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Lean-burn hydrogen internal combustion engines are a good option for future transportation solutions since they do not emit carbon-dioxide and unburned hydro-carbons, and the emissions of nitric-oxides (NOx) can be kept low. However, under lean-burn conditions the combustion duration increases, and the combustion stability decreases, leading to a reduced thermal efficiency. Turbulent jet ignition (TJI) can be used to extend the lean-burn limit, while decreasing the combustion duration and improving combustion stability. The objective of this paper is to investigate the feasibility of a passive pre-chamber TJI system on a heavy-duty hydrogen engine under lean-burn conditions using CFD modelling. The studied concept is mono-fuel, port-fuel injected, and spark ignited in the pre-chamber. The overall design of the pre-chamber is discussed and the effect of design parameters on the engine performance are studied.

This paper focusses on the application of bioalcohols (ethanol and butanol) derived from seaweed in Heavy-Duty (HD) Compression Ignition (CI) combustion engines. Seaweed-based fuels do not claim land and are not in competition with the food chain. Currently, the application of high octane bioalcohols is limited to Spark Ignition (SI) engines. The Reactivity Controlled Compression Ignition (RCCI) combustion concept allows the use of these low carbon fuels in CI engines which have higher efficiencies associated with them than SI engines. This contributes to the reduction of tailpipe CO2 emissions as required by (future) legislation and reducing fuel consumption, i.e. Total-Cost-of-Ownership (TCO). Furthermore, it opens the HD transport market for these low carbon bioalcohol fuels from a novel sustainable biomass source. In this paper, both the production of seaweed-based fuels and the application of these fuels in CI engines is discussed.

Butanol is an attractive alternative fuel by virtue of its renewable source and low sooting tendency. In this paper, three butanol isomers (n-butanol, isobutanol, and tert-butanol) were induced via port injection respectively and n-heptane was directly injected into the cylinder to investigate reactivity controlled compression ignition in a heavy-duty diesel engine. This work evaluates the potential of applying butanol as low reactivity fuel and the effects of reactivity gradient on combustion and emission characteristics. The experiments were performed from low load to medium-high load. Due to the different reactivities among the butanol isomers, the exhaust gas recirculation rate and the direct injection strategy were varied for a specific butanol isomer and testing load. Particularly, isobutanol/n-heptane can be operated with single direct injection and no exhaust gas recirculation up to medium load due to the high octane rating.

CO2 regulations on heavy-duty transport are introduced in essentially all markets within the next decade, in most cases in several phases of increasing stringency. To cope with these mandates, developers of engines and related equipment are aiming to break new ground in the fields of combustion, fuel and hardware technologies. In this work, a novel diesel fuel injector, Delphi’s DFI7, is utilized to experimentally investigate and compare the performance of ramped injection rates versus traditional square fueling profiles. The aim is specifically to shift the efficiency and NOx tradeoff to a more favorable position. The design of experiments methodology is used in the tests, along with statistical techniques to analyze the data. Results show that ramped and square rates - after optimization of fueling parameters - produce comparable gross indicated efficiencies.

N-butanol, as a biomass-based renewable fuel, has many superior fuel properties. It has a higher energy content and cetane number than its alcohol competitors, methanol and ethanol. Previous studies have proved that n-butanol has the capability to achieve lower emissions without sacrifice on thermal efficiency when blended with diesel. However, most studies on n-butanol are limited to low blending ratios, which restricts the improvement of emissions. In this paper, 80% by volume of n-butanol was blended with 20% by volume of n-heptane (namely BH80). The influences of various engine parameters (combustion phasing, EGR ratio, injection timing and intake pressure, respectively) on its combustion and emission characteristics are tested at different loads. The results showed that when BH80 uses more than 40% EGR, the emitted soot and nitrogen oxides (NOx) emissions are below the EURO VI legislation.

The accepted model of conventional diesel combustion [1] assumes a rich premixed flame slightly downstream of the maximum liquid penetration. The soot generated by this rich premixed flame is burnt out by a subsequent diffusion flame at the head of the jet. Even in situations in which the centre of combustion (CA50) is phased optimally to maximize efficiency, slow late stage combustion can still have a significant detrimental impact on thermal efficiency. Data is presented on potential late-stage combustion improvers in a EURO VI compliant HD engine at a range of speed and load points. The operating conditions (e.g. injection timings, EGR levels) were based on a EURO VI calibration which targets 3 g/kWh of engine-out NOx. Rates of heat release were determined from the pressure sensor data. To investigate late stage combustion, focus was made on the position in the cycle at which 90% of the fuel had combusted (CA90). An EN590 compliant fuel was tested.

Premixed Charge Compression Ignition concepts are promising to reduce NOx and soot simultaneously and keeping a high thermal efficiency. Partially premixed combustion is a single fuel variant of this new combustion concepts applying a fuel with a low cetane number to achieve the necessary long ignition delay. In this study, multiple injection strategies are studied in the partially premixed combustion approach to reach stable combustion and ultra-low NOx and soot emission at 15.5 bar gross indicated mean effective pressure. Three different injection strategies (single injection, pilot-main injection, main-post injection) are experimentally investigated on a heavy duty compression ignition engine. A fuel blend (70 vol% n-butanol and 30 vol% n-heptane) was tested. The effects of different pilot and post-injection timing, as well as Exhaust-gas Recirculation rate on different injection strategies investigated.

Post-injection strategies prove to be a valuable option for reducing soot emission, but experimental results often differ from publication to publication. These discrepancies are likely caused by the selected operating conditions and engine hardware in separate studies. Efforts to optimize not only engine-out soot, but simultaneously fuel economy and emissions of nitrogen oxides (NOx) complicate the understanding of post-injection effects even more. Still, the large amount of published work on the topic is gradually forming a consensus. In the current work, a Design-of-Experiments (DoE) procedure and regression analysis are used to investigate the influence of various operating conditions on post-injection scheduling and efficacy. The study targets emission reductions of soot and NOx, as well as fuel economy improvements. Experiments are conducted on a heavy-duty compression ignition engine at three load-speed combinations.

Recently introduced sulfur caps on marine fuels in so-called sulfur emission control areas (SECAs) are forcing shipping companies to sail on more or less automotive grade diesel in lieu of the considerably less expensive, but sulfur-laden heavy fuel oil (HFO) to which they were accustomed. This development is an opportunity for a bio-based substitute, given that most biomass is sulfur free by default. Moreover, given that biomass is typically solid to start with, cracking it to an HFO grade, which is highly viscous in nature, will involve fewer and/or less harsh process steps than would be the case if an automotive grade fuel were to be targeted. In this study, a renewable low sulfur heavy fuel oil (LSHFO) has been produced by means of subcritical water assisted lignin depolymerization in the presence of a short length surfactant, ethylene glycol monobutyl ether (EGBE).

The modeling of fuel sprays under well-characterized conditions relevant for heavy-duty Diesel engine applications, allows for detailed analyses of individual phenomena aimed at improving emission formation and fuel consumption. However, the complexity of a reacting fuel spray under heavy-duty conditions currently prohibits direct simulation. Using a systematic approach, we extrapolate available spray models to the desired conditions without inclusion of chemical reactions. For validation, experimental techniques are utilized to characterize inert sprays of n-dodecane in a high-pressure, high-temperature (900 K) constant volume vessel with full optical access. The liquid fuel spray is studied using high-speed diffused back-illumination for conditions with different densities (22.8 and 40 kg/m3) and injection pressures (150, 80 and 160 MPa), using a 0.205-mm orifice diameter nozzle.

In this work, the influences of aromatics on combustion and emission characteristics from a heavy-duty diesel engine under various loads and exhaust gas recirculation (EGR) conditions are investigated. Tests were performed on a modified single-cylinder, constant-speed and direct-injection diesel engine. An engine exhaust particle sizer (EEPS) was used in the experiments to measure the size distribution of engine-exhaust particle emissions in the range from 5.6 to 560 nm. Two ternary blends of n-heptane, iso-octane with either toluene or benzaldehyde denoted as TRF and CRF, were tested, diesel was also tested as a reference. Test results showed that TRF has the longest ignition delay, thus providing the largest premixed fraction which is beneficial to reduce soot. However, as the load increases, higher incylinder pressure and temperature make all test fuels burn easily, leading to shorter ignition delays and more diffusion combustion.

Cylinder pressure-based combustion control is widely introduced for passenger cars. Benefits include enhanced emission robustness to fuel quality variation, reduced fuel consumption due to more accurate (multi-pulse) fuel injection, and minimized after treatment size. In addition, it enables the introduction of advanced, high-efficient combustion concepts. The application in truck engines is foreseen, but challenges need to be overcome related to durability, increased system costs, and impact on the cylinder head. In this paper, a new single cylinder pressure sensor concept for heavy-duty Diesel engines is presented. Compared to previous studies, this work focuses on heavy-duty Diesel powertrains, which are characterized by a relatively flexible crank shaft in contrast to the existing passenger car applications.

Homogeneous Charge Compression Ignition (HCCI) combustion technology has demonstrated a profound potential to decrease both emissions and fuel consumption. In this way, the significance of the 2-stroke HCCI engine has been underestimated as it can provide more power stroke in comparison to a 4-stroke engine. Moreover, the mass of trapped residual gases is much larger in a 2-stroke engine, causing higher initial charge temperatures, which leads to easier auto-ignition. For controlling 2-stroke HCCI engines, it is vital to find optimized simulation approaches of HCCI combustion with a focus on ignition timing. In this study, a Computational Fluid Dynamic (CFD) model for a 2-stroke gasoline engine was developed coupled to a semi-detailed chemical mechanism of iso-octane to investigate the simulation capability of the considered chemical mechanism and the effects of different simulation parameters such as the turbulence model, grid density and time step size.

Styrene, or ethylbenzene, is mainly used as a monomer for the production of polymers, most notably Styrofoam. In the synthetis of styrene, the feedstock of benzene and ethylene is converted into aromatic oxygenates such as benzaldehyde, 2-phenyl ethanol and acetophenone. Benzaldehyde and phenyl ethanol are low value side streams, while acetophenone is a high value intermediate product. The side streams are now principally rejected from the process and burnt for process heat. Previous in-house research has shown that such aromatic oxygenates are suitable as diesel fuel additives and can in some cases improve the soot-NOx trade-off. In this study acetophenone, benzaldehyde and 2-phenyl ethanol are each added to commercial EN590 diesel at a ratio of 1:9, with the goal to ascertain whether or not the lower value benzaldehyde and 2-phenyl ethanol can perform on par with the higher value acetophenone. These compounds are now used in pure form.

A Gasoline Compression Ignition combustion strategy was developed and showed its capabilities in the heavy duty single cylinder test-cell, resulting in indicated efficiencies up to 50% and low engine out emissions applying to EU VI and US 10 legislations while the soot remained at a controllable 1.5 FSN. For this concept a single-cylinder CI-engine was used running at a lambda of ∼1.6 and EGR levels of ∼50% and a modified injection strategy. Part of this strategy was also the use of a gasoline blended with an ignition improver, giving the blend a cetane number in the range of regular diesel; ∼50. In this paper a step is taken towards implementation of this combustion concept into a multi-cylinder light duty standalone CI-engine. A standard CI-engine was modified so that its gas-exchange system could deliver the requested amounts of EGR and lambda.

In an earlier study, a novel type of diesel fuel injector was proposed. This prototype injects fuel via porous (sintered) micro pores instead of via the conventional 6-8 holes. The micro pores are typically 10-50 micrometer in diameter, versus 120-200 micrometer in the conventional case. The expected advantages of the so-called Porous Fuel Air Mixing Enhancing Nozzle (PFAMEN) injector are lower soot- and CO2 emissions. However, from previous in-house measurements, it has been concluded that the emissions of the porous injector are still not satisfactory. Roughly, this may have multiple reasons. The first one is that the spray distribution is not good enough, the second one is that the droplet sizing is too big due to the lack of droplet breakup. Furthermore air entrainment into the fuel jets might be insufficient. All reasons lead to fuel rich zones and associated soot formation.

A literature and experimental study was done to create an overview of the behavior of gasoline combusted in a CI-engine. This paper creates a first overview of the work to be done before implementing this Gasoline Compression Ignition concept in a multi-cylinder engine. According to literature the gasoline blend will have advantages over diesel. First the shorter molecular chain of the gasoline makes it less prone to soot. Second the lower density gives the gasoline a higher nozzle exit speed resulting in better mixing capabilities. Third the lower density and higher volatility lets the spray length decrease. This lowers the chance of wall-impingement, but creates worse mixing conditions looking from a spray point of view. The CO and HC emissions tend to increase relative to operation with diesel fuel, NOx emissions largely depend on the choice of combustion strategy and could be influenced by the nitrogen bound to the EHN molecule that is used as an ignition improver.

Controlling ignition delay is the key to successfully enable partially premixed combustion in diesel engines. This paper presents experimental results of partially premixed combustion in an optically accessible engine, using primary reference fuels in combination with artificial exhaust gas recirculation. By changing the fuel composition and oxygen concentration, the ignition delay is changed. To determine the position of the flame front, high-speed visualization of OH-chemiluminescence is used, enabling a cycle-resolved analysis of OH formation. A clear correlation is observed between ignition delay and flame location. The mixing of fuel and air during the ignition delay period defines the local equivalence ratio, which is estimated based on a spherical combustion volume for each spray. The corresponding emission measurements using fast-response analyzers of CO, HC and NOX confirm the decrease in local equivalence ratio as a function of ignition delay.

In recent years the automotive industry has been forced to reduce the harmful and pollutant emissions emitted by direct-injected diesel engines. To accomplish this difficult task various solutions have been proposed. One of these proposed solutions is the usage of gaseous fuels in addition to the use of liquid diesel. These gaseous fuels have more gasoline-like properties, such as high octane numbers, and thereby are resistant against auto-ignition. Diesel on the other hand, has a high cetane number which makes it prone to auto-ignition. In this case the gaseous fuel is injected in the inlet manifold, and the diesel is direct injected in the cylinder at the end of the compression stroke. Thereby the diesel fuel spontaneously ignites and acts as an ignition source. The main goals for the use of a dual-fuel operation with diesel and gaseous fuels are the reduction of particulate matter (PM) and nitrogen oxides (NOx) emission.

Recently, some studies have shown high efficiencies using controlled auto-ignition by blending gasoline and diesel to a desired reactivity. This concept has been shown to give high efficiency and, because of the largely premixed charge, low emission levels. The origin of this high efficiency, however, has only partly been explained. Part of it was attributed to a lower temperature combustion, originating in lower heat losses. Another part of the gain was attributed to a faster, more Otto-like (i.e. constant volume) combustion. Since the concept was mainly demonstrated on one single test setup so far, an experimental study has been performed to reproduce these results and gain more insight into their origin. Therefore one cylinder of a heavy duty test engine has been equipped with an intake port gasoline injection system, primarily to investigate the effects of the balance between the two fuels, and the timing of the diesel injection.