoE and MFB50%. The reduction of the engine nspeed extended the lean misfire limit (λ = 1.53 to 1.75) and improved the engine start behavior.