Reaching the particle emissions regulatory limits for the combustion engine is a challenge for developers.Particle filters have been the standard solution to reduce particle emissions, but filters arelimited in storage capacity and need to be regenerated, a process emitting more carbon dioxide(CO2) as more fuel is consumed to regenerate the filter. In previous research, it was found that theengine can emit large spikes in particle numbers (PNs) under stationary operating conditions. Thesespikes were several orders of magnitude higher than for the base particle emissions level and occurredseemingly at random. The source of the spikes was believed to be the cylinder-piston-ring systemand as 50–99% of the particles stemmed from these spikes, the influence on the particle emissionsmade it an interesting investigation to find the root cause of it. The experiments were performedfor different piston ring loads, locked ring positions, and different oil compositions. The resultsindicate a possibility to control the PN emissions through the experiment alterations, with lockedpiston rings having the greatest influence at a higher load. There was no clear relation between ringrotation and flutter with the spikes observed. The locked piston ring configurations did indicate thering gap not to be the main contributor to the spiking as fully aligned gaps did not result in thehighest levels of particle emissions. Variations to the oil composition indicate that a high-volatilityoil will emit higher levels of small, sub-10 nm particles compared to the standard baseline oil. Ahigh-viscosity oil instead lowers the particle emissions, possibly due to the higher inner friction athigh temperatures reducing the oil ingress into the combustion chamber. The link between the PNspiking phenomenon and the oil pathway past the piston ring was not established through theexperiments reported in this publication.

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.

The diesel engine is still one of the most common and most efficient mobile energy converters. Nevertheless, it is troubled by many problems, one of them being nozzle coking. This is not a new problem; however, due to the introduction of more advanced injection systems and a more diverse fuel matrix, including biofuels, the problem has become more complex. The nozzle holes are also much narrower today than when the problem first appeared and are therefore more sensitive to coking. Two CEC sanctioned coking tests exist for diesel engines, but no universally accepted test for heavy duty engines. In this paper, tests have been performed with B10 doped with 1 ppm zinc on a single cylinder engine, based on a heavy duty engine, with the purpose to develop a simple accelerated coking test. To have relevance to real usage, the test was based on real engine load points from a high power Euro V engine calibration. The coking propensity was studied in an engine speed sweep at max load. Based on this, a repeatable, convenient, single load point, 6 hour test with a one hour soak time in the middle, that managed to produce significant coking, was established. The average nozzle temperature was measured to around 255 °C with a thermocouple instrumented injector. Coking was evaluated based on the measured power loss during the tests and validated in a flow rig were the nozzle was disassembled from the injector and the flow was measured separately before and after the coking tests to isolate the effects of nozzle coking. Since the start of the tests are is of major importance, to condition the engine is very important. Running the engine on half load was concluded not to have significant effect on nozzle coking. It was also found that overnight engine soak lead to on average an increase in power output of around 1.2 % and that shorter soak periods did not significantly influence the deposit build up.