Methane Diesel Research Articles

Retrofit of a Marine Engine to Dual-Fuel Methane–Diesel: Experimental Analysis of Performance and Exhaust Emission with Continuous and Phased Methane Injection Systems

Shipping is a highly energy-intensive sector, and fleet decarbonization initiatives can significantly reduce greenhouse gas emissions. In the short-to-medium term, internal combustion engines will continue to be used for propulsion or as electricity generators onboard ships. Natural gas is an effective solution which can be used to mitigate greenhouse gas emissions from the marine sector. Considered to be a transitional fuel, it can provide a potential reduction in CO2 emissions of around 20–30%, compared with conventional marine fuels. This work investigated the influence of diesel-injection strategies on the performance and emissions of a single-cylinder prototype compression-ignition engine for marine applications, retrofitted to run as a Low-Pressure Dual-Fuel Engine using natural gas. Two different injection systems were used: a mass flow controller enabling continuous-mode gas feeding, and a Solenoid-Operated Gas Admission Valve for marine applications, the latter allowing phased natural-gas injection. Experimental tests were focused on partial-load conditions, which are critical for dual-fuel engines, with a natural gas/diesel mass ratio of 4:1. Phased injection resulted in reductions in fuel consumption, compared to continuous mode, of up to 11%. Further experiments demonstrated reductions in fuel consumption of up to 20.7% (in equivalent diesel); on the other hand, the unburned hydrocarbon emissions which resulted were an order of magnitude larger than the reference values for full diesel, reducing the benefits in terms of greenhouse gas emissions, with a reduction in Global Warming Potential of only 3% compared to full diesel.

Methane slip reduction of conventional dual-fuel natural gas diesel engine using direct fuel injection management and alternative combustion modes

Alternative combustion mode and change of spray geometry show potential for methane slip reduction in a dual fuel diesel-natural gas internal combustion engine. Three combustion regimes are simulated; a conventional diesel methane dual-fuel combustion and two modes of reactivity controlled compression ignition (RCCI) with early (EIRCCI) and late (LIRCCI) injections. Methane is injected as the premixed fuel into the port and diesel as direct-injected fuel in all combustion modes. The start of direct fuel injection (SOI) is used as the combustion management tool, swiping from misfiring to knock limits at part loads.By switching combustion mode from conventional (CDF) to LIRCCI and EIRCCI, methane slip is reduced by 12% and 33%, respectively. SOI is used effectively to manage methane slip in any combustion mode, but the effect is more substantial in the EIRCCI mode.Emission results support methane slip trends’ observations. Nitrogen oxides (NOx) emission is increased in CDF by advancing SOI and decreased in both the LIRCCI and EIRCCI modes. Compared to CDF, late and early injection RCCI modes produce 417% and 67% more soot. Also, results show that high levels of methane slip in CDF can be reduced to some extent without any geometry modification by SOI management.Three diesel spray angles (SAs) of 60, 90, 120° are examined. Minimum methane slip is obtained when the SA is towards the squish area, and maximum methane slip is obtained when the SA is towards the piston bowl. Increasing SA from 60 to 90 and 120° results in a 16.4% and 42.5% reduction of methane slip.

Numerical investigation on combustion and emissions in a direct injection compression ignition engine fuelled with various hydrogen–methane–diesel blends at different intake air temperatures

Blending hydrogen and methane with diesel in compression ignition engines has been proven to improve both performance and emissions. This work further explores the combustion characteristics and emissions of a direct injection compression ignition (DICI) engine fuelled with various blend ratios of hydrogen, methane and diesel with respect to varying intake air temperatures, as the blend ratio can affect the mixture formation process in such high-speed in-cylinder phenomena. A numerical study using ANSYS Fluent was conducted based on a 0.406-litre Yanmar L100AE-D single-cylinder DICI engine running at 1500 rpm and was verified with a physical experiment using the same engine. The tri-fuel blend consisted of 60% diesel by mass with the remaining 40% made up with various ratios of hydrogen and methane (0%/40%, 12%/28%, 20%/20%, 28%/12%, and 40%/0%). The intake air temperatures were varied at 303 K, 318 K and 338 K, representing near-standard, high and extremely high ambient air temperatures, respectively. The results showed that the presence of methane and hydrogen in diesel fuel resulted in a higher in-cylinder pressure, temperature and heat release rate (HRR). Increasing the intake air temperature caused a proportional increase in the in-cylinder temperature, pressure and HRR. However, the presence of methane lengthened the ignition delay, while increasing hydrogen reversed the trend. While the presence of hydrogen–methane reduced the overall CO emissions, the effect of hydrogen on CO reduction was dominant. In addition, the presence of hydrogen–methane led to an increase in NOx emissions due to the high combustion temperature. The study suggested that an optimized intake temperature and the balanced use of tri-fuel in a direct injection compression ignition engine can significantly improve engine performance and emissions.

Impact of low reactivity fuel type on low load combustion, emissions, and cyclic variations of diesel-ignited dual fuel combustion

In this study, cyclic variations in dual fuel combustion with diesel ignition of three different low reactivity fuels (methane, propane, and gasoline) are examined under identical operating conditions. Experiments were performed on a single cylinder research engine (SCRE) at a low load of 3.3 bar brake mean effective pressure (BMEP). The start of injection (SOI) of diesel was varied from 280 to 330 absolute crank angle degrees (CAD). Engine speed, rail pressure, and boost pressure were held constant at 1500 rpm, 500 bar, and 1.5 bar, respectively. The energy substituted by the low reactivity fuel was fixed at 80% of the total energy input. It was found that diesel-methane (DM) and diesel-propane (DP) combustion were affected by diesel mixing to a greater extent than diesel-gasoline (DG) combustion due to the higher reactivity of gasoline. The magnitude of low temperature heat release was greatest for DG combustion followed by DM and DP combustion for all SOIs. The ignition delay for DG combustion was the shortest, followed by DM and DP combustion. DM and DP combustion exhibited more cyclic variations than DG combustion. Cyclic variations decreased for DM and DP combustion when SOI was advanced; however, DG combustion cyclic variations remained essentially constant for all SOIs. Earlier SOIs (280, 290, 300, and 310 CAD) for DM and (280, 290, and 300 CAD) for DP combustion indicated some prior-cycle effects on the combustion and IMEP (i.e. some level of determinism).

Large-eddy simulation of tri-fuel ignition: diesel spray-assisted ignition of lean hydrogen–methane–air mixtures

We present 3D numerical results on tri-fuel (TF) combustion using large-eddy simulation and finite rate chemistry. The TF concept was recently introduced by Karimkashi et al. (Int. J. Hydrogen Energy, 2020) in 0D. Here, the focus is on spray-assisted ignition of methane–hydrogen blends. The spray acts as a high-reactivity fuel (HRF) while the ambient premixed methane-hydrogen blend acts as a low-reactivity fuel (LRF) mixture. Better understanding on such a TF process could enable and motivate more extensive hydrogen usage in e.g. compression ignition marine engines where spray-assisted dual-fuel (DF) combustion is already utilised. The studied spray set-up is based on the modified ECN Spray A case, see Kahila et al. (Combustion and Flame, 2019) for DF combustion. The ambient pressure and temperature are 900 K and 60 bar. The hydrogen content of the LRF blend is varied systematically by changing the molar fraction , . The main added value of the study is that we extend the TF concept to 3D. The particular findings of the study are as follows: 1) Consistent with Karimkashi et al. 2020, hydrogen delays ignition also in 3D and the effect becomes significant for . 2) The ratio between the first- and second-stage ignition delay times and . Furthermore, the ratio between 3D and 0D ignition delay times is given as for all TF cases. 3) Finally, consistent with Karimkashi et al. 2020, also in 3D the high-temperature combustion heat release mode is shown to appear stronger in TF than the low-temperature combustion mode compared to DF methane–diesel combustion.

A Computational Investigation of the Impact of Multiple Injection Strategies on Combustion Efficiency in Diesel–Natural Gas Dual-Fuel Low-Temperature Combustion Engines

AbstractDual-fuel diesel–methane low-temperature combustion (LTC) has been investigated by various research groups, showing high potential for emissions reduction (especially oxides of nitrogen oxide (NOx) and particulate matter (PM)) without adversely affecting fuel conversion efficiency in comparison with conventional diesel combustion. However, when operated at low load conditions, dual-fuel LTC typically exhibits poor combustion efficiencies. This behavior is mainly due to low bulk gas temperatures under lean conditions, resulting in unacceptably high carbon monoxide (CO) and unburned hydrocarbon (UHC) emissions. A feasible and rather innovative solution may be to split the pilot injection of liquid fuel into two injection pulses, with the second pilot injection supporting CO and UHC oxidation once combustion is initiated by the first one. In this study, diesel–methane dual-fuel LTC is investigated numerically in a single-cylinder heavy-duty engine operating at 5 bar brake mean effective pressure (BMEP) at 85% and 75% percentage of energy substitution (PES) by methane (taken as a natural gas (NG) surrogate). A multidimensional model is first validated in comparison with the experimental data obtained on the same single-cylinder engine for early single pilot diesel injection at 310 crank angle degrees (CAD) and 500 bar rail pressure. With the single pilot injection case as baseline, the effects of multiple pilot injections and different rail pressures on combustion and emissions are investigated, again showing good agreement with the experimental data. Apparent heat release rate and cylinder pressure histories as well as combustion efficiency trends are correctly captured by the numerical model. Results prove that higher rail pressures yield reductions of HC and CO by 90% and 75%, respectively, at the expense of NOx emissions, which increase by ∼30% from baseline still remaining at very low level (under 1 g/kWh). Furthermore, it is shown that postinjection during the expansion stroke does not support the stable development of the combustion front as the combustion process is confined close to the diesel spray core.

1D Simulation and Experimental Analysis on the Effects of the Injection Parameters in Methane–Diesel Dual-Fuel Combustion

Notwithstanding the policies that move towards electrified powertrains, the transportation sector mainly employs internal combustion engines as the primary propulsion system. In this regard, for medium- to heavy-duty applications, as well as for on- and off-road applications, diesel engines are preferred because of the better efficiency, lower CO2, and greater robustness compared to spark-ignition engines. Due to its use at a large scale, the internal combustion engines as a source of energy depletion and pollutant emissions must further improved. In this sense, the adoption of alternative combustion concepts using cleaner fuels than diesel (e.g., natural gas, ethanol and methanol) presents a viable solution for improving the efficiency and emissions of the future powertrains. Particularly, the methane–diesel dual-fuel concept represents a possible solution for compression ignition engines because the use of the low-carbon methane fuel, a main constituent of natural gas, as primary fuel significantly reduces the CO2 emissions compared to conventional liquid fuels. Nonetheless, other issues concerning higher total hydrocarbon (THC) and CO emissions, mainly at low load conditions, are found. To minimize this issue, this research paper evaluates, through a new and alternative approach, the effects of different engine control parameters, such as rail pressure, pilot quantity, start of injection and premixed ratio in terms of efficiency and emissions, and compared to the conventional diesel combustion mode. Indeed, for a deeper understanding of the results, a 1-Dimensional spray model is used to model the air-fuel mixing phenomenon in response to the variations of the calibration parameters that condition the subsequent dual-fuel combustion evolution. Specific variation settings, in terms of premixed ratio, injection pressure, pilot quantity and combustion phasing are proposed for further efficiency improvements.

Chemical/Physical Features of Particles Emitted from a Modern Automotive Dual-Fuel Methane–Diesel Engine

The dual-fuel (DF) diesel–natural gas (NG) combustion concept for automotive engine applications has received increased attention in the recent years. The reasons of such interest lie in the need to identify energy sources alternative to fossil oil fuels, valid and competitive from an environmental point of view. Gaseous fuels, such as NG and methane, are very promising and highly attractive to this aim because of their easy availability, widespread distribution infrastructure, low cost, and clean-burning qualities. With respect to conventional diesel fuel, in fact, NG and methane permit a significant reduction of CO2 and are less prone to soot formation. Notwithstanding that the significant soot reduction offered by the DF engine combustion mode is a consolidated result, the compliance with future stringent regulations on engine particulate emissions will still require the adoption of after-treatment devices, such as the diesel particulate filter (DPF). Therefore, a complete characterization of the parti...

Numerical study of combustion characteristics and emissions of a diesel–methane dual-fuel engine for a wide range of injection timings

Computational fluid dynamics simulations are performed to investigate the combustion and emission characteristics of a diesel/natural gas dual-fuel engine. The computational fluid dynamics model is validated against experimental measurements of cylinder pressure, heat release rate, and exhaust emissions from a single-cylinder research engine. The model predictions of in-cylinder diesel spray distribution and location of diesel ignition sites are related to the behavior observed in measured and predicted heat release rate and emissions. Various distributions of diesel fuel inside the combustion chamber are obtained by modifying the diesel injection timing and the spray included angle. Model predictions suggest that the distribution of diesel fuel in the combustion chamber has a significant impact on the characteristics of heat release rate, explaining experimental observations. Regimes of combustion in the dual-fuel engine are identified. Turbulent flame speed calculations, premixed turbulent combustion regime diagram analysis, and high-temperature front propagation speed estimation indicated that the dual-fuel combustion in this engine was supported by successive local auto-ignition and not by turbulent flame propagation.

Investigation of the effects of biogas composition on the performance of a biogas–diesel dual fuel CI engine

ABSTRACTIn this study, biogas is used in a CI engine in dual fuel mode with diesel as pilot fuel. Biogas has been replicated using a mixture of methane (CH4) and carbon dioxide (CO2), whose flow rates can be independently varied. This helps in evaluating the effect of biogas composition on engine performance. Apart from the conventional diesel-only mode, the engine is operated in dual fuel mode with induction of (a) pure CH4 and (b) CH4 + CO2 mixtures with variable CH4:CO2 ratios, representing biogas. Dual fuel operation is observed to have better brake thermal efficiencies compared to diesel-only mode at high loads. Though volumetric efficiency is almost identical in diesel-only and diesel–CH4 dual modes, induction of biogas causes it to drop. Exhaust gas temperatures were higher in diesel–biogas mode, followed by diesel–methane and diesel-only modes. Dual fuel mode, especially with biogas, results in higher overall equivalence ratios. Compared to diesel-only mode, dual fuel mode has relatively high unaccounted losses at low loads, while exhaust and coolant losses are greater at high loads. Biogas composition does not significantly affect any of the above parameters except the exhaust gas temperature and air–fuel ratio, which show a slight increase with methane enrichment.

Injection timing effects on partially premixed diesel–methane dual fuel low temperature combustion

Dual fuel low temperature combustion (LTC) strategies are attractive for future internal combustion engines due to their promise of very low engine-out emissions of oxides of nitrogen (NOx) and particulate matter. In the present work, experimental results for diesel-ignited methane dual fuel LTC on a compression ignition single cylinder research engine (SCRE) are presented. Methane was fumigated into the intake manifold and diesel injection was used to initiate combustion. The engine was operated at a constant speed of 1500rev/min, and diesel injection pressure was fixed at 500bar. The start of injection (SOI) of diesel fuel was varied from 260° to 360° (i.e., TDC) to quantify its impact on engine performance and engine-out, indicated-specific emissions of NOx (ISNOx), carbon monoxide (ISCO), and unburned hydrocarbons (ISHC), and smoke emissions. The SOI sweeps were performed at different net indicated mean effective pressures (IMEPs) of 4.1 and 12.1bar. Intake manifold pressure and methane percent energy substitution (PES) were fixed at 1.5bar and 80%, respectively, for 4.1bar IMEP and at 1.8bar and 95%, respectively, for 12.1bar IMEP. For all loads, when SOI was advanced, the longer ignition delays caused the separation between the fuel injection and the combustion events to increase. This was accompanied by a change in the shape of the AHRR curve from a distinct two-stage profile to a smooth, single-stage (almost Gaussian) profile. Advancing SOI to 300° and beyond yielded minimal engine-out ISNOx emissions (∼0.15g/kWh at 4.1bar IMEP and ∼1.3–1.5g/kWh at 12.1bar IMEP). Smoke emissions were negligible (<0.05 FSN) for all loads and all SOIs. Very high ISHC and ISCO emissions were observed for near-TDC SOI at all loads. The lowest ISHC and ISCO levels occurred for SOIs near 310° and for more advanced SOIs, both emissions increased. High pressure rise rates and the tendency to knock prevented engine operation at intermediate SOIs between 310° and 340° for 12.1bar IMEP. On the other hand, for both 4.1bar and 12. 1bar IMEPs, high coefficient of variation of IMEP (>5%) caused unstable engine operation for SOIs advanced beyond 280°.

Detailed characterization of diesel-ignited propane and methane dual-fuel combustion in a turbocharged direct-injection diesel engine

This paper presents an experimental analysis of dual-fuel combustion based on the performance, emissions, and in-cylinder combustion measurements with gaseous propane or gaseous methane as the primary fuel and diesel as the pilot fuel. Two different sets of experiments were performed on a 1.9 litre four-cylinder engine at a constant engine speed of 1800 r/min: first, constant-pilot-quantity experiments, allowing the primary fuel concentration and the brake mean effective pressure to vary; second, constant-brake-mean-effective-pressure experiments, allowing the percentage energy substitution of the primary fuel and the pilot quantity to vary. In the constant-pilot-quantity experiments, the apparent heat release rate profiles showed the influence of the preignition chemistry and gaseous fuel burn rates on the dual-fuel combustion phasing and duration, the fuel conversion efficiency, and the engine-out emissions. With a fixed pilot quantity, the nitrogen oxide emissions were either reduced or unaffected while the smoke levels were increased or unaffected with increasing primary fuel concentration. The carbon monoxide and total unburned hydrocarbon emissions decreased and the fuel conversion efficiency increased as the pilot quantity or the primary fuel concentration was increased. Overall, diesel–propane combustion yielded higher carbon monoxide emissions, lower total unburned hydrocarbon emissions, and slightly higher fuel conversion efficiencies than diesel–methane combustion did. In the constant-brake-mean-effective-pressure experiments, at a brake mean effective pressure of 2.5 bar, diesel–propane and diesel–methane combustion behaved very similarly, the primary differences being in the preignition chemistry and the ignition delay trends. At a brake mean effective pressure of 2.5 bar, the nitrogen oxide and smoke emissions were simultaneously reduced while the carbon monoxide and total unburned hydrocarbon emissions were increased. At a brake mean effective pressure of 10 bar (a baseline diesel fuel conversion efficiency of 38%), diesel–propane fueling was prone to rapid earlier combustion while diesel–methane combustion was slower. For diesel–methane combustion at a brake mean effective pressure of 10 bar, the fuel conversion efficiency decreased to 37.1% as the percentage energy substitution was increased to 51%. For diesel–propane combustion at a brake mean effective pressure of 10 bar, the fuel conversion efficiency increased to 39% as the percentage energy substitution was increased to 46%. At high-brake-mean-effective-pressure–high-percentage-energy-substitution and large-pilot-quantity–high-equivalence-ratio conditions, diesel–propane combustion showed an apparent departure from the classical three-phase dual-fuel combustion to a distributed volumetric combustion process that resembled a “diesel-regulated homogenous-charge-compression-ignition-like” combustion process.

Combustion and emissions control in diesel–methane dual fuel engines: The effects of methane supply method combined with variable in-cylinder charge bulk motion

In this paper, the results of an extensive experimental campaign about dual fuel combustion development and the related pollutant emissions are reported, paying particular attention to the effect of both the in-cylinder charge bulk motion and methane supply method. A diesel common rail research engine was converted to operate in dual fuel mode and, by activating/deactivating the two different inlet valves of the engine (i.e. swirl and tumble), three different bulk flow structures of the charge were induced inside the cylinder. A methane port injection method was proposed, in which the gaseous fuel was injected into the inlet duct very close to the intake valves, in order to obtain a stratified-like air–fuel mixture up to the end of the compression stroke. For comparison purposes, a homogeneous-like air–fuel mixture was obtained injecting methane more upstream the intake line. Combining the different positions of the methane injector and the three possible bulk flow structures, seven different engine inlet setup were tested. In this way, it was possible to evaluate the effects on dual fuel combustion due to the interaction between methane injector position and charge bulk motion. In addition, methane injection pressure and diesel pilot injection parameters were varied setting the engine at two operating conditions. For some interesting low load tests, the combustion development was studied more in detail by means of direct observation of the process, using an in-cylinder endoscope and a digital CCD camera. Each combustion image was post-processed by a dedicated software, in order to extract only those portions with flame presence and to calculate an average luminance value over the whole frame. These luminance values, chosen as indicators of the combustion intensity, were represented over crank angle position and, then, an analysis of the resulting curves was performed. Results showed that the charge bulk motion associated to the swirl port, improving the charge mixing of the diesel spray and the propagation of the turbulent flame fronts, is capable to enhance the oxidation of air–methane mixture, both at low and high engine loads. Furthermore, at low loads, the analysis of combustion images and luminance curves showed that methane port injection can significantly affect the intensity and the spreading of the flame during dual fuel combustion, especially when a suitable in-cylinder bulk motion is obtained. Concerning the engine emissions, some correlations with what observed during the analysis of the combustion development were found. Furthermore, it was revealed that, for several combinations of the engine operating parameters, methane port injection was always associated to the lowest emission levels, demonstrating that this methane supply method is a very effective strategy to reduce unburned hydrocarbons and nitric oxides concentrations, especially when implemented with variable intake geometry systems.