Low Engine Load Research Articles

Physical Characteristics of Particle Emissions from a Medium Speed Ship Engine Fueled with Natural Gas and Low-Sulfur Liquid Fuels.

Particle emissions from marine traffic affect significantly air quality in coastal areas and the climate. The particle emissions were studied from a 1.4 MW marine engine operating on low-sulfur fuels natural gas (NG; dual-fuel with diesel pilot), marine gas oil (MGO) and marine diesel oil (MDO). The emitted particles were characterized with respect to particle number (PN) emission factors, PN size distribution down to nanometer scale (1.2-414 nm), volatility, electric charge, morphology, and elemental composition. The size distribution of fresh exhaust particles was bimodal for all the fuels, the nucleation mode highly dominating the soot mode. Total PN emission factors were 2.7 × 1015-7.1 × 1015 #/kWh, the emission being the lowest with NG and the highest with MDO. Liquid fuel combustion generated 4-12 times higher soot mode particle emissions than the NG combustion, and the harbor-area-typical lower engine load (40%) caused higher total PN emissions than the higher load (85%). Nonvolatile particles consisted of nanosized fuel, and spherical lubricating oil core mode particles contained, e.g., calcium as well as agglomerated soot mode particles. Our results indicate the PN emissions from marine engines may remain relatively high regardless of fuel sulfur limits, mostly due to the nanosized particle emissions.

Development of Kuala Lumpur driving cycle for the estimation of fuel consumption and vehicular emission

Driving cycles is a series of data points representing the speed of vehicle verses time sequence profile developed for certain road, route, specific area or city. Generally, driving cycle is used to estimate the fuel consumption (FC) and vehicular exhaust emission. The common factors that affected the FC and exhaust emission are the engine operating conditions such as cold start, low engine loads and high engine loads which are found during actual driving. The research presents the measurement and analysis of engine conditions based on actual driving behaviours in an attempt to formulate representative driving cycle for Kuala Lumpur. The methodology used for this research is adapted from the Worldwide Harmonized Light-duty Test Cycle (WLTC) introduced by the working party on pollution and energy (GRPE) under the United Nations Economic Commission for Europe (UNECE). This research covered a wide area of paved road in Kuala Lumpur, about 62.34% by surveying the road condition on the eight selected routes. The used of On-board Diagnostic (OBD) and Global Positioning System (GPS) equipment are used to record the vehicle travel speed during data collection activity. The driving characteristics are then analysed from speed profile and its target statistic parameters are defined to develop representative driving cycle. The characteristics of the newly developed driving cycle are compared to the European driving cycle which is currently being used in Malaysia for new vehicle certification and registration. Therefore, the correlation of FC is derived to indicate the impacts of real-world driving conditions relative to domestic conditions.

Performance and emission analysis of a diesel engine using hydrogen enriched n-butanol, diethyl ester and Spirulina microalgae biodiesel

Comparative assessment of hydrogen added diesel, Spirulina microalgae, n-butanol and diethyl ester fuels was done to evaluate the effects of the fuel blends on the performance and exhaust emissions of a diesel engine. The impact of hydrogen energy share (5, 10, 15 and 20%) on the diesel engine at low (25%), medium (50%) and high (100%) engine loads with a constant injection timing, speed of 1500 rpm and a higher fuel injection pressure of 220 bar was analysed. The addition of hydrogen energy to the fuels increased the brake thermal efficiency (BTE) and also showed a decrease in the fuel consumption for all engine loads. Hydrogen energy addition, cylinder pressure and NOX increased at high loads. CO2 and smoke emissions were reduced with hydrogen as an additional fuel at all engine loads. The results showed that with the addition of hydrogen (15%), NOX emission increased by 21.3%, BSN emission decreased by 22.89%, specific fuel consumption decreased by 18.3% and BTE improved by 0.95% at higher engine loads. Moreover, with the addition of hydrogen energy, increases in PM, NOX, and the summary of emission were observed.

Investigation of the effects of split-injection on particle emissions from a Dieseline CI engine

Premixed compression ignition (PCI) combustion techniques utilising low cetane-number (<40) fuels are associated with low engine-out oxides of nitrogen (NOx) and soot emissions. However, fuel-air over-mixing and high combustion noise at low and high engine loads, respectively, have been the challenges with PCI. Fuel split-injection can effectively govern the fuel-air mixing process and subsequently control combustion and emissions characteristics; it is of interest to characterise particle emissions under these PCI conditions. In this study, the effects of double-injection of low-cetane G75-Dieseline (75% gasoline in diesel based on volume) on controlling charge premixing and consequently size distribution of particle emissions were investigated in a production light-duty 4-cylinder CI engine. First injection-quantity ratio was varied from 10% to 50% while using different injection timings at engine loads from 1.4 to 12 bar BMEP and speed of 1800 RPM. Brake specific emissions results were compared to diesel baselines to quantify particles concentration reduction while maintaining the same range of NOx and brake thermal efficiency (BTE). G75 combustion emitted lower number and mass of particles (in all size classes) by up to 99.9% and generally lower NOx by up to 65% compared to diesel. Negligible particle number and mass emissions (as low as 1.91 × 1012 parts/kWh and 138 µg/kWh respectively) were measured for G75 at low-medium loads (3–6 bar BMEP). In the absence of two-stage combustion, the timing of second-injection controlled the combustion-phasing effectively. Lower first injection-quantity ratios (e.g. 10%) are recommended for overall high BTE and low gaseous and particle emissions.

Impact of methanol alternative fuel on oxidation reactivity of soot emissions from a modern CI engine

This paper compared the soot reactivity and its primarily related factors including soot structure, graphitization degree and surface functional groups, when using mineral diesel fuel (DF) and methanol blended fuel (MBF) at two typical low and high engine loads. Results showed that the soot reactivity increases with increasing methanol concentration in the MBF. Additionally, with the constant methanol blend ratio of methanol, the reactivity of MBF soot degrades as the engine load increases. Correspondingly, the MBF soots had lower aggregate compactness, smaller primary particle size, more disordered structure and more active aliphatic C-H groups in comparison with the DF soot, providing higher concentration and accessibility of active sites for oxidation reactions. The addition of methanol creates variations in combustion kinetics and fuel formulation, which exerts reverse effects on the soot structure and chemistry. Therefore, the factors related to these properties show non-monotonic variations when alter the methanol blend ratio and engine operating mode. Especially, when the methanol blend ratio increases from 10% to 15%, the soot structure and chemistry transform onto the features that are reluctant for soot oxidation.

Impact of spray-wall interaction on the in-cylinder spatial unburned hydrocarbon distribution of a gasoline partially premixed combustion engine

Partially premixed combustion (PPC) often adopts the early fuel-injection strategy that could result in spray-wall interaction involved with piston top-land crevice. This interaction may produce a significant impact on engine combustion and unburned hydrocarbons (UHC) emission, which is still not well understood. In this study, we investigated the detailed spray-wall interaction and its effects on the two-stage ignition, i.e. low- and high-temperature heat release (LTHR and HTHR), and the in-cylinder spatial UHC distribution of PPC in a full-view optical engine at low engine load. The PRF 70 fuel was used as the gasoline surrogate. The high-speed imaging of the natural flame luminosity was acquired to quantify the flame probability distribution. The qualitative fuel-tracer, formaldehyde, and UHC planar laser-induced fluorescence (PLIF) imaging techniques were employed to reveal the fuel, LTHR and UHC distribution characteristics, respectively. The LTHR, HTHR and UHC distribution formed by the fuel trapped in the piston top-land crevice were visualized by PLIF imaging techniques for the first time. The PLIF results indicate that the main UHC formed in the PPC engine comes from the central part of the cylinder close to the injector nozzle, where the overall equivalence ratio is low and the injector dribbling is an important source of UHC. The UHC formed in the piston crevice of the PPC engine depends on the local equivalence ratio of the fuel trapped in the crevice. When the overall equivalence ratio of the charge in the crevice is relatively high, the trapped fuel undergoes both LTHR and HTHR and produces negligible UHC. However, the UHC from the piston crevice becomes considerable when the fuel injection timing is too early so that an overly lean mixture is generated. Based on the above findings, three implications of the PPC operation at low engine load for low UHC emission and high engine efficiency are proposed.

Impact of post-injection strategies on combustion and unregulated emissions during different loads in an HSDI diesel engine

This research was done to study combustion and emissions characteristics especially unregulated emissions from a heavy-duty diesel engine based on three engine loads (20%, 40%, 60%) with different post-injection (PI) strategies, at six start of injection timings (SOI) with a 20° crank angle (CA) interval (20–120 °CA) and three post-injection fuel masses (PIM) (5 mg, 10 mg and 15 mg) at constant speed of 1200 revolution per minute (rpm). Common regulated (NOx, soot, and THC) and un-regulated emissions including carbonyl compounds (acetaldehyde, formaldehyde), saturated (methane, ethane, propane) and unsaturated (ethylene, propylene, 1,3 butadiene) emissions were recorded with Fourier Transform Infrared analyzer (FTIR). An early post-injection can increase the engine power output and raise the temperature of the exhaust gases at all engine loads. Reduction in NOx up to 25% and THC up to 60% were recorded at 60°CA while up to 80% reduction in soot emissions was recorded at SOI 80-120°CA with PI strategies at medium to high loads. For all the P.I strategies results indicated that unregulated emissions increased with the increase in the PIM and mostly the peak values of unregulated emissions recorded at SOI 60–80 °CA with 15 mg PIM. Post-injection at 60-80 °CA found most suitable to produce light hydrocarbon (HC) at lower engine load. In general, the post-injection reduced regulated/unregulated emissions and generate light HC relative to the single main injection which is beneficial for after-treatment devices.

Effects of the three dual-fuel strategies on performance and emissions of a biodiesel engine

Three dual-fuel strategies, i.e. Strategy S (syngas-biodiesel), Strategy U (upgraded syngas-biodiesel), and Strategy D (DME-biodiesel), for utilization of syngas and biodiesel from biomass wastes in internal combustion engines have been proposed in this study. To compare both the combustion and emission performance of the three strategies, an integrated KIVA4-CHEMKIN CFD platform was constructed implementing a newly combined reaction mechanism. Effects of three dual-fuel strategies have been compared against each other in terms of indicated power, NOx and soot emission. At different engine loads, it was found that the indicated power of all strategies increased with the increasing supplement ratio. Strategy S and Strategy U predict higher indicated power than Strategy D at the high engine load, while lower indicated power than Strategy D at the low engine load. As regards to the NOx emission, an increase in the fuel supplement ratio increases the NOx emission (g/kWh) for both Strategy S and Strategy U at high engine loads, while decreases the NOx emission (g/kWh) due to the enhanced indicated power. Strategy D has relatively higher NOx emission (g/kWh) than Strategy S and Strategy U at all loads. With the increase in fuel supplement ratio, the soot emission generally shows a decreasing trend at all engine loads for all strategies, and Strategy D emits less soot than Strategy S and Strategy U in the cases of high fuel supplement ratio (>0.4) for all engine load conditions.

Potential of using OMEx as substitute of diesel in the dual-fuel combustion mode to reduce the global CO2 emissions

To achieve the targets of extreme low emissions values for the transport sector, several technologies emerged in the last few years. In this sense, advanced combustion modes as the dual-fuel low temperature combustion showed great advantages in terms of NOx and soot emissions reduction. At low and medium engine load, the operation is stable with virtually zero emissions. However, the exhaust gas recirculation rates at high load need to be increased to avoid excessive in-cylinder peaks, which leads to higher soot emissions. At these conditions, the use of non-sooting fuels as the oxymethylene dimethyl ethers (OMEx) allows avoiding the NOx-soot trade-off. In addition, the e-fuel consideration of the OMEx makes it suitable to reduce the global GHG emissions. This paper assesses the potential of using OMEx as high reactivity fuel to reduce the CO2 well-to-wheel emissions, and NOx and soot tailpipe emissions, in a medium-duty truck operating under dual-fuel combustion in transient conditions. The cargo mass was varied between 0% and 100% (18 ton) in the World Harmonized Vehicle Cycle. The tank-to-wheel analysis shows slightly higher CO2 production with OMEx-gasoline than with diesel-gasoline due to the ratio between the lower heating value and the carbon content. However, the well-to-wheel analysis shows the benefits of using OMEx to reduce the carbon dioxide footprint, which ranges from 13% (at full cargo mass) to 19% (at low cargo mass) compared to diesel-gasoline dual-fuel mode. This benefit is due to the large gains in terms of fuel production due to the carbon capture and the clean electric energy source necessary to produce the OMEx.

The contribution of CNG powered vehicles in the transition to zero emission mobility - example of the light commercial vehicles fleet

The aim of paper was to discuss contribution of bi-fuel CNG powered light commercial vehicles to the Well-To-Wheel CO2 equivalent emissions, both today and in the coming decades in which the development of new fuels and new vehicles is expected. Field research was done in Belgrade, during one year, using Euro 5 diesel/LPG/CNG light commercial vehicles driving under low vehicle speed, low engine load, low exhaust gas temperature and high number of stops. WTW as neutral methodology was applied for understanding of each fuel pathway in terms of reducing greenhouse gas emissions and increasing energy efficiency. Calculation showed that total energy consumption per km is the lowest for diesel vehicles since petrol/LPG and petrol/CNG vehicles use 21% and 7 % more energy. Tank-To-Wheel emission of CO2e is most favorable for petrol/CNG with 28.8 % and 6.7 % less CO2e with petrol/LPG and diesel vehicles. The same conclusion brings Well-To-Wheel analysis showing that diesel/CNG CO2e emission is 13.5 % less than petrol/LPG, apropos 1.5 % less than diesel operated vehicles considered within this field research. Figures are not as high as previous, due to the results of Well-To-Tank emission, that were most favorable for petrol/LPG powered vehicles, with almost 51% and 32% better results regarding to petrol/CNG and diesel, respectively. Within same time, lowest fuel cost per km was achieved by petrol/CNG vehicles, with 32% and 35% less cost than petrol/LPG and diesel vehicles. The available CNG technology should not be neglected, waiting for new solutions to be proven.

An experimental evaluation of engine performance and emissions characteristics of a modified direct injection diesel engine operated in RCCI mode

This study explored methods to evaluate the test engine characteristics operated based on the reactivity controlled compression ignition (RCCI) technology to reduce fuel consumption and exhaust emissions, especially PM and NOx. Consequently, gasoline and diesel, respectively, considered as the low reactivity fuel (LRF) and high reactivity fuel (HRF), are injected in the intake manifold and combustion chamber. The experimental procedure is conducted at a constant speed of 2000 rpm, and brake mean effective pressure (BMEP) from low load 0.84 bar to high load 4.24 bar. The injection strategy is varied according to the engine loads. Indeed, at the low and medium engine load condition, the diesel fuel is injected double injection pulse, at the high load, the diesel fuel is injected single injection pulse. The injection timing is advanced from the top dead center (TDC) until knocking happens or the coefficient of variation (COV) higher than 10%, and maximum advanced injection timing is 65 crank angle degree (℃A) before the top dead center (BTDC). The results of advanced injection timing show that limit of advanced timing in low load is COV while at high load is knocking; at medium load, the diesel injection timing can be advanced to 65℃A BTDC. The exhaust emissions of CO and HC are higher than conventional diesel engines, while soot is hugely lower in all operating points. NOx emission is much dependent on injection timing, at 10 to 20℃A BTDC NOx highest, and approximately to the conventional diesel engine, NOx reduction when injection timing advanced.

Effect of titanium dioxide nanoparticle as an additive on the exhaust characteristics of diesel-water emulsion fuel blends

The present article details the exhaust characteristics of a CI engine fueled with diesel-water emulsion fuel blends and TiO2 nanoadditive incorporated emulsion fuel blends. BD with different concentrations of water and TiO2 nanoparticle were prepared using mechanical agitation, followed by an ultra-sonication process. The physiochemical properties of test fuel were measured based on EN590 standards, and the results show a good agreement with standard limits. The experiments were carried out in a single-cylinder, four stroke, and natural aspirated diesel engine under different BMEP conditions. The emission characteristics of test fuels show that the water emulsified BDs reduce the NOx and smoke emissions. The HC and CO emissions of water emulsified BD are seem to be higher at low-engine loads, and this trend is reversed at high-engine loads. 10% water in BD reduces the EGT by 8.8% at peak BMEP condition. An inclusion of TiO2 nanoparticle significantly improves the exhaust characteristics.

Spark Assisted Compression Ignition Engine with Stratified Charge Combustion and Ozone Addition

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;Performance and emissions characteristics for stratified charge spark assisted compression ignition (SACI) with 30 ppm of added ozone (O&lt;sub&gt;3&lt;/sub&gt;) were explored in a single-cylinder, optically accessible, spray-guided, research engine. For the present study, intake pressure and temperature were fixed at 1.0 bar and 42°C respectively, with a range of engine loads (1.5 – 5.5 bar indicated mean effective pressure) and speeds (800 – 1600 revolutions per minute) explored. Fuel stratification achieved by a late-cycle injection of ~ 10–25% of the total fuel was used to maintain stable operation at lower engine loads. For each condition spark timing, second injection SOI, and fuel split ratio between the main and second injection were optimized to maximize engine performance while maintaining nitrogen oxide emissions (NOx) below 5 g/kg-fuel.&lt;/div&gt;&lt;div class="htmlview paragraph"&gt;Ozone addition was found to decrease specific fuel consumption by up to 9%, with across the board improvement in combustion stability relative to similar conditions without O&lt;sub&gt;3&lt;/sub&gt;. The effect of O&lt;sub&gt;3&lt;/sub&gt; addition was most substantial for the lowest loads. Moreover, because a higher fraction of the fuel burned was due to end-gas auto-ignition, specific NOx emissions likewise decreased by up to 30%. From complementary measurements of in-cylinder O&lt;sub&gt;3&lt;/sub&gt; decomposition acquired via an ultraviolet light absorption diagnostic, it was observed that rapid decomposition of O&lt;sub&gt;3&lt;/sub&gt; into molecular and atomic oxygen coincided with the onset of end-gas auto-ignition. The burst of resultant atomic oxygen was thought to accelerate low-temperature heat release (LTHR) reactions in the end gas. Optimal end-gas auto-ignition started between 20 and 30 crank angles before top dead center with temperatures at LTHR onset estimated to be between 575 and 700 K. An included analysis indicates that the spark deflagration was needed to add between 10 and 40 J of additional thermal energy to the end gas to achieve optimal auto-ignition.&lt;/div&gt;&lt;/div&gt;

Experimental study on engine combustion and particle size distributions fueled with Jet A-1

In this study, a comprehensive investigation of combustion and emission characteristics of Jet A-1 applied in diesel engine was experimentally conducted. Analysis is emphasized on engine performance and soot particle emission both in size and number concentrations when fueled with Jet A-1, compared with traditional diesel fuel. It is concluded that compared with diesel combustion, the combustion phase is obviously retarded when fueled with Jet A-1. The premixed combustion fraction with Jet A-1 is increased and the peak of premixed heat release of Jet A-1 is higher compared with diesel combustion under different injection pressures and different engine loads. Fuel economy with Jet A-1 is significantly improved compared with diesel, which is because of higher low heating value of Jet A-1 as well as more intensive heat release near top dead center (TDC). Jet A-1 and diesel show similar trends in particle size distribution along with the changes of engine loads. Under the low engine load, the particle size distribution is basically dominated by nucleation mode, meanwhile higher concentration of nucleation particles is observed when fueled with Jet A-1 compared to diesel. As the engine load increases, the accumulation particles are increased while the nucleation particles are in turn decreased. When the engine is running under high engine load, the particle size distribution is dominated by accumulation mode. Based on these findings, the potential to improve fuel economy and reduce particulate matter (PM) emissions by using Jet A-1 in a diesel engine was therefore proposed.

Improving pre-turbine selective catalytic reduction systems in marine two-stroke diesel engines using hybrid turbocharging: A numerical study of selective catalytic reduction operation range and system fuel efficiency

In this article, a performance evaluation of a novel system solution combining a hybrid turbocharger and a pre-turbine selective catalytic NOx reduction system is carried out. Pre-turbine selective catalytic system are used with marine two-stroke diesel engines to comply with International Maritime Organization Tier III. The system solution focuses on expanding the selective catalytic reduction operation range which is limited by fuel sulphur content by increasing exhaust temperature at low engine loads. The extended operation range is to be achieved while minimizing any fuel consumption penalties. Increasing the operation range brings improvements to emission levels during manoeuvring operations which are often carried out close to populated areas. It also provides flexibility by enabling emission reduction during slow steaming operations in which mitigating fuel consumption penalties is paramount. In addition to system evaluation in still water conditions, furthermore evaluations have been carried out taking into consideration the effect of waves on the system performance. Investigating the effect of operating in waves bring additional insight that is relevant for predicting performance in operational conditions. Analysis of the system solution found that improvements in selective catalytic reduction operation range can be achieved while also improving fuel consumption. Fuel consumption is significantly improved in the high load range. Effect of realistic operation conditions where found to affect performance; however, significant effects are only found for harsh sea states in the load range below the design point.

Evaluation of thermal barrier coatings and surface roughness in a single-cylinder light-duty diesel engine

The effect of two thermal barrier coatings and their surface roughness on heat transfer, combustion, and emissions has been investigated in a single-cylinder light-duty diesel engine. The evaluated thermal barrier coating materials were plasma-sprayed yttria-stabilized zirconia and hard anodized aluminum, which were applied on the piston top surface. The main tool for the investigation was cylinder pressure analysis of the high-pressure cycle, from which the apparent rate of heat release, indicated efficiency, and heat losses were derived. For verification of the calculated wall heat transfer, the heat flow to the piston cooling oil was measured as well. Application of thermal barrier coatings can influence engine operating conditions like charge temperature and ignition delay. Therefore, extra attention was paid to choosing stable and repeatable engine operating points. The experimental data were modeled using multiple linear regression to isolate the effects of the coatings and of the surface roughness. The results from this study show that high surface roughness leads to increased wall heat losses and a delayed combustion. However, these effects are less pronounced at lower engine loads and in the presence of soot deposits. Both thermal barrier coatings show a reduction of cycle-averaged wall heat losses, but no improvement in indicated efficiency. The surface roughness and thermal barrier coatings had a significant impact on the hydrocarbon emissions, especially for low-load engine operation, while their effect on the other exhaust emissions was relatively small.

Influence of cetane-detergent additives into diesel fuel with RME content increased to 10% on the parameters of indicator diagrams and rate of heat release in a diesel engine

This publication is the next part of the article “The influence of cetane-detergent additives in diesel fuel increased to 10% of RME content on energy parameters and exhaust gas composition of a diesel engine”. The cause-effect analysis of the phenomena related to the impact of 3 additive packages used in diesel oil with RME content increased to 10% (compare to standard diesel fuel with 7% of RME) was described. The basis for the analysis of the impact of the tested fuels on energy parameters and composition of exhaust gases were the parameters of indicator diagrams and heat release parameters. It was found that the first set of additives affects the delay of auto-ignition of fuel and kinetic fuel combustion speed only at low engine loads. In this range of engine operation the NOx concentration in the exhaust gas is low and besides there is a large of EGR.The second additive package was operated at high engine loads but its impact on the lower self-ignition delay was quantitatively small. Therefore, in the third packet of additives, the amount of additives used in the second packet was doubled. Then a satisfactory shortening of the self-ignition delay and reduction of the max rate of kinematic heat release was achieved as a reason of a reduction of NOx concentration in the exhaust up to 8% (compared to the reference fuel).

Numerical investigation on the effects of load conditions and hydrogen-air ratio on the combustion processes of a HSDI engine

Owing to high specific energy and low emissions production, hydrogen is a desirable alternative fuel. The combustion and emission performance can be improved by hydrogen addition injected in-cylinder, intake manifold and aspirated with air. However, engine loads and hydrogen-air ration have a significant effect on the performance, combustion and emission of the diesel-hydrogen (high speed direct injection) HSDI engine. In this paper, the CFD method is used to calculate the combustion process of a diesel-hydrogen dual HSDI engine working at constant speed of 4000 rpm, at different hydrogen added from intake port (hydrogen volume fraction of 0%–10%) and five engine loads (equivalent to 20%, 40%, 60%, 80% and 100% of its maximum output power), respectively. The modelling results showed that the in-cylinder pressure and temperature under low engine load were more affected by hydrogen addition. With increasing hydrogen volume fraction, the indicated expansion work and in-cylinder peak pressure increased, and combustion duration decreased due to faster fuel-air mixing and spray flame speed.

Effect of fuel injection strategy on combustion performance and NOx/smoke trade-off under a range of operating conditions for a heavy-duty DI diesel engine

The combustion process and exhaust emissions of a conventional diesel engine can be improved by manipulating the injection strategy (timing and pressure) without modification of the design. In this work, the influence of the injection strategy on the NOx emissions and smoke level was investigated experimentally for a heavy-duty diesel engine operated using diesel fuel. Different injection timings and pressures were applied to produce a variety of engine-out emission levels over different engine operating conditions. The experimental results revealed that retarding the fuel injection timing enhanced the fuel economy by reducing the brake-specific fuel consumption (BSFC). In addition, the NOx emissions were also reduced by retarding the injection timing at different engine speeds and loads. For the tested operating conditions, the NOx emissions and BSFC were lower at low engine speed and high engine load, in particular at 1200 rpm and full load (100%), respectively. The results of the experimental work indicated that the brake thermal efficiency (BTE) increased with retarded injection timings at various engine speeds. Also, the BTE was higher at low engine speed (1800 rpm) and for different injection timings. Besides, the smoke level was improved for retarded injection timing and low engine speed. Lower exhaust smoke opacity was obtained at high injection pressure compared with low injection pressure for different engine test conditions. Use of the control engine operating conditions and high injection pressure enhanced the exhaust gas temperature and BSFC, but slightly increased the NOx emissions.

Natural gas-diesel reactivity controlled compression ignition with negative valve overlap and in-cylinder fuel reforming

Dual-fuel reactivity controlled compression ignition combustion offers potentially superior overall efficiency and ultra-low nitrogen oxides and soot emissions. Using natural gas as the low reactivity fuel also provides high knock-resistance and carbon dioxide emission reduction. However, the concept suffers from relatively low combustion efficiency at low engine loads, causing unacceptable methane slip. This study tackles this issue, applying numerical simulations to investigate the application of negative valve overlap to improve combustion efficiency of reactivity controlled compression ignition at low engine loads. The objective is modification of in-cylinder thermal and chemical state before combustion, by varying timing and amount of fuel injected directly into the recompressed hot exhaust gases. The study uses TNO's multi-zone, chemical kinetics-based combustion model with variable valve actuation functionality. The simulation is based on two experimentally validated cases: an uncooled exhaust gas recirculation strategy and a lean burn concept. In both cases, negative valve overlap elevates in-cylinder temperature and cuts methane emissions by 15%, without combustion optimization. Crucially, it enables peak exhaust recompression temperatures above 850 K, sufficient for diesel reforming/oxidation. The lean RCCI strategy takes greater advantage of fuel reforming than the exhaust gas recirculation case. Optimum conditions give almost 99% combustion efficiency and ultra-low methane emissions. Net indicated efficiency is 40.5% (@15% load), despite negative valve overlap’s substantial pumping losses. Low-load net efficiency is 5.5 percentage points above the lean strategy baseline and 3 pp. better than the exhaust gas recirculation baseline. This strategy is considered applicable on state-of-the-art dual-fuel gas engines without hardware changes.