A viable option to reduce global warming related to internal combustion engines is to use renewable fuels, for example methanol. However, the risk of knocking combustion limits the achievable efficiency of SI engines. Hence, most high load operation is run at sub-optimal conditions to suppress knock. Normally the fuel is a limiting factor, however when running on high octane fuels such as methanol, other factors also become important. For example, oil droplets entering the combustion chamber have the possibility to locally impact both temperature and chemical composition. This may create spots with reduced octane number, hence making the engine more prone to knock. Previous research has confirmed a connection between oil droplets in the combustion chamber and knock. Furthermore, previous research has confirmed a connection between oil droplets in the combustion chamber and exhaust particle emissions. However, the co-variation between oil originating particle emissions and knock has not been investigated. The current study examines the connection between knock and particle number in the exhaust, when running on fuel with low soot production. A single cylinder spark ignited heavy-duty engine was used. It was equipped with port fuel injection and fueled with methanol, which produces very little soot at lambda 1. Consequently, the measured exhaust particle numbers were assumed to origin essentially from engine oil. Three grades of oil, in combination with three piston ring configurations, were used to vary the amount of oil entering the combustion chamber. Results from knock limited operation at both medium and high engine load showed that an increased number of particles in the exhaust was associated with an increased likelihood of knock. The authors find the hypothesis that an increase in particle number correlates with an increase in auto-ignition tendency to be confirmed.

Accurate exhaust gas temperature (EGT) measurements are vital in the design and developmentprocess of internal combustion engines (ICEs). The unsteady ICE exhaust flow and thermal inertia of commonly used sheathed thermocouples and resistance thermometers require high bandwidth EGT pulse measurements for accurate cycle-resolved and mean EGTs. The EGT pulse measurement challenge is typically addressed using exposed thin-wire resistance thermometers or thermocouples.The sensor robustness to response tradeoff limits ICE tests to short durations over a few exhaust conditions. Larger diameter multiwire thermocouples using response compensation potentially overcomes the tradeoff. However, the literature commonly adopts weaker slack wire designs despiteindications of coated weld taut wires being robust. This study experimentally evaluates the thin-wirethermocouple design placed in the exhaust of a heavy-duty diesel engine over wide-ranging exhaust conditions for improving both sensor robustness and accuracy of the measured EGT. The assessed design parameters included the wire diameter (51 μm to 254 μm), the exposed wire length, and thewires placed slack or taut with coated weld faces. All taut wires with ceramic-coated weld faces endured over 3 h of engine operation, while similar diameter slack wires (51 μm and 76 μm) were sensitive to the exhaust condition and exposed wire length. Reducing the wire diameter from 76 μmto 51 μm significantly impacted response improvements as evidenced at certain test conditions bya peak-peak EGT increase of 92 °C, a mean EGT drop of 26 °C, and a doubling of the sensitivity ofmean EGT cycle-to-cycle variations to ±12 °C. Increasing the exposed wire length showed less significant response improvements. The Type-K thin-wire thermocouples showed negligible drift, thereby indicating the possibility of using smaller and longer wires built taut with coated weld facesfor improved accuracy of EGT measurements in ICEs.

Stoichiometric operation of a Port Fueled Injection (PFI) Spark-Ignited (SI) engine with a three-way catalytic converter offers excellent CO2 reduction when run on renewable fuel. The main drawbacks with stoichiometric operation are the increased knock propensity, high exhaust temperature and reduced efficiency. Knock is typically mitigated with a reactive knock controller, with retarded ignition timing whenever knock is detected and the timing then slowly advanced until knock is detected again. This will cause some cycles to operate with non-ideal ignition timing. The current work evaluates the possibility to predict knock using the measured and modelled temperatures at Inlet Valve Closing (IVC) and Top Dead Center (TDC). Feedback effects are studied beyond steady state operation by using induced ignition timing disturbances. The approach is based on a deterministic controller where the timing is advanced beyond steady state knock limited operation or vastly retarded to produce warmer residuals in the following cycle. The results indicate that for the current engine there is no feedback effect. Chemical kinetics explains the lack of feedback due to lack of reactivity at TDC conditions. The chemical kinetic study in conjunction with the established auto ignition models described by Livengood-Wu reveals that the charge mixture entered a region of reactivity around the 50% burned point. It was also found that knocking and non-knocking cycles can have overlapping thermodynamic trajectories but for knocking cycles there is less dispersion. The study uses a solver which corrects the IVC temperature to minimize the error between observed knock onset and the point where the Livengood-Wu expression reaches unity for a knocking cycle. The corrections were found to have a correlation to uncaptured evaporation effects. Combined experimental and modelling results were in line with previous findings, namely that cycle-to-cycle combustion variations are plausibly explained by early flame propagation.

Modern spark-ignited (SI) engines offer excellent emission reduction when operated with a stoichiometric mixture and a three-way catalytic converter. A challenge with stoichiometric compared to diluted operation is the knock propensity due to the high reactivity of the mixture. This limits the compression ratio, thus reducing engine efficiency and increasing exhaust temperature. The current work evaluated a model of conditions at inlet valve closing (IVC) and top dead center (TDC) for steady state operation. The IVC temperature model is achieved by a cycle-to-cycle resolved residual gas fraction estimator. Due to the potential charge cooling effect from methanol, a method was proposed to determine the fraction of fuel sourced from a wall film. Determining the level of charge cooling is important as it heavily impacts the IVC and TDC temperatures. This method is based on air flow measurement and comparing information from the compression event during a transient from fired to motored conditions, while keeping the intake density constant. Experiments were conducted on a high compression ratio (14:1) heavy duty (HD) single cylinder research engine (SCRE). The fuel was methanol, injected via port fuel injection (PFI). The results indicate that the latent heat of vaporization of the fuel is far from being fully utilized, due to inherent design limitations of the intake system. It was also found that charge cooling could be altered by utilizing features of the swirl optimized cylinder head, while the same features also hinted that some stratification was possible. Accurate estimation of the IVC state and the later thermodynamic evolution is important for any closed cycle analysis. The result from the IVC and TDC condition estimators indicate that it is possible to capture expected trends.

This study delves into the modelling of resistance wire thermometers (RWTs) within the applicationcontext of measuring the exhaust gas temperature pulse in internal combustion engines. The modelwas developed in a commercial simulation software utilizing the heat balance equation. Disparitieswere found between different model representations of the prongs due to differences in the heat transfer within the sensor, which impacts its expected dynamic response. The appropriate modelling choicewill be made upon validation with shock tube experiments for different RWT designs

This study revisits the design of resistance wire thermometers (RWTs) for measuring time-resolved temperature pulsations of the exhaust gas on internal combustion engines. RWTs with gold coated tungsten wires were fabricated and tested on a heavy-duty diesel engine. Experimental results indi-cate their utility in such harsh environments with the addition of a protective ceramic coating over the welded joints. The influence of the coating on sensor geometry and response will be elucidated through shock tube and gas stand experiments.

The possibility of non-volatile particle agglomeration in engine exhaust was experimentally examined in a Euro VI heavy duty engine using a variable cross section agglomeration pipe, insulated and double walled for minimal thermophoresis. The agglomeration pipe was located between the turbocharger and the exhaust treatment devices. Sampling was made across the pipe and along the centre-line of the agglomeration pipe. The performance of the agglomeration pipe was compared with an equivalent insulated straight pipe. The non-volatile total particle number and size distribution were investigated. Particle number measurements were conducted according to the guidelines from the Particle Measurement Programme. The Engine was fuelled with commercially available low sulphur S10 diesel. Experiments conducted in heavy duty engine relevant operating points were done to sweep the effect of (i) Mass flow rate in the exhaust (ii) Temperature in the exhaust and (iii) Engine speed and thus exhaust pressure pulsation frequencies in the exhaust. The test matrix included eleven operating points at steady-state. The results show that, using the agglomeration pipe, neither significant non-volatile particle reduction nor noticeable change in particle size distribution could be proven. In the current study, nucleation of non-volatile particles could not be observed along the straight pipe. Furthermore, it was found that the variable cross-section agglomeration pipe and straight pipe showed similar results in the total particle number and particle size distribution with respect to non-volatile particles.

To conduct system level studies on internal combustionengines reduced order models are required in order tokeep the computational load below reasonable limits.By its nature a reduced order model is a simplification of realityand may introduce modeling errors. However what is of interestis the size of the error and if it is possible to reduce the errorby some method. A popular system level study is gas exchangeand in this paper the focus is on the exhaust valve. Generallythe valve is modeled as an ideal nozzle where the flow lossesare captured by reducing the flow area. As the valve movesslowly compared to the flow the process is assumed to be quasisteady,i.e. interpolation between steady-flow measurementscan be used to describe the dynamic process duringvalve opening. These measurements are generally done at lowpressure drops, as the influence of pressure ratio is assumed tobe negligible. As it is very difficult to measure time-resolvedmass flow it is hard to test validity of these modeling assumptions.Experimental data indicates that the model overestimatesvalve flow during the blowdown event. As the blowdown pulsecontains a significant portion of the energy in the cylinder atexhaust valve opening, it is therefore of importance to modelthis correctly. In this paper experimental results from previouslypublished research have been compared to simulationresults and the deviation from quasi-steady behavior has beenquantified. The deviation appears to be a function of pressureratio over the valve and valve opening speed. A model isproposed to compensate for the observed effects.