This study shows how flame development of hydrogen-diesel dual direct injection combustion is influenced by changes in two key parameters: hydrogen injection timing and hydrogen/diesel energy ratio. High-speed imaging of the natural combustion luminosity was taken from a heavy-duty optically accessible engine. The engine was modified to include a single hole, side mounted injector for 35 MPa hydrogen direct injection into the combustion chamber. The eight-hole diesel injector remained in the original centrally mounted position, serving as a pilot flame ignition source. The results showed that reduced hydrogen energy share causes an increase in size and intensity of the diesel pilot acting to accelerate the initial combustion reaction, which is not only due to the increased diesel quantity but also the shift in diesel flame distribution. However, the combustion transitions into a near identical mixing-controlled combustion phase regardless of energy share. For hydrogen injection timing variations at fixed 90 % energy share, advanced injection was found to directly impact the hydrogen combustion mode altering the proportion of fuel injected prior to ignition of the diesel flame and the extent of mixing that has occurred. The longer residence time also increases the overlap of the two fuels prior to ignition resulting in a lengthened ignition delay due to dilution of the diesel pilot. The combustion phasing control is however preserved as the reaction was faster with a more premixed hydrogen charge at ignition.

Split injection is widely used in conventional spark ignition engines to control mixture formation. To utilise split injection in a hydrogen direct injection engine, it is important to understand gas jet development and its variations with injection timing. This is because prolonged duration of gaseous fuel injection is required due to lower energy per volume than that of the liquid fuel, which causes complex jet-tumble interactions. The ambient air pressure and density during the gas injection also changes depending on the injection timing, adding more complexity. This study performs endoscopic high-speed imaging of gas jet laser shadowgraph in an inline four-cylinder low-pressure direct-injection spark ignition (H2LPDI) engine equipped with a side-mounted, outward opening pintle nozzle injector. Due to safety concern and its known similarity in macroscopic jet developments, helium was used as an alternative gas to hydrogen. The results showed that the gas jet development changes greatly with the split injection timing selected with respect to the intake valve closure (IVC). For pre-IVC split injection, the first jet and second jet exhibited a very similar jet structure with statistically identical spreading angle and mixture centroid because both injections occurred at low air density conditions. However, the first injection showed a higher penetration rate and jet mixing rate, suggesting a complex interplay with the intake air flow. For post-IVC split injection, the second jet showed a narrower spreading angle due to lifted lower part of the jet, suggesting a strong influence of tumble flow. As the split injection was executed after the IVC, the developing tumble flow significantly accelerated jet penetration for the first injection. However, by the time that the second injection was executed, the tumble flow structure became well defined to hinder the second jet penetration. Indeed, the mixture centroid position was more lifted for the second jet evidencing the significant influence of developing tumble flow.

This study investigates the ignition characteristics of hydrogen double injection under a split-injection schedule with varying dwell times, focusing on their influence on ignition delay and flame development. Experiments were conducted in a constant-volume combustion chamber (CVCC) with optical access, replicating compression-ignition engine-like conditions. The baseline environment featured a quasi-quiescent ambient with a 23.8 kg/m3 gas density, a 21 vol.% O2 concentration, and a core temperature of 1000 K. High-speed Schlieren imaging, pressure trace analysis, jet mixing modeling, and constant-pressure homogeneous reactor (CHR) simulations were utilized to characterize the combustion process. Single-injection cases were also analyzed for comparison. The results revealed that, at the baseline 1000 K condition, the first injection advanced the ignition delay of the second injection significantly, reducing the ignition delay time from 9.66 ms for a single injection to as low as 0.62 ms relative to its start of injection, depending on dwell time. However, excessively short dwell times (e.g., 1 ms) led to reduced ignition events, attributed to interactions between closely spaced injections. Longer dwell times facilitated a more robust ignition. CHR simulations highlighted the role of elevated local temperatures and flame intermediates from the pilot injection in influencing the subsequent ignition processes. Temperature variation studies at 1030 and 970 K revealed that, while trends at 1030 K aligned with the baseline, ignition was not achieved at 970 K for either single-injection or split-injection cases with the same injection schedules as other temperature cases. However, increasing the first injection quantity and extending the dwell time enabled ignition at lower temperature, emphasizing the sensitivity of the strategy to ambient conditions. These findings highlight the potential of double injection strategies for robust hydrogen ignition in compression-ignition engines while underscoring the need for optimized injection parameters tailored to the operating conditions.

This study investigates the effects of varying fuel injection sequence, dwell time, ambient temperature (780-1050 K) and oxygen (O 2 ) (21-10 vol.%) on ignition and development of interacting n-heptane (pilot fuel) and methane (main fuel) jet flames under engine-relevant conditions. The results show that under baseline conditions (890 K and 21 vol.% O 2 ), when n-heptane is injected before methane (pilot-main injection sequence), with a longer dwell time, the burnt pilot-fuel products undergo mixing and cooling, necessitating prolonged jet-jet interaction before methane jet ignition. When n-heptane is injected after methane (main-pilot injection sequence), the amount of methane injected and mixed before pilot ignition affects the heat release, with a longer dwell time leading to a higher peak heat release. Regarding flame lift-off behavior, the entrainment of the pilot-fuel products into the methane jet leads to an upstream shift in the flame base. In the pilot-main injection case with the longest dwell time, the extended interaction period before main jet ignition allows the pilot-fuel products to interact with a larger portion of the methane jet. In some cases, this results in the formation of a detached ignition kernel upstream of the primary flame body downstream, impacting the flame stabilization and heat release characteristics. Under lower ambient temperature and reduced O 2 conditions, the flame lift-off exhibits transient or no stabilization before the flame base shifts downstream. This occurs despite the continued entrainment of pilot-fuel products into the methane jet.

Methanol, as a renewable fuel, is an attractive option for internal combustion engines. The dual direct injection method is one of the most promising strategies for applying methanol fuel in diesel engines as the flexible injection control enables combustion mode switching. In this study, a 1-L single-cylinder common-rail diesel engine with a compression ratio of 17.4 is retrofitted by installing an additional methanol direct injector with 35 MPa injection pressure. The engine is operated at 1400 rpm, intermediate load, and fixed midpoint combustion phasing of 10 °CA aTDC with a fixed total amount of energy while applying an energy substitution principle with up to 70% energy supplied by methanol. From the experiments, three distinct combustion modes were identified. When early methanol injection timings were selected in the range of 180–60 °CA bTDC, the primary combustion mode was premixed burn. Late injection timings of 10 °CA bTDC to TDC led to heat release rate shapes of the diffusion flame mode. In between these injection timings, partially premixed combustion was achieved where the higher methanol substitution ratio achieved carbon dioxide (CO2) emissions reduction by up to 11% and nitrogen oxides (NOx) emission suppression by up to 12%. It was also found that with increasing methanol energy substitution ratio, a significant reduction in smoke emissions was achieved. However, the decreased power output and increased emissions of unburnt hydrocarbon (uHC) and carbon monoxide (CO) were measured due to incomplete combustion caused by lower flame temperature of methanol.

The present study applies high-speed Mie-scattering spray imaging and flame image velocimetry (HS-FIV) to a jet fuel flame in a small-bore optical compression-ignition engine. The integration of sustainable aviation fuel (SAF) into the jet fuel supply may introduce challenges for stable engine operation due to low fuel reactivity. To resolve this issue, the engine is equipped with an ignition assistant plug providing additional heat into the compressed air. The impact of ignition assistant on the combustion of low reactivity fuel varies with injector tip protrusion, requiring detailed optical analysis to evaluate how the spray targeting changes relative to the piston bowl and thermal distributions. An optical engine is operated on a blend of 40% SAF and 60% F-24, a conventional jet fuel with mil-spec additives. The injector tip protrusion was varied between 1.5 and 4.5 mm below the cylinder head and for each protrusion, the high-speed movies were obtained with 30 cycles for sprays and 100 cycles for flames to address uncertainty concerns. The spray images were post processed via image binarisation to compute the liquid penetration length. An ensemble averaging method was applied to the FIV-derived flow fields to show the in-flame flow structure development while a spatial filtering approach was used for flow turbulence and combustion stability analysis. The spray image results exhibited decreased liquid penetration length and higher vaporisation for deeper injector tip protrusion, indicating higher temperature within the piston bowl. When the ignition assistant plug was activated, the FIV results showed similar overall flow structures and flow magnitude distribution to the plug off condition despite more advanced combustion phasing. However, lower cyclic variation was measured for the plug on condition, indicating more stable combustion as a key benefit of the active energy assistance. Regarding the injector tip protrusion variation, the shortest depth of 1.5 mm showed more retarded combustion phasing and lower peak pressure than those of 3.0 mm despite higher wall bounced-off flow magnitude. Enhanced vaporisation of the tested fuel blend as the injector tip was positioned deeper into the bowl was a likely cause of this observed trend. However, as the injector tip was protruded further to 4.5 mm, the combustion phasing was also more retarded and peak pressure was lower than those of 3.0 mm. Detailed flow field analysis showed lower magnitude flow vectors were observed for 4.5 mm depth as the jet impinged more on the floor of the piston bowl than the wall. The decreased wall bounce-off flow for deeper injector tip protrusion also led to lower flow turbulence measured in the r -θ plane. This outperformed higher fuel vaporisation expected, and thus the injector tip protrusion depth of 3 mm showed the most advanced combustion phasing and lowest cyclic variations.

This study aims to characterise the flame development for hydrogen-diesel dual direct injection (H2DDI) in an optically accessible heavy-duty engine through high-speed imaging of the natural combustion luminosity. A single hole, side mounted injector was used to inject H2 at 35 MPa in addition to a centrally mounted eight-hole diesel injector providing the ignition source for the H2. Firstly, the diesel pilot flame was examined without H2 to establish the combustion characteristics of the pilot flame. The pilot fuel energy was reduced from 1200 J to 120 J until the minimum repeatable diesel flame was found, which showed a flame distribution that transitioned from an initial quasi-steady diesel flame at peak load (1200 J), to a piston bowl wall-centric flame distribution (840 J) and then to an injector centric flame (120 J). The minimum pilot fuel quantity of 120 J was then used to investigate the ignition process of hydrogen main fuel mixtures supplying 90% energy and only 10% energy from diesel. The images showed three distinct stages of flame development. Firstly, the ignition of diesel pilot fuel occurs prior to interaction between the two fuels, as the H2 requires time to penetrate to the centre of the cylinder where the diesel pilot flame forms. Prior to ignition, the H2 jet penetrates towards the ignition source whilst it is simultaneously spread clockwise by the swirl flow. The second stage of flame development commences as the ignition of this H2 jet occurring after a period of interaction with the burnt products of the diesel pilot. Upon ignition, the H2 flame propagates upstream through the partially premixed H2 mixture and towards the H2 injector. Following the initial flame propagation, the combustion rate reduces as the transition into a diffusion mode occurs, i.e. the third stage of the flame development, with continued steady reaction zone growth, aided by the swirl flow. This three-stage ignition and flame development does not change with varied diesel pilot injection timing as evidenced by the flame images with only delayed phasing for later diesel pilot injection timing. However, the diesel pilot flame merges with the newly propagating H2 flame and thus the later diesel pilot injection timing leads to higher peak flame size and intensity.

Understanding the transient heat transfer mechanism of impinging flames is a crucial pathway for further improving the thermal efficiency of already efficient compression ignition (CI) engines. In this paper, the investigation of the transient heat transfer of wall-impinging flames was performed in a high-pressure constant-volume vessel. Fast-response thermocouples were installed in the impinging wall to record the transient heat flux. Two-color pyrometry was employed to estimate the mean temperature inside the flame region. Firstly, the transient heat transfer characteristics were investigated under varied ambient density, oxygen concentration, temperature, and injection pressure conditions. The optical flame velocity calculation method was applied to this extensive dataset to develop a heat transfer correlation between Nu and Re with which transient heat transfer coefficients were calculated and compared with the experimental results. From this analysis, cumulative fuel injection velocity was developed as the new characteristic parameter to characterize the transient heat transfer of the wall-impinging flames. Results indicate that the effect of fuel injection pressure on the heat flux is more significant than that of ambient gas conditions, with higher injection pressure causing higher heat flux through the impinging wall. No obvious linear tendency of transient Nu and Re was found when using the optical measurement results of the wall-impinging flame as the characteristic parameter. Instead, the cumulative fuel injection velocity shows a strong linear trend of transient Nu and Re during the transient heat transfer processes of the wall-impinging flame. Moreover, the heat transfer coefficients from the new cumulative fuel injection velocity well fit the experimental results.

This study aims to find the impact of the nozzle shape of a side-mounted, 3.5-MPa pintle injector on hydrogen concentration and flame development in a low-pressure direct-injection spark ignition (H2LPDI) engine. To this end, endoscopic high-speed imaging of gas jet laser shadowgraph and flames as well as spark-induced breakdown-spectroscopy (SIBS) method are applied to one of the inline four cylinders of H2LPDI engine. Two engines with endoscopic access are used: one motored engine for high-speed laser shadowgraph imaging of gas jet development and the other combustion engine for SIBS-based spark gap lambda measurements and high-speed hydrogen flame imaging. The gas jet visualisation showed that a nozzle with a narrower jet spreading angle leads to more turbulent jet boundaries and the jet axis being directed more towards the piston. Due to higher axial momentum, the narrower spreading angle nozzle also caused enhanced jet penetration across the in-cylinder tumble flow. This jet development pattern resulted in locally leaner hydrogen mixtures near the centrally mounted spark plug at the time of ignition, evidenced by a higher difference between spark gap lambda and global lambda. As a result, the flame size was measured smaller at any fixed combustion stage. For both nozzle types, the injection timing was also varied between 150 and 120 degrees CA bTDC but there was no significant difference measured in spark gap lambda and flame size compared to that associated with the nozzle type.

This study achieves combustion applications of methanol-diesel dual-direct injection in a retrofitted diesel engine by investigating methanol sprays and engine performance/emissions. Methanol draws high attention due to its green production potential and ease of adaptation to existing combustors and supply infrastructure. One of the most promising methods for utilising methanol in diesel engines is the dual direct injection, which provides a wide operating range and flexible injection control. This study provides an effective solution for dual direct injection by implementing a nozzle cap idea, which can mount a conventional direct injector for methanol delivery in an existing diesel engine. The custom-made nozzle cap can provide hole orientation variations, which effectively controls the methanol-air mixture distributions within the piston bowl. To this end, methanol sprays formed through the three-hole nozzle cap are analysed for varied injector pressure of 15 similar to 35 MPa. High-speed schlieren imaging confirmed working of the new nozzle for methanol injection with expected results of increased liquid penetration length and cone angle for higher injection pressure. The spray images also helped understand how the mixtures would be distributed within the piston bowl due to direct injection. Experiments performed on a 1-litre single-cylinder common-rail diesel engine operating at 1400 rpm, up to 70 % methanol energy fraction and a broad range of methanol injection timings of BDC to TDC, showed that the methanol-diesel dual direct injection combustion produces overall lower power output than the diesel baseline due to lower calorific value and flame temperature of methanol but significantly reduced CO2 emissions by up to 16 % and very low smoke emissions. The results showed high sensitivity to methanol injection timings and energy fraction in terms of the measured pressure, derived heat release rate and produced power due to an increase in mixture homogeneity for earlier injection timings and stratified charge conditions for later injection timings. However, the nozzle orientation change and expected methanol-air mixture distributions showed no measurable impact on pressure and heat release rate as well as engine power output and combustion stability. The most significant impact of the methanol three-hole nozzle orientation and resulting mixture distributions was found from uHC and NOx emissions because a nozzle orientation directing methanol more towards the corner of the piston bowl opposite side of the injector led to increased liquid wall wetting and methanol in crevice volumes and thereby causing less complete combustion for higher uHC and lower NOx. The low sensitivity of methanol mixture distributions to the in-cylinder pressure and engine power output but the measurable impact found on uHC and NOx emissions empathies the required optimisation of methanol direct injector nozzle depending on the combustion chamber design of the base diesel engine.

Hydrogen-diesel dual direct-injection (H2DDI) engines present a promising pathway towards cleaner and more efficient transportation. In this study, hydrogen split injection strategies were explored in an automotive-size single-cylinder compression ignition (CI) engine, with a focus on varying the injection timings and energy fractions. The engine was operated at an intermediate load with fixed combustion phasing through adjustments of pilot diesel injection timing. An energy substitution principle guided the variation in energy fraction between the two hydrogen injections and then diesel injection while keeping the total energy input constant. The findings demonstrate that early first hydrogen injection timings lead to characteristics indicative of premixed combustion, reflecting a high homogeneity of the hydrogen-air mixture. In contrast, hydrogen stratification levels were predominantly influenced by later second injection timings, with mixing-controlled combustion behaviour apparent for very late injections near top dead centre or when the second hydrogen injection held high energy fractions, which led to decreased nitrogen oxides (NOx: NO and NO2) emissions. The carbon dioxide (CO2) emissions did not show high sensitivity to the hydrogen split injection strategies, exhibiting about 77 % reduction compared to the diesel baseline due primarily to increased hydrogen energy fraction of up to 90 %.

Introduction: Air pollution is a significant global concern due to its adverse impact on public health even at low levels. In Australia, the transportation sector is a major contributor to greenhouse gas and other air pollution emissions, which are known to increase the risk of heat stress, cause respiratory illness, and spread infectious diseases. Hence, evaluating the economic burden is important for policy decision-making and mitigation efforts made on clean energy technologies. Methods: This study employed an epidemiology-based exposure-response function to estimate the number of health cases attributed to transport-related air pollution. PM10 was chosen to capture the overall health effect of transportation emission-related pollutant. The value of statistical life was computed using a refined human-capital approach that considers the loss of productivity at formal workplaces, as well as the loss of household and community production. The total economic burden combined the costs of mortality and morbidity cases. Results: The analysis results suggested that in 2018, based on the assumptions of this study, transport emissions contributed towards 1,000 to 2,550 premature deaths and approximately 26,700 incidences of cardiovascular hospitalisations, asthma attacks, and chronic obstructive pulmonary disease episodes, resulting in a total economic burden of A$910 million. Conclusion: The cost estimation provides an estimate of the economic burden due to transport-related pollution. With more up-to-date emission measurements, more detailed assessment of utilising surrogate pollutant, and more accurate pollutant threshold level for health effect, the current estimation can be updated in the future.

This study investigates the ignition and combustion characteristics of intersecting diesel surrogate (pilot) and hydrogen (H2, main) jets under engine-relevant conditions. The experiments, performed in an optically accessible constant-volume combustion chamber (CVCC), utilised two converging single-hole injectors, with the pilot fuel accounting for 12% of the total injected fuel energy. This study investigated the effects of two key parameters on the ignition process: jet interaction angle (12° to 19°) and ambient O2 concentration (10 to 21 vol.%). The results show that the presence of H2 either advances or delays pilot ignition depending on whether the pilot n-heptane jet ignites before or after interacting with the H2 jet, respectively. The pilot-main ignition transition period is influenced by both jet interaction angle and ambient O2 concentration. Under identical ambient conditions, a smaller jet interaction angle results in a longer transition, while for a constant angle, lower ambient O2 leads to a more prolonged transition. Under 10 vol.% O2 conditions, flame kernels emerge upstream of the main flame body, before eventually merging with the reacting jet downstream, with this phenomenon observed to induce variation in heat and flame stabilisation characteristics. An explanation for the upstream kernel formation is offered based on the entrainment of residual pilot n-heptane-jet fuel into the upstream region of the still-injecting main jet, with the relative jet momentum a likely key contributor influencing this entrainment that impacts kernel formation.

This study develops spark induced breakdown spectroscopy (SIBS) for measurements of direct injected hydrogen concentration in a multi-cylinder engine operated at real conditions. To this end, calibration is performed in the air excess ratio (λ) range of 2.1 ∼ 2.9 and simultaneously, high-speed schlieren imaging of laminar hydrogen flame propagation is performed in an optical high-pressure constant volume combustion chamber (CVCC). To achieve real engine applications, the SIBS is further developed using a modified conventional spark plug for sapphire window insertion onto the positive electrode and guided arc formation via a newly designed nipple type ground electrode. Specifically, the peak spectra intensity ratio of Hα (656 nm) to O (777 nm) is used for calibration, which shows a linear correlation with λ. For the first time, the calibrated SIBS is applied to a real engine operated at 46.2 ∼ 63.9 Nm load and 2000 rpm with 3.5 MPa hydrogen direct injection. The results show lower local λ than the global λ despite early injection timing of 165 crank angles before top dead centre, indicating a significant influence of in-cylinder flow motion on the spatial distribution of hydrogen-air mixtures.

This study investigates the ignition and combustion characteristics of interacting hydrogen (H2) and diesel surrogate jets under simulated compression-ignition engine conditions. The experimental setup includes two converging single-hole injectors in an optically accessible constant-volume combustion chamber (CVCC). The parameters varied in the study are fuel injection durations and ambient O2 concentrations (10 to 21 vol.%). The results show that a longer interaction between the diesel products and the H2 jet is required to achieve ignition of the H2 jet at lower O2 concentrations. Once ignited, the flame stabilises near or at the nozzle, except under the lowest ambient O2 condition of 10 vol.% where a lifted flame is observed. The lift-off response, however, is influenced by the relative injection duration of the fuels, with the interaction between the incoming H2 jet and the diesel combustion recession products possibly playing a role. The interaction between the jets also affects the recorded intensity and the distribution of the diesel fuel jet soot zone.

This study presents the experimental investigation of the ignition and subsequent combustion spreading sequences of hydrogen jets issued from a single-hole nozzle into a constant-volume combustion chamber. The hydrogen jet flames, forced ignited using a laser-induced plasma ignition, were monitored using high-speed schlieren imaging and pressure trace measurements. The parameters varied include the laser ignition location (axial or radial positions), laser ignition timing and the ambient oxygen level (10-21 vol.%). An analysis of the jet flame evolution reveals that the reaction front of the hydrogen jet spreads from the forced ignition site to engulf the entire downstream jet volume and recedes towards the nozzle. The results reveal that the ignition parameters and ambient oxygen condition in which it occurs can impact the jet flame recession and stabilisation characteristics. When ignition occurs sufficiently downstream or at the jet head periphery, the flame may not attain astable lift-off within the specified injection period. Additionally, lower ambient oxygen levels lead to slower flame recession towards the nozzle. Furthermore, the heat release profile of the hydrogen jet flame exhibits dependence on both the laser ignition parameters and ambient oxygen level.

This study investigates the techno-economic feasibility of a photovoltaic power plant integrated with hydrogen energy storage and a dual-fuel reciprocating engine for gas-to-power and power-to-gas operations. The system is optimised for maximising constant grid supply, minimising CO2 emissions, and lowering the levelised cost of electricity (LCOE) to assess its value in future energy landscape. Multi-objective optimisation identified a configuration with a hydrogen-fuelled engine generator offering a constant 10 MW grid supply with minimal CO2 emissions (78 kg/MWh), at a LCOE of $335.52/MWh. This system comprises a 93 MW PEM electrolyser, a 4 MW compressor, and 29 t of compressed hydrogen storage, within the limits of the industry’s current or projected capacities. A key highlight of the engine-based approach is its ability to readily enhance grid supply through increased diesel consumption without significantly impacting LCOE, provided CO2 emissions stay within acceptable sector cap. This flexibility surpasses alternative technologies. Further analysis explored potential LCOE reductions using global projected data, bringing optimised LCOE values down to $138.76/MWh, making it competitive to current market prices. Sensitivity analysis revealed the LCOE’s highest sensitivity to the discount rate, followed by minimal impact from variations in fuel and electricity prices due to the optimised system configuration. Furthermore, the tightening CO2 emission limits do not affect the optimised system’s performance, except for limiting the maximum achievable grid supply in 2050 by increased diesel reliance.

This work investigates the jet penetration, ignition, and combustion characteristics of methane (CH4), hydrogen-methane blend (H-2-CH4), and hydrogen (H-2) under various simulated direct-injection compression-ignition engine-relevant conditions. High-speed schlieren, pressure trace, and photodiode measurements were employed within a constant volume combustion chamber (CVCC). Experimental parameters were set to fixed values of the ambient density (24 kg/m(3)), oxygen concentration (21%), and reservoir pressure (20 MPa). The ambient temperature was maintained at 1060 K, a condition at which the jets were previously observed to exhibit varied ignition and flame stabilization behaviors. The study begins with an analysis of the injection system and nonreactive fuel jet penetration. The measurements show that introducing H-2 into CH4 consistently reduces the ignition delay and shifts the ignition location upstream. Optical imaging shows that all fuel jets exhibit different ignition patterns, namely, single-kernel, multi-kernel, and voluminous ignition patterns, with proportion-dependent on fuel compositions. The ignition pattern, as well as fuel composition, appear to impact the ensuing apparent heat release and flame stabilization characteristics. Flame luminosity measurements show the H-2 jet yielding the strongest broad-band emission among tested fuels.

This work extends the transported probability density function (PDF) method to model hydrogen–diesel dual direct injection (H2DDI) combustion, where a H2 jet is ignited by a small pilot diesel jet flame. The work is motivated by previous H2DDI engine tests where stable compression ignition engine operation was reported with up to 90 % H2 supply by energy share. To help explain this high performance and provide a tool to help further engine optimization, the Eulerian Monte Carlo Fields (EMCF) solution method is employed with which a transported PDF equation is solved in combination with Flamelet Generated Manifold (FGM) for high accuracy and computational efficiency. In all cases, the pilot fuel ignites before interacting with the H2 jet and thus reaction rate and chemical composition are computed as the weighted average of the corresponding values taken for two separated FGM tables generated for the two fuels. Pressure measurements and high-speed schlieren imaging performed in a preburn-type optical constant volume combustion chamber (CVCC) with n-heptane (nC7H16) pilot fuel were used to validate the EMCF+FGM model. The application focus is how H2 ignition and combustion is affected when the nC7H16 is injected prior to or after the main H2 jet. EMCF+FGM computed heat release rate and flame structure were compared with experimental data and results from conventional FGM model based on presumed PDF. When applied to H2DDI combustion, the EMCF+FGM model successfully reproduces flame structures and heat release rate under different injection strategies, including the transition towards partially-premixed combustion when the nC7H16 pilot follows the main H2 injection. Moreover, analysis of heat release rate from different stochastic fields can provide a useful indication about cyclic variability and combustion stability.