Loop scavenged nozzle diffuser

Abstract

In certain embodiments, competitive performance levels may be facilitated by creating an in-cylinder air-fuel ratio (lambda) stratification characterized by center-rich mixture and lean mixtures at the periphery of the cylinder to ensure sufficiently rich mixture in the prechamber located at the center of the cylinder to prevent misfire, while assuring sufficiently lean mixture at the periphery of the cylinder where the concentration of the lubricating oil tends to be high, thereby preventing the occurrence of LOP. In certain embodiments, it may be very difficult to achieve center-rich lambda distribution with in-cylinder direct injection (DI). In certain embodiments, a specially designed injector tip nozzle diffuser including a converging scavenging slit and one or more converging diffuser holes may achieve in-cylinder center-rich fuel distribution while preventing high H2 concentration in the nozzle diffuser itself.

Description

[0001] LOOP SCAVENGED NOZZLE DIFFUSER

[0002] I. FIELD OF THE INVENTION

[0003] The disclosure generally relates to systems and methods for loop scavenged nozzle diffusers in internal combustion engines, and more particularly to methods and systems for using loop scavenged nozzle diffusers with H2 Internal Combustion Engines (ICEs) to enable combustion improvements.

[0004] II. BACKGROUND OF THE INVENTION

[0005] The following references describe problems with the state of the art that are more fully described below. These references are incorporated by reference herein to the extent consistent with this disclosure:

[0006] [1] Sotiropoulou, E., et al: Enabling Diesel -Like Performance in Heavy Duty H2-ICE via a Sophisticated Combustion System Solution, ATZ live Heavy Duty Engines 2024 - MTZ Conference, Germany, 2024.

[0007] [2] Sotiropoulou, E., et al: Same-Cycle Spark Control: The Future of Hydrogen Engines.

[0008] 13th Dessau Gas Engine Conference, Dessau, Germany, 2024.

[0009] [3] Sotiropoulou, E., et al: Holistic Solution Enabling High Power Density & Efficiency H2-ICE, ATZ live Heavy Duty Engines 2023 - MTZ Conference, Germany, 2023.

[0010] [4] Sotiropoulou, E., et al: Prechamber Combustion: Enabling the Competitive Carbon-Neutral ICE. In CIMAC Congress, Paper No. 291, Busan, S. Korea, 2023.

[0011] PATENT APPLICATION 1 Docket # PRO-OO 19-PCT[5] Sotiropoulou, E., et al: Breakthrough in Hydrogen Engine Combustion Enabling Zero Emissions and High Efficiency with Passive Prechamber Technology. In 12th Dessau Gas Engine Conference, Dessau, Germany 2022.

[0012] [7] Yasueda, S., et al: Predicting Autoignition caused by Lubricating Oil in Gas Engines. In CIMAC Congress, Paper No. 37, Shanghai, China, 2013.

[0013] [8] Sotiropoulou, E., et al: Prechamber Spark Plugs: The Evolution from Low Emission Natural Gas to Zero Emission H2 Operation. MTZ Worldwide, vol. 2020-6, pp. 46-50, 2020.

[0014] [9] Sotiropoulou, E., et al: Improving Efficiency of the Premixed Combustion by Reducing Cyclic Variability. In CIMAC Congress, Paper No. 257, Helsinki, Sweden, 2016.

[0015]

[0010] Zhu, S., et al: A Method for Developing Countermeasures for Lubricating Oil Preignition In Natural Gas Engines. In 9th Dessau Gas Engine Conference, Dessau, Germany 2016.

[0016]

[0011] Sotiropoulou E., et., all.: Active Scavenge Prechamber. U.S. Patent No. 9,850,806.

[0017]

[0012] Tozzi L., et., all.: Lean Burn Precombustion Chamber, U.S. Patent No. 10,208,561.

[0018] Decarbonization and sustainability mandates pose serious uncertainties to the future of Internal Combustion Engines (ICEs). Achieving levels of competitive efficiency and power density with zero-emissions, necessitates holistic system solutions for key engine components like ignition, injection, and combustion chamber which must be properly matched to meet performance targets with sustainable fuels like Hydrogen (H2) as discussed in References 1-8, Ammonia (NHs) and Methanol (CH3OH).

[0019] PATENT APPLICATION 2 Docket # PRO-OO 19-PCTDue to the challenges associated with combustion instabilities, the power density and efficiency of H2 engines are much lower compared to that of Diesel engines. Typical combustion issues with H2 Internal Combustion Engines (ICEs), defined as engines burning any fuel mixture combination that includes Natural Gas, Ammonia (NH3) and Hydrogen, or with carbon neutral fuels such as Methanol (CH3OH), Ethanol (C2H5OH), synthetic gasoline, etc., are large variations in the Coefficient of Variation of Indicated Mean Effective Pressure (COV-IMEP), high propensity to Lubrication Oil Preignition (LOP), Knock and Preignition as discussed in References 1-8 above. Because of these limitations, the levels of engine Indicated Mean Effective Pressure (IMEP), Indicated Thermal Efficiency (ITE) and Nitrous Oxide (NOx) emissions do not meet the performance level targets to be competitive with conventional ICEs.

[0020] For example, the typical performance currently achieved with H2 engines is:

[0021] - COV-IMEP > 2%

[0022] — IMEP < 16 bar

[0023] - ITE < 41 %

[0024] — Nox > 100 mg / Nm3

[0025] On the other hand, the competitive performance levels needed for H2 engines are:

[0026] - COV-IMEP < 1 %

[0027] — IMEP > 20 bar

[0028] - ITE > 49 %

[0029] — NOx < 25 mg / Nm3

[0030] There is a need to address the foregoing deficiencies in the art.

[0031] PATENT APPLICATION 3 Docket # PRO-OO 19-PCTIII. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 depicts a perspective view of an in-cylinder Lambda ( ) distribution in a combustion chamber in accordance with certain embodiments.

[0033] Figure 1A depicts cross-sectional and perspective views of the combustion chamber of Figure 1 in accordance with certain embodiments.

[0034] Figure 2 depicts an advanced start of combustion (SOC) cycle in accordance with certain embodiments.

[0035] Figure 3 depicts top and perspective views of an in-cylinder Lambda (X) distribution of the injector cap of Figure 4 in accordance with certain embodiments.

[0036] Figure 4 depicts a conventional Direct Injection (DI) injector cap with 5 large holes on one side aimed towards the center of the cylinder in accordance with certain embodiments.

[0037] Figure 5 depicts an injector nozzle diffuser in accordance with certain embodiments.

[0038] Figure 6 depicts isometric views of an injector nozzle diffuser in accordance with certain embodiments.

[0039] Figure 7 depicts top and perspective views of an in-cylinder Lambda (X) distribution for the injector nozzle diffuser of Figure 6 in accordance with certain embodiments.

[0040] PATENT APPLICATION 4 Docket # PRO-OO 19-PCTIV. DETAILED DESCRIPTION

[0041] In certain embodiments shown in Figure 1, main combustion cylinder 100 may have one or more intake valves 110 and one or more exhaust valves 120. In certain embodiments, competitive performance levels may be facilitated by creating an in-cylinder air-fuel ratio (lambda) stratification characterized by rich mixture 130 in the center of the cylinder 100 (center-rich) and lean mixtures 140 at the periphery of the cylinder as discussed in References 9-10 above and as shown in Figure 1. In certain embodiments, such center-rich lambda distribution may ensure sufficiently rich mixture 130 in the prechamber 150 located at the center of the cylinder 100 to prevent misfire, while assuring sufficiently lean mixture 140 at the periphery of the cylinder 100 where the concentration of the lubricating oil tends to be high, thereby preventing the occurrence of LOP. In certain embodiments, the main combustion cylinder 100 may include prechamber 150 and injector tip cap 340 as shown in Figure 1A.

[0042] In certain embodiments, an injector nozzle diffuser, is disclosed comprising: an external surface and an internal surface enclosing an inner volume; a scavenging slit comprising a scavenging inlet for communicating with a main combustion chamber and a scavenging outlet communicating with the inner volume for introducing a scavenging flow from the main combustion chamber into the inner volume; and one or more converging diffuser holes each comprising a diffuser inlet for communicating with the inner volume and a diffuser outlet for communicating with the main combustion chamber; wherein the scavenging inlet comprises a scavenging inlet area at the external surface and the scavenging outlet comprises a scavenging outlet area at the inner surface and wherein the scavenging inlet area is larger than the scavenging outlet area to accelerate the scavenging flow into the inner volume; and wherein each diffuser inlet comprises a diffuser inlet area at the internal surface and each diffuser outlet comprises a diffuser outlet area at the external PATENT APPLICATION 5 Docket # PRO-OO 19-PCTsurface and wherein each diffuser inlet area is larger than the diffuser outlet area to accelerate the scavenging flow out of the inner volume; and wherein the scavenging flow is configured to remove residual fuel from the inner volume via the one or more converging diffuser holes.

[0043] Each of the one or more converging diffuser holes may comprise a degree of convergency defined as the diffuser inlet area / diffuser outlet area. The one or more converging diffuser holes may comprise a plurality of different degrees of convergency selected to generate a center rich air-fuel distribution in the main combustion chamber. Each of the one or more converging diffuser holes may comprise an orientation defined as the direction of each hole axis with respect to the engine cylinder center axis. The one or more converging diffuser holes may comprise a plurality of different orientations selected to generate a center rich air-fuel distribution in the main combustion chamber.

[0044] The main combustion chamber may comprise a global average air-fuel mixture (Agiobai), an air-fuel mixture at the center of the main combustion chamber (Acenter), and an air-fuel mixture at the periphery of the main combustion chamber (^periphery), wherein the plurality of different degrees of convergency are configured to generate Center > ^periphery. In certain embodiments, Acenter > 1.1 Aglobal. In certain embodiments, periphery < 0.90 giobai.

[0045] The plurality of different degrees of convergency may be configured to achieve in-cylinder center-rich fuel distribution while preventing high fuel concentration in the inner volume. The fuel may comprise one or more of Hydrogen (H2), Ammonia (NH3) and Methanol (CH3OH). The plurality of different degrees of convergency and the diffuser outlet area of each of the one or more converging diffuser holes may be configured to generate flow velocity magnitude and direction necessary to achieve a desired distribution of fuel concentration in the main combustion chamber. The one or more converging diffuser holes may comprise a plurality of different diffuser outlet

[0046] PATENT APPLICATION 6 Docket # PRO-OO 19-PCTareas. The plurality of different degrees of convergency and the plurality of different diffuser outlet areas may be configured to generate flow velocity necessary to achieve a desired distribution of fuel concentration in the main combustion chamber. The one or more converging diffuser holes and the scavenging slit may be located on the nozzle diffuser and the nozzle diffuser may be located with respect to a spark plug or prechamber in the main combustion chamber to achieve a center-rich lambda distribution.

[0047] In certain embodiments, a method of loop scavenging is disclosed, comprising: providing an injector nozzle diffuser, comprising: an external surface and an internal surface enclosing an inner volume; a scavenging slit comprising a scavenging inlet for communicating with a main combustion chamber and a scavenging outlet communicating with the inner volume; and one or more converging diffuser holes each comprising a diffuser inlet for communicating with the inner volume and a diffuser outlet for communicating with the main combustion chamber; introducing a scavenging flow from the main combustion chamber into the inner volume to push residual from the inner volume via the one or more converging diffuser holes; and injecting a fuel flow into the main combustion chamber via the one or more converging diffuser holes; wherein the scavenging inlet comprises a scavenging inlet area at the external surface and the scavenging outlet comprises a scavenging outlet area at the inner surface and wherein the scavenging inlet area is larger than the scavenging outlet area to accelerate the scavenging flow into the inner volume; and wherein each diffuser inlet comprises a diffuser inlet area at the internal surface and each diffuser outlet comprises a diffuser outlet area at the external surface and wherein each diffuser inlet area is larger than the diffuser outlet area to accelerate the scavenging flow out of the inner volume. The scavenging flow may be introduced into the inner volume during a compression stroke.

[0048] PATENT APPLICATION 7 Docket # PRO-OO 19-PCTEach of the one or more converging diffuser holes may comprise a degree of convergency defined as the diffuser inlet area / diffuser outlet area. The one or more converging diffuser holes may comprise a plurality of different degrees of convergency to generate a center rich air-fuel distribution in the main combustion chamber. Each of the one or more converging diffuser holes comprises an orientation defined as the direction of each hole axis with respect to the engine cylinder center axis. The one or more converging diffuser holes may comprise a plurality of different orientations to generate a center rich air-fuel distribution in the main combustion chamber.

[0049] The main combustion chamber may comprise a global average air-fuel mixture (Agiobai), an air-fuel mixture at the center of the main combustion chamber (Acenter), and an air-fuel mixture at the periphery of the main combustion chamber (^periphery), wherein the plurality of different degrees of convergency are configured to generate Center > ^periphery. In certain embodiments, Xcenter 1.1 Aglobal. In certain embodiments, ^periphery < 0.9 Xgiobai.

[0050] The plurality of different degrees of convergency may be configured to achieve in-cylinder center-rich fuel distribution while preventing high fuel concentration in the inner volume. The fuel may comprise one or more of Hydrogen (H2), Ammonia (NH3) and Methanol (CH3OH). The one or more converging diffuser holes may comprise a plurality of different diffuser outlet areas. The plurality of different degrees of convergency and the plurality of different diffuser outlet areas may be configured to generate flow velocity necessary to achieve a desired distribution of fuel concentration in the main combustion chamber. The one or more converging diffuser holes and the scavenging slit may be located on the nozzle diffuser and the nozzle diffuser may be located with respect to a prechamber in the main combustion chamber to achieve a center-rich lambda distribution.

[0051] PATENT APPLICATION 8 Docket # PRO-OO 19-PCTIn certain embodiments, Figure 2 shows a sequence of consecutive engine combustion cycles leading to backfire in the intake (i.e., frontfire). In certain embodiments, Cycle #82210 shows a normal cycle. In certain embodiments Cycle #83220 shows an advanced start of combustion (SOC) which may be caused by either hot spots from improper management of high energy ignition or by lube oil preignition (LOP). In certain embodiments, Cycle #84230 shows an enhanced combustion Heat Released Rate cycle that may be caused by hot spots from the previous advanced SOC cycle 220. In certain embodiments, Cycle #85240 shows knock that may be caused by high temperatures from the preceding high combustion cycle 230. In certain embodiments, Cycle #86250 shows frontfire or preignition. This type of combustion instability may be typical in H2 engines and may prevent reliable operation at higher power densities above 16 bar brake mean effective pressure (BMEP). In certain embodiments, the instability may be initiated by an advanced start of combustion (SOC) cycle, which may be caused by either hot spots from improper management of high energy ignition sparks or by lubricating oil preignition (LOP) from in-cylinder rich pockets and may result in large cycle to cycle combustion variabilities.

[0052] In certain embodiments, the power density of an H2 engine may be less than 60% of its Diesel counterpart due to these combustion instabilities. For example, if the base Diesel engine operates at 25 bar BMEP (brake mean effective pressure), the H2 engine version may operate at less than 15 bar BMEP before the combustion becomes unstable. In certain embodiments, if for the Diesel version the engine efficiency is in the range of 48%, for the H2 version the engine efficiency may be in the range of 40%.

[0053] In certain embodiments, center rich mixtures may prevent the occurrence of combustion instabilities at BMEP levels above 16 bar. In certain embodiments, combustion CFD studies, as well as engine testing, have indicated that it is very difficult to achieve center-rich lambda distribution PATENT APPLICATION 9 Docket # PRO-OO 19-PCTwith in-cylinder direct injection (DI). In certain embodiments, a specially designed injector tip nozzle diffuser that propagates fuel like H2, may achieve in-cylinder center-rich fuel distribution while preventing high H2 concentration in the nozzle diffuser itself.

[0054] In certain embodiments, a standard configuration of the injector tip cap may produce a lambda distribution as shown in Figure 3. As shown in Figure 3, the lambda distribution may be quite chaotic with areas of very lean mixture 310, including the spark plug region 320, and areas of very rich mixtures 330, including the injector tip cap volume 340. Having H2-lean pockets 310 where the spark plug 320 is located can cause delayed combustion and misfire. Furthermore, having H2-rich pockets 330, especially if located within the injector tip cap region 340 and at the periphery of the cylinder where the concentration of lubricating oil tends to be higher, can result in preignition within the injector tip cap 340 and in lubricating oil preignition (LOP) at the cylinder liner causing combustion instability limiting the engine power output and efficiency.

[0055] In certain embodiments shown in Figure 4, engine cylinder 400 may include injector tip cap 410 characterized by only large discharge orifices 420 located on one side and directed towards the center of the cylinder. For the configuration shown in Figure 4, the resulting in-cylinder lambda distribution, as shown in Figure 3, may be far from the desired center-rich distribution shown in Figure 1.

[0056] In certain embodiments as shown in Figures 5 and 6, fuel injector 500 may include injector nozzle tip 510 that may include loop scavenged nozzle diffuser 520 to improve H2 diffusion control. Loop scavenged nozzle diffuser 520 may include Converging Scavenging Slit 530 that is converging with respect to In-Flow Stream 540 during compression and one or more Diffuser Holes 550 that are converging with respect to Out-Flow Stream 560 during injection. In certain embodiments,

[0057] PATENT APPLICATION 10 Docket # PRO-OO 19-PCTcomputational flow dynamic (CFD) simulations have shown that the loop scavenge flow 570 may enable thorough evacuation of residual gases from prechambers during a compression stroke. When flow 540 enters the prechamber through the scavenging port 530, it may act as a fluid piston pushing the residual gas trapped in prechamber 580 out of the prechamber 580 and into the main chamber, which may be very effective in reducing the H2 concentration in the injector tip cap 520 following the injection process.

[0058] In certain embodiments, one or more high velocity streams 560 ensuing from the injector tip cap 520 may dramatically enhance the H2 diffusion control in the main combustion chamber enabling an in-cylinder center-rich lambda distribution. In certain embodiments, following fuel injection, while compression is still taking place, incoming flow streams 540 enter scavenging slit 530, get accelerated by the convergency of slit 530, loop around 570 inside diffuser volume 580, get accelerated through converging diffuser holes 550, and finally exit the diffuser volume 580 with high velocity 560 propagating at a controlled rate into the main combustion chamber.

[0059] In certain embodiments of Figures 5 and 6, unlike with the injector tip cap 410 depicted in Fig 4. the fuel, for example H2, can be accelerated through one or more converging holes 550 at different rates determined by the degree of convergency of each hole 550. Such acceleration rates may generate the desired center-rich lambda stratification. In certain embodiments, the orientation of converging diffuser holes 550, defined as the direction of each hole axis 590 with respect to the engine cylinder center axis, may be configured to achieve in-cylinder center-rich fuel distribution. Similarly, for the loop scavenge, the convergent slit 530 may be configured with a degree of convergency to accelerate the flow streams going into diffuser volume 580 and act as a fluid piston to push the H2 fuel trapped in the diffuser volume 580 out in the main combustion chamber. In certain embodiments, the degree of convergency may be defined by the ratio between PATENT APPLICATION 11 Docket # PRO-OO 19-PCTthe hole / slit inlet area (Ai) and the hole / slit outlet area (A2). A hole / slit having the area ratio A1 / A2 > 2 may generate faster fuel streams than a hole / slit having area ratio A1 / A2 < 2. Depending on the incylinder charge density and flow velocity field, the number of holes 550 and the size of the slit 530 may be determined and each hole 550 and slit 530 may be configured with a specific hole / slit orientation and with a specific hole / slit outlet area and area ratio to generate the flow velocity necessary to achieve a desired concentration of fuel at any given region inside the cylinder, and necessary to achieve an effective scavenge of the fuel trapped in the diffuser volume 580.

[0060] The location of holes 550 and slit 530 on nozzle diffuser 520 with respect to the location of the prechamber 720 may be selected to achieve the desired center-rich lambda distribution. In certain embodiments as shown in figure 7, prechamber 720 may be located in the center of the cylinder and injector cap or nozzle diffuser 740 may be located on the side, adjacent to the cylinder liner, and the location of the one or more converging diffuser holes 550 may be asymmetric and grouped all on one side towards the spark plug or prechamber 720.

[0061] In certain embodiments, the degree of convergency, the exit areas and the orientation of one or more converging diffuser holes 550 and convergent slit 530 as well as the location of the one or more converging diffuser holes 550 and the convergent slit 560 on the nozzle diffuser 520 with respect to the prechamber location may be determined using validated computational fluid dynamic (CFD) as follows:

[0062] Step 1 - characterization of in-cylinder fluid dynamic and thermodynamic conditions. Flow velocity, pressure and temperature may be calculated for the entire cylinder volume, at each crank angle, throughout the intake and the compression events;

[0063] PATENT APPLICATION 12 Docket # PRO-OO 19-PCTStep 2 - simulation iterations of various holes geometries, numbers and locations to achieve the desired center-rich stratification. For example, in the center of the cylinder the lambda may be Center = Igiobai x 1.25, while at the periphery of the cylinder the lambda may be ^periphery = Lgiobai x 0.75, where giobai is the global average air-fuel mixture. One of skill in the art will recognize that the values of Center and ^periphery may be varied among a range of values where center > ^periphery without departing from the scope of embodiments of the invention.; and

[0064] Step 3 - simulation iterations of various scavenging slit geometries to achieve optimum loop scavenge defined as the maximum evacuation rate of residual fuel from the nozzle diffuser volume.

[0065] In certain embodiments as shown in Figure 7, interim results from a CFD simulation of the injector nozzle diffuser of Figures 5 and 6 achieve a significantly improved in-cylinder center-rich lambda distribution compared to the standard injector tip cap 340 depicted in Figures 1A and 3. As shown in Figure 7, injector nozzle diffuser of Figures 5 and 6 may achieve a much richer lambda 710 in the spark plug region 720 in the center of the cylinder, while maintaining a relatively leaner lambda 730 at the periphery of the cylinder and in the injector nozzle diffuser 740 region.

[0066] While the invention has been described with reference to the specific embodiments thereof, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the invention as defined by the appended claims. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, method, operation or operations, to the objective, spirit, and scope of the invention. All such modifications are intended to be within the scope of the claims appended hereto. In particular, while the methods disclosed herein have been described with reference to particular operations performed in a particular order, it will be understood that these operations may

[0067] PATENT APPLICATION 13 Docket # PRO-OO 19-PCTbe combined, sub-divided, or re-ordered to form an equivalent method without departing from the teachings of the invention. Accordingly, unless specifically indicated herein, the order and grouping of the operations are not a limitation of the invention.

[0068] PATENT APPLICATION 14 Docket # PRO-OO 19-PCT

Claims

V. CLAIMSWe claim:

1. An injector nozzle diffuser, comprising:an external surface and an internal surface enclosing an inner volume;a scavenging slit comprising a scavenging inlet for communicating with a main combustion chamber and a scavenging outlet communicating with the inner volume for introducing a scavenging flow from the main combustion chamber into the inner volume; andone or more converging diffuser holes each comprising a diffuser inlet for communicating with the inner volume and a diffuser outlet for communicating with the main combustion chamber;wherein the scavenging inlet comprises a scavenging inlet area at the external surface and the scavenging outlet comprises a scavenging outlet area at the inner surface and wherein the scavenging inlet area is larger than the scavenging outlet area to accelerate the scavenging flow into the inner volume; andwherein each diffuser inlet comprises a diffuser inlet area at the internal surface and each diffuser outlet comprises a diffuser outlet area at the external surface and wherein each diffuser inlet area is larger than the diffuser outlet area to accelerate the scavenging flow out of the inner volume; andwherein the scavenging flow is configured to remove residual fuel from the inner volume via the one or more converging diffuser holes.

2. The injector nozzle diffuser of claim 1, wherein each of the one or more converging diffuser holes comprises a degree of convergency defined as the diffuser inlet area / diffuser outlet area.PATENT APPLICATION 15 Docket # PRO-OO 19-PCT3. The injector nozzle diffuser of claim 2, wherein the one or more converging diffuser holes comprises a plurality of different degrees of convergency selected to generate a center rich air-fuel distribution in the main combustion chamber.

4. The injector nozzle diffuser of claim 1, wherein each of the one or more converging diffuser holes comprises an orientation defined as the direction of each hole axis with respect to the engine cylinder center axis.

5. The injector nozzle diffuser of claim 1, wherein the one or more converging diffuser holes comprises a plurality of different orientations selected to generate a center rich air-fuel distribution in the main combustion chamber.

6. The injector nozzle diffuser of claim 1, wherein the main combustion chamber comprises a global average air-fuel mixture (Agiobai), an air-fuel mixture at the center of the main combustion chamber ( center), and an air-fuel mixture at the periphery of the main combustion chamber (^periphery), wherein the plurality of different degrees of convergency are configured tO generate A,center > ^periphery.

7. The injector nozzle diffuser of claim 6, wherein Xcenter > 1.1 Xgiobai.

8. The injector nozzle diffuser of claim 6, wherein ^periphery < 0.90 Xgiobai.

9. The injector nozzle diffuser of claim 3, wherein the plurality of different degrees of convergency are configured to achieve in-cylinder center-rich fuel distribution while preventing high fuel concentration in the inner volume.

10. The injector nozzle diffuser of claim 1, wherein the fuel comprises one or more of Hydrogen (H2), Ammonia (NH3) and Methanol (CH3OH).

11. The injector nozzle diffuser of claim 3, wherein the plurality of different degrees of convergency and the diffuser outlet area of each of the one or more converging diffuser holesPATENT APPLICATION 16 Docket # PRO-OO 19-PCTare configured to generate flow velocity magnitude and direction necessary to achieve a desired distribution of fuel concentration in the main combustion chamber.

12. The injector nozzle diffuser of claim 3, wherein the one or more converging diffuser holes comprises a plurality of different diffuser outlet areas.

13. The injector nozzle diffuser of claim 12, wherein the plurality of different degrees of convergency and the plurality of different diffuser outlet areas are configured to generate flow velocity necessary to achieve a desired distribution of fuel concentration in the main combustion chamber.

14. The injector nozzle diffuser of claim 1, wherein the one or more converging diffuser holes and the scavenging slit are located on the nozzle diffuser and the nozzle diffuser is located with respect to a spark plug or prechamber in the main combustion chamber to achieve a center-rich lambda distribution.

15. A method of loop scavenging, comprising:providing an injector nozzle diffuser, comprising:an external surface and an internal surface enclosing an inner volume; a scavenging slit comprising a scavenging inlet for communicating with a main combustion chamber and a scavenging outlet communicating with the inner volume; and one or more converging diffuser holes each comprising a diffuser inlet for communicating with the inner volume and a diffuser outlet for communicating with the main combustion chamber;introducing a scavenging flow from the main combustion chamber into the inner volume to push residual from the inner volume via the one or more converging diffuser holes; andPATENT APPLICATION 17 Docket # PRO-OO 19-PCTinjecting a fuel flow into the main combustion chamber via the one or more converging diffuser holes;wherein the scavenging inlet comprises a scavenging inlet area at the external surface and the scavenging outlet comprises a scavenging outlet area at the inner surface and wherein the scavenging inlet area is larger than the scavenging outlet area to accelerate the scavenging flow into the inner volume; andwherein each diffuser inlet comprises a diffuser inlet area at the internal surface and each diffuser outlet comprises a diffuser outlet area at the external surface and wherein each diffuser inlet area is larger than the diffuser outlet area to accelerate the scavenging flow out of the inner volume.

16. The method of claim 15, wherein the scavenging flow is introduced into the inner volume during a compression stroke.

17. The method of claim 15, wherein each of the one or more converging diffuser holes comprises a degree of convergency defined as the diffuser inlet area / diffuser outlet area.

18. The method of claim 15, wherein the one or more converging diffuser holes comprises a plurality of different degrees of convergency to generate a center rich air-fuel distribution in the main combustion chamber.

19. The method of claim 15, wherein each of the one or more converging diffuser holes comprises an orientation defined as the direction of each hole axis with respect to the engine cylinder center axis.

20. The method of claim 18, wherein the one or more converging diffuser holes comprises a plurality of different orientations to generate a center rich air-fuel distribution in the main combustion chamber.PATENT APPLICATION 18 Docket # PRO-OO 19-PCT21. The method of claim 15, wherein the main combustion chamber comprises a global average air-fuel mixture (Agiobai), an air-fuel mixture at the center of the main combustion chamber ( center), and an air-fuel mixture at the periphery of the main combustion chamber (^periphery), wherein the plurality of different degrees of convergency are configured to generate Center > ^periphery.

22. The method of claim 21, wherein Xcenter > 1.1 Xgiobai.

23. The method of claim 21, wherein ^periphery < 0.9 giobai.

24. The method of claim 18, wherein the plurality of different degrees of convergency are configured to achieve in-cylinder center-rich fuel distribution while preventing high fuel concentration in the inner volume.

25. The method of claim 15, wherein the fuel comprises one or more of Hydrogen (H2), Ammonia (NH3) and Methanol (CH3OH).

26. The method of claim 18, wherein the one or more converging diffuser holes comprises a plurality of different diffuser outlet areas.

27. The method of claim 26, wherein the plurality of different degrees of convergency and the plurality of different diffuser outlet areas are configured to generate flow velocity necessary to achieve a desired distribution of fuel concentration in the main combustion chamber.

28. The method of claim 15, wherein the one or more converging diffuser holes and the scavenging slit are located on the nozzle diffuser and the nozzle diffuser is located with respect to a prechamber in the main combustion chamber to achieve a center-rich lambda distribution.PATENT APPLICATION 19 Docket # PRO-OO 19-PCT

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