Evaluating low NOx hydrogen engines designed for off-road and construction applications

Hydrogen internal combustion engines offer a near-term decarbonisation pathway for hard to electrify sectors such as non-road mobile machinery (NRMM). However, few hydrogen-specific engines have ever been developed with the twin-goals of maximising low carbon energy efficiency and delivering air quality co-benefits. We present analyses of dynamometer-derived nitrogen oxides (NOx) tailpipe emissions from four variants of a ∼55 kW four-cylinder port fuelled injection spark ignition hydrogen internal combustion engine (H2ICE) suitable for a range of uses within the NRMM industry. Engine out (pre-aftertreatment) emissions are also reported for one of the H2ICE variants. The emissions were compared over the Non-Road Transient Cycle (NRTC) with an equivalent contemporary Stage V emissions compliant 55 kW diesel engine. All four H2ICE variants were configured to operate under lean burn conditions generating substantially lower NOx exhaust emissions over the NRTC when compared to the diesel engine. Lowest NOx emissions were observed for a spark ignition H2ICE with selective catalytic reduction and particulate filter (SCRF) aftertreatment. Tailpipe NOx emissions over the full NRTC for this configuration were 1.90 mg kWh−1, a greater than 99% reduction compared to diesel (3340 mg kWh−1) with lower average NOx emissions observed for the H2ICEs over all power, torque, and speed settings. The frequency and magnitude of transient (<20 ms) increases in NOx were also compared between diesel and H2ICE. A H2ICE using a hydrogen slip catalyst, but without SCRF aftertreatment, also emitted significantly lower tailpipe NOx than the diesel equivalent (63.7 mg kWh−1), a factor of greater than 50 times improvement over the NRTC. This creates a systems level dilemma: whether the additional small absolute reductions in NOx achieved using SCRF would have a net benefit that outweighed the broader financial and environmental costs of the SCR and exhaust fluid manufacture, distribution and possible small in-service ammonia slip from exhaust. Irrespective of aftertreatment system, the adoption of low NOx emitting H2ICE in NRMM, and particularly construction equipment, would appear to offer much greater near-term air quality benefits for cities when compared to switching to other low carbon alternatives such as biodiesel or hydrotreated vegetable oil

Investigating the size, morphology and composition of particulate matter released during transient and steady-state operation from a heavy-duty internal combustion engine running entirely on hydrogen

As hydrogen is explored for future propulsion, evaluating the morphology and chemical composition of lubricant oil-derived particles is crucial to understand the implications of our current path to decarbonisation, since existing data on such emissions is extremely limited. Particle size, count, morphology, and elemental composition were analysed from a spark-ignited hydrogen engine exhaust under two steady states (2400 rpm–50 Nm, 1300 rpm–150 Nm) and a 20-min transient cycle. Solid particle number was measured with a DMS500 and catalytic stripper; morphology and composition were analysed via transmission electron microscopy and EDX using graphene oxide and SiN grids with a novel particle collection method. At the high speed, particle concentration peaked at 3.14 × 107/cm3, with 80 % under 10 nm. Low speed showed 2.31 × 105/cm3. Particle size distribution nucleation modes were 7.5 nm (high speed), 8.66 nm (low speed) with most particles 500 nm clusters, crystalline structures and agglomerates. A ring pack redesign reduced oil consumption, lowering emissions for high-speed case to 2.14 ± 1.29 × 105/cm3. Compared to diesel, hydrogen cut particle number emissions by 98.8 %

Animal fat (tallow) as fuel for stationary internal combustion engines

The main aim of this thesis is to verify the suitability of waste animal fat, obtained from animal by-products in a process called rendering, as a fuel for internal combustion engines. This work is an attempt to provide guidance and minimal requirements for animal fat to be utilised as fuel. The properties of tallow were monitored on a weekly basis throughout a period of one year. Some properties, namely acidity, showed significant variability. Possible reasons causing variable and high acidity are given together with a proposal for an acidity removal method. The available laboratory facilities enabled the verification of changes in fat's viscosity, density, surface tension and lubricity in a range of temperatures. The impact of storage temperature on deterioration in tallow quality was investigated over a period of one month. The available emission control systems have been reviewed and a solution choice has been made, based on legal and economic criteria. A summary of two thousand hours operation of the 800 kW generating set using neat fat is provided. The renewable electricity generation subsidising system in the United Kingdom has been reviewed. A basic feasibility study for the installed generating set was prepared and the highest tallow price at which electricity generation is profitable was determined

Possible application of animal fat as engine fuel - lubricity aspects

Thepaperpresents results of animalfat lubricity testperformed at highfrequency reciprocating rig (HFRR). Impact of test temperature on wear scar diameter (WSD) is shown. Results for animal fat are compared with those for mineral diesel fuel (ULSD). Obtained WSD prooved excellent lubricating properties of animal fat. Laboratory test results are backed up with engine trials where two sets offuel pumps were tested on a large reciprocating engine. Animal fat can be used asfuelfor engines -when appropriatefiltrationprocess is implemented.</jats:p

Liquid Propane Injection in Flash-Boiling Conditions

This study aimed to investigate the influence of flash-boiling conditions on liquid propane sprays formed by a multi-hole injector at various injection pressures. The focus was on spray structures, which were analysed qualitatively and quantitatively by means of spray-tip penetration and global spray angle. The effect of flash boiling was evaluated in terms of trends observed for subcooled conditions. Propane was injected by a commercial gasoline direct injector into a constant volume vessel filled with nitrogen at pressures from 0.1 MPa up to 6 MPa. The temperature of the injected liquid was kept constant. The evolution of the spray penetration was observed by a high-speed camera with a Schlieren set-up. The obtained results provided information on the spray evolution in both regimes, above and below the saturation pressure of the propane. Based on the experimental results, an attempt to calibrate a simulation model has been made. The main advantage of the study is that the effects of injection pressure on the formation of propane sprays were investigated for both subcooled and flash-boiling conditions. Moreover, the impact of the changing viscosity and surface tension was limited, as the temperature of the injected liquid was kept at the same level. The results showed that despite very different spray behaviours in the subcooled and flash-boiling regimes, leading to different spray structures and a spray collapse for strong flash boiling, the influence of injection pressure on propane sprays in terms of spray-tip penetration and spray angle is very similar for both conditions, subcooled and flash boiling. As for the numerical model, there were no single model settings to simulate the flashing sprays properly. Moreover, the spray collapse was not represented very well, making the simulation set-up more suitable for less superheated sprays.</jats:p

Impact of Alternative Paraffinic Fuels on the Durability of a Modern Common Rail Injection System

Common rail (CR) diesel fuel injection systems are very sensitive to variations in fuel properties, thus the impact of alternative fuels on the durability of the injection system should be investigated when considering the use of alternative fuels. This work studies a high-pressure CR (HPCR) diesel fuel injection system operating for 400 h in an injection test bench, using a fuel blend composed of an alternative paraffinic fuel and conventional diesel (50PF50D). The alternative fuel does not have aromatic components and has lower density than conventional diesel fuel. The injection system durability study was carried out under typical injection pressure and fuel temperature for the fuel pump, the common rail and the injector. The results show that the HPCR fuel injection system and its components (e.g., piston, spring, cylinder, driveshaft and cam) have no indication of damage, wear or change in surface roughness. The absence of internal wear to the components of the injection system is supported by the approximately constant total flow rate that reaches the injector during the whole the 400 h of the experiment. However, the size of the injector nozzle holes was decreased (approximately 12%), being consistent with the increase in the return fuel flow of the injector and rail (approximately 13%) after the completion of the study. Overall, the injection system maintained its operability during the whole duration of the durability study, which encourages the use of paraffinic fuels as an alternative to conventional diesel fuel