In heavy-duty engines, Euro VI legislation regulates the total particle number (PN) in the exhaust based on the particle measurement program (PMP) guidelines. By PMP directives, the exhaust sample is diluted and conditioned to contain non-volatile particles before measuring the PN. The fraction of non-volatile and volatile particles changes along the exhaust after-treatment system and could affect the total PN measured. Therefore, it is of interest to compare the performance of the dilution systems at different positions along the after-treatment system. For this purpose, a standard PMP compliant two-stage dilution system (DS1) with evaporation tube (ET) was compared with a close coupled two-stage ejector dilution system (DS2). In DS2, the non-volatile PN was measured with a dilution temperature of 350°C (same as the DS1 ET temperature) while the volatile PN was measured with a dilution temperature of 150°C. Experiments were carried out on a heavy-duty Euro VI engine equipped with an after-treatment system consisting of diesel oxidation catalyst (DOC), diesel particulate filter (DPF) and selective catalytic reduction (SCR) unit (with AdBlue injection) followed by ammonia slip catalyst. Sampling was made at four locations along the exhaust after-treatment system while varying the exhaust conditions namely temperature, flow rate and fuel injection pressure to vary the total PN concentration and the fraction of nucleation and accumulation mode particles from the engine. The total PN was measured using a condensation particle counter (CPC) and the particle number distribution using an Engine Exhaust Particle Sizer spectrometer (EEPS). An overall comparison shows that at higher fractions of nucleation mode particles, before the DPF, DS1 exhibited losses in nucleation mode particle in comparison with DS2. Whereas after the DPF, the loss was minimal. After the SCR, the nucleation of salt particles during excess AdBlue injection events was captured only by DS1. During motoring operation, emitting high volatile particle concentration, DS2's capacity does not seem to suffice to fully evaporate the volatile material as DS2 relies on the heat capacity of hot dilution air whereas DS1 uses an externally powered heater.

The ignition dynamics of an ethanol-diesel direct injection compression ignition engine is investigated based on 3D RANS simulations. Experimental results of a previous test campaign on a single-cylinder research engine equipped with two direct injectors are used to validate the CFD model. Four reference engine conditions are considered, including split and overlapped injections of ethanol and diesel at low and high load. Combustion driven by the separate direct injection of pure ethanol and diesel as pilot fuel is simulated with AVL Fire and AVL Tabkin adopting the flamelet generated manifold combustion model. The in-cylinder pressure and apparent rate of heat release traces computed in the simulations are found to be consistent with the corresponding experimental results. The influence of several simulation input parameters on ethanol combustion characteristics is evaluated, highlighting a high sensitivity to the initial in-cylinder temperature and a limited impact of the swirl number. The spatial and temporal interaction between ethanol and diesel sprays during ignition is investigated based on simulation results of in-cylinder flow features. Under the engine conditions considered in this study, ethanol ignition is found to originate within the spray plumes adjacent to the burning diesel sprays and to subsequently propagate towards the other ethanol sprays. The peak sequence identified in the ARoHR traces of experiments and simulations corresponds to the ignition sequence of the ethanol sprays. The coupling between experimental and simulation results allowed to achieve a detailed understanding of the ignition dynamics of an ethanol-diesel DICI engine. The validated simulation model will enable the performance evaluation of alternative hardware configurations of the dual-injector system.

In order to mitigate the effect of fossil fuels on global warming, biodiesel is used as drop in fuel. However, in the mixture of biodiesel and diesel, soft particles may form. These soft particles are organic compounds, which can originate from the production and degradation of biodiesel. Further when fuel is mixed with unwanted contaminants such as engine oil the amount soft particles can increase. The presence of these particles can cause malfunction in the fuel system of the engine, such as nozzle fouling, internal diesel injector deposits (IDID) or fuel filter plugging. Soft particles and the mechanism of their formation is curtail to understand in order to study and prevent their effects on the fuel system. This paper focuses on one type of soft particles, which are metal soaps. More precisely on the role of the short chain fatty acids (SCFA) during their formation. In order to do so, aged and unaged B10 was studied. The fuel matrixes were mixed with a calcium source such as calcium oxide (CaO), calcium carbonate (CaCO3) and engine oil. The importance of SCFA was studied by influencing the presence of the acids, by degrading the fuel, by the addition of formic acid and by inert gas bubbling. The created deposits and fuels mixtures were examined with the use of pH measurements, Fourier-transform infrared spectroscopy (FTIR), gas chromatography-mass spectrometry (GC-MS) and ion chromatography (IC). Opposed to the expectations, the results indicate that SFCA in not the most important factor for the formation of soft particles. It is shown that the calcium sources influenced the consistency and amount of the created soft particles. From the tested contaminants, CaO showed the highest yield towards precipitates. While degradation of the fuels showed to be the most important factor to form soap type soft particles.

Thanks to its properties and production pathways, ethanol represents a valuable alternative to fossil fuels, with potential benefits in terms of CO₂, NO_x, and soot emission reduction. The resistance to autoignition of ethanol necessitates an ignition trigger in compression-ignition engines for heavy-duty applications, which in the current study is a diesel pilot injection. The simultaneous direct injection of pure ethanol as main fuel and diesel as pilot fuel through separate injectors is experimentally investigated in a heavy-duty single cylinder engine at a low and a high load point. The influence of the nozzle hole number and size of the diesel pilot injector on ethanol combustion and engine performance is evaluated based on an injection timing sweep using three diesel injector configurations. The tested configurations have the same geometric total nozzle area for one, two and four diesel sprays. The relative amount of ethanol injected is swept between 78 – 89% and 91 – 98% on an energy basis at low and high load, respectively. The results show that mixing-controlled combustion of ethanol is achieved with all tested diesel injector configurations and that the maximum combustion efficiency and variability levels are in line with conventional diesel combustion. The one-spray diesel injector is the most robust trigger for ethanol ignition, as it allows to limit combustion variability and to achieve higher combustion efficiencies compared to the other diesel injector configurations. However, the two- and four-spray diesel injectors lead to higher indicated efficiency levels. The observed difference in the ethanol ignition dynamics is evaluated and compared to conventional diesel combustion. The study broadens the knowledge on ethanol mixing-controlled combustion in heavy-duty engines at various operating conditions, providing the insight necessary for the optimization of the ethanol-diesel dual-injection system.

Particles emitted from internal combustion engines have adverse health effects and the severity varies based on the particle size. A diesel particulate filter (DPF) in the after-treatment systems is employed to control the particle emissions from combustion engines. The design of a DPF depends on the nature of particle size distribution at the upstream and is important to evaluate. In heavy-duty diesel engines, the turbocharger turbine is an important component affecting the flow and particles. The turbine wheel and housing influence particle number and size. This could potentially be used to reduce particle number or change the distribution to become more favourable for filtration. This work evaluates the effect of a heavy-duty diesel engine's turbine on particle number and size distribution. The particle number (PN) emissions is measured with regard to varying turbine inlet conditions namely: turbine inlet temperature, exhaust mass flow rate and particle concentration at the turbine inlet (by varying fuel injection pressures). It was found that at turbine inlet temperatures of 200°C, PN remains almost constant as the particles were assumed to be held together by the volatile material. However, at 300°C there was an increase in PN across the turbine, and the increase was higher at higher mass flow rates across the turbine. Furthermore, lower injection pressures exhibited a higher rise in PN across the turbine. Interestingly, at 400°C, a reduction in PN across the turbine was observed due to oxidation. This reduction in PN was lesser while there was an increase in mass flow rate. Additionally, with higher injection pressures, a higher reduction in PN was noticed. This result is promising as catalyst coated turbine wheels could potentially enhance the effect thereby reducing PN before the after-treatment system.

Alcohols offer high resistance to autoignition which is necessary to attain the required load in heavy duty (HD) spark ignition (SI) engines. Dilution increases thermal efficiency and reduces propensity to autoignition making it an important combustion strategy. Reliable and robust prediction at increased dilution is necessary to support development of high efficiency spark ignition engines and the transition to renewable fuels. A previous experimental study demonstrated 25 bar gross IMEPg for ethanol and methanol at λ=1.4 excess air ratio and over 48% indicated efficiency at λ=1.6 on a single cylinder engine. Based on this dataset, a semi-predictive model (SITurb) was fitted for a range of excess air ratios and engine loads. With the default model, poor accuracy was observed above λ=1.4. Ignition delay was incorrectly predicted at λ=1.6 and λ=1.8. To improve the prediction at high dilution, an improved laminar flame speed correlation was included which reduced the ignition delay error to within ±3 CAD over the range of tested excess air ratios. To improve prediction of burn duration at high dilution, the turbulent flame speed calibration constant was made dependent on dilution level similar to previous research. With both improvements, under ±5% error in IMEPg and under ±3 CAD error in burn duration was achieved at all dilution levels. Finally, the Douaud and Eyzat knock model was evaluated with respect to full load operation of ethanol and methanol and its agreement to knock limited phasing discussed. Semi-predictive models are simple to implement and will be instrumental in gas exchange modeling and optimization of HD SI engines using future alcohol fuels. This study provides the accuracy of standard models and improvements needed to predict performance at diluted conditions.

The negative impact of transport on climate has led to incentives to increase the amount of renewable fuels used in internal combustion engines (ICEs). Oxygenated, liquid biofuels are promising alternatives, as they exhibit similar combustion behaviour to gasoline. In this article, the effect of the different biofuels on engine efficiency, combustion propagation and emissions of a gasoline-optimised direct injected spark ignited (DISI) engine were evaluated through engine experiments. The experiments were performed without any engine hardware modifications. The investigated fuels are gasoline, four alcohols (methanol, ethanol, n-butanol and iso-butanol) and one ether (MTBE). All fuels were tested at two speed sweeps at low and mid load conditions, and a spark timing sweep at low load conditions. The oxygenated biofuels exhibit increased efficiencies, even at non-knock-limited conditions. At lower loads, the oxygenated fuels decrease CO, HC and NOx emissions. However, at mid load conditions, decreased volatility of the alcohols leads to increased emissions due to fuel impingement effects. Methanol exhibited the highest efficiencies and significantly increased burn rates compared to the other fuels. Gasoline exhibited the lowest level of PN and PM emissions. N-butanol and iso-butanol show significantly increased levels of particle emissions compared to the other fuels

Combustion engines and liquid fuels are likely to continue playing a central role in freight transportation with renewable fuels reducing carbon emissions. Ethanol and methanol are future renewable fuels with a knock resistance that make them suitable for heavy-duty (HD) spark ignition (SI) engines. This simulation work focuses on the potential for improving the efficiency of an ethanol- and methanol-fueled HD SI engine using early intake valve closing Miller valve timing. With Miller valve timing, the expansion ratio and thermodynamic efficiency can be increased while maintaining the same effective compression ratio. However, Miller timing requires increased boost pressure to retain the same trapped air mass and also suffers from reduced in-cylinder turbulence. Unlike previous simulation studies, a validated semi-predictive combustion model was used to resolve the implication of turbulence reduction on burn rate and its impediment in extracting higher thermodynamic efficiency with Miller timing discussed. The observed increase in burn duration adversely affected knock and the overall efficiency benefit from Miller timing. At stoichiometric conditions, a 2-3% increase in brake efficiency was observed with Miller timing by increasing the geometric compression ratio even with a relatively low turbocharger efficiency of 49%. At lean conditions, the increase in burn duration and pumping loss was significant for both fuels demanding a minimum turbocharger efficiency of 55% to gain an improvement in brake efficiency from Miller timing. If the degree of Miller timing is constrained by a single-stage turbocharger, Miller timing showed only a 0.7% point efficiency increase at lean conditions due to the reduced burn rate. If the burn rate can be increased, similar to 2.5% increase in brake efficiency can be achieved using Miller timing leading to over 48% brake efficieny for both fuels thus making the HD SI engine competitive to HD diesel engines.