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.

With alternative fuels having moved more into market in light of their reduction of emissions of CO2 and other air pollutants, the spark ignited internal combustion engine design has only been affected to small extent. The development of combustion engines running on natural gas or Biogas have been focused to maintain driveability on gasoline, creating a multi fuel platform which does not fully utilise the alternative fuels' potential. However, optimising these concepts on a fundamental level for gas operation shows a great potential to increase the level of utilisation and effectiveness of the engine and thereby meeting the emissions legislation. The project described in this paper has focused on optimising a combustion concept for CNG combustion on a single cylinder research engine. The ICE's efficiency at full load and the fuels characteristics, including its knock resistance, is of primary interest - together with part load performance and overall fuel consumption. In the process of increasing the efficiency of the engine the following areas have been of primary interest, increased compression ratio, thermal load at high cylinder pressure and the use of EGR to further increase efficiency. The overall goal in the project was to reduce the CO2-emissions while maintaining the performance and characteristics of the engine. The ambition is to reduce specific tail-pipe CO2-emissions in g/kWh by 50% compared to a modern gasoline engine. The goal was close to being reached at 45% reduction at full load and 25-34% on part load. This was done by theoretically downsizing the engine and increasing the specific performance of the engine.

Spark Ignition (SI) engines operating on stoichiometric mixtures can employ a simple three-way catalyst as after-treatment to achieve low tailpipe emissions unlike diesel engines. This makes heavy duty (HD) SI engines an attractive proposition for low capital cost and potentially low noise engines, if the power density and efficiency requirement could be met. Specific torque at low speeds is limited in SI engines due to knock. In HD engines, the higher flame travel distances associated with higher bore diameters exacerbates knock due to increased residence time of the end gas. This report reviews the challenges in developing HD SI engines to meet current diesel power density. It also focuses on methods to mitigate them in order to achieve high thermal efficiency while running on stoichiometric condition. High octane renewable fuels are seen as a key enabler to achieve the performance level required in such applications. Apart from higher octane rating, the effect of higher latent heat of vaporization in liquid alcohol fuels was found to be beneficial in all operating conditions as it tended to reduce in-cylinder temperature and associated heat loss of the engine. Exhaust gas recirculation (EGR) was seen to be beneficial both at full load in limiting knock and part load conditions to decrease pumping losses. Increased in-cylinder turbulence was also seen to be beneficial in limiting knock as it reduces residence time of the end gas. Results and trends of combinations of these factors are discussed with respect to increasing engine specific torque and efficiency. The effect on emissions and part load conditions is included where results are available and gaps in knowledge are presented. 

Gaseous methane fuel for internal combustion engineshave proved to be a competitive source of propulsionenergy for heavy duty truck engines. Using biogascan even reduce the carbon footprint of the truck to near-zerolevels, creating fully environmentally friendly transport. Gasengines have already been on the market and proved to be apopular alternative for buses and waste transport. However,for long haulage these gas engines have not been on par withthe equivalent diesel engines. To improve the power and efficiencyof EURO VI gas engines running stoichiometrically, adirect way forward is adding more boost pressure and sparkadvance in combination with more EGR to mitigate knock.Using in-cylinder turbulence to achieve higher mixing rate,the fuel can still be combusted efficiently despite the increasedfraction of inert gases. In this paper, previous findings onin-cylinder air flows for diesel engine simulations are investigatedfor the applicability on to stoichiometric gas combustion.Two key parameters were identified, swirl and squish.By varying the levels of swirl with different squish lengths inthe piston design, the in-cylinder flow motion is altered toinvestigate its effect on stoichiometric gas combustion. Thetesting was performed on a single cylinder research engineoperated in the equivalent multi cylinder engine operatingpoints. The results show that previous modelling findings areverified on the pre-mixed gas combustion studied. By choosingswirl and squish for the design of the gas engine, it is possibleto increase the combustion speed and thus the fraction of EGRin the combustion charge, without the latter having a negativeimpact on the combustion.

Clean combustion is one of the inherent benefits of using a high methane content fuel, natural gas or biogas. A single carbon atom in the fuel molecule results, to a large extent, in particle-free combustion. This is due to the high energy required for binding multiple carbon atoms together during the combustion process, required to form soot particles. When scaling up this process and applying it in the internal combustion engine, the resulting emissions from the engine have not been observed to be as particle free as the theory on methane combustion indicates. These particles stem from the combustion of engine oil and its ash content. One common practice has been to lower the ash content to regulate the particulate emissions, as was done for diesel engines. For a gas engine, this approach has been difficult to apply, as the piston and valvetrain lubrication becomes insufficient. However, the low particle emissions from the combustion of CNG does allow for an investigation of particle contribution from engine oil ash content with only a minor particle contribution from the fuel itself. The hypothesis for this study is that there is a relationship between the engine oil ash content and the particulate emissions from a CNG engine. The investigation was conducted for several operating points with varying engine speeds and load on a single cylinder engine. The single cylinder approach was chosen to reduce sources of engine oil intrusion in the combustion chamber. The obtained results were not in line with the hypothesis, the particle emissions from the lower ash content oil did not decrease in number but the size of the particles did. The results also showed a spiking behavior in the particulate emissions, originating from the lubrication oil consumption past the piston rings. Mass flow through the engine proved to affect the particle size distribution as well as the total number of particles for all levels of oil ash content.