Steve Rogak

Combustion in a heavy-duty direct-injection engine using hydrogen—methane blend fuels

Abstract Adding hydrogen to the fuel in a direct injection natural gas engine offers the potential significantly to reduce local and global air pollutant emissions. This work reports on the effects of fuelling a heavy-duty engine with late-cycle direct injection of blended hydrogen—methane fuels and diesel pilot ignition over a range of engine operating conditions. The effect of hydrogen on the combustion event varies with operating condition, providing insight into the fundamental factors limiting the combustion process. Combustion stability is enhanced at all conditions studied; this leads directly to a significant reduction in emissions of combustion byproducts, including carbon monoxide, particulate matter, and unburned fuel. Carbon dioxide emissions are also significantly reduced by the lower carbon—energy ratio of the fuel. The results suggest that this technique can significantly reduce both local and global pollutant emissions associated with heavy-duty transport applications while requiring minimal changes to the fuelling system.

Injection Parameter Effects on a Direct Injected, Pilot Ignited, Heavy Duty Natural Gas Engine with EGR

Pilot-ignited direct injection of natural gas fuelling of a heavy-duty compression ignition engine while using recirculated exhaust gas (EGR) has been shown to significantly reduce NO x emissions. To further investigate emissions reductions, the combustion timing, injection pressure, and relative delay between the pilot and main fuel injections were varied over a range of EGR fractions while engine speed, net charge mass, and oxygen equivalence ratio were held constant. PM emissions were reduced by higher injection pressures without significantly affecting NO x at all EGR conditions. By delaying the combustion, NO x was reduced at the expense of increased PM for a given EGR fraction. By reducing the delay between the pilot and main fuel injections at high EGR, PM emissions were substantially reduced at the expense of increased total hydrocarbon (tHC) emissions. In this research, no attempt was made to optimize the injector or combustion chamber for natural gas fuelling with EGR.

Effect of operating condition on particulate matter and nitrogen oxides emissions from a heavy-duty direct injection natural gas engine using cooled exhaust gas recirculation

Abstract Two methods for reducing nitrogen oxides (NOX) emissions from direct injection, compression ignition, heavy-duty engines are exhaust gas recirculation (EGR) and the high-pressure direct injection of natural gas. Tests combining these two techniques were carried out on a single-cylinder research engine (SCRE) based on a modified heavy-duty automotive engine. No attempt was made to optimize the engines combustion chamber or the injector geometry for EGR operation. The SCREs independent charge-air system allowed for more controlled testing over a wider range of test variables than can be carried out by a standard engine. These tests investigated the effects of cooled EGR on particulate matter (PM) and NOX emissions while varying the injection timing, engine speed, equivalence ratio and intake manifold pressure. The results suggested that, with EGR, higher equivalence ratios reduced power-specific NOX but increased PM emissions. Increasing the charge mass at a constant EGR fraction resulted in significant reductions in PM, at the cost of slightly increased NOX By advancing the injection timing at high EGR fractions, PM emissions and fuel efficiency were improved, with only a slight increase in NOX emissions compared to the more retarded injection timings. The engine speed influenced the amount of EGR that could be recirculated, with lower speeds resulting in higher achievable EGR fractions. These results suggest that EGR fractions in excess of 20 per cent can achieve NOX reductions beyond 75 per cent, without causing unacceptable increases in PM emissions or significant reductions in fuel efficiency.

Hydrogen-methane blend fuelling of a heavy-duty, direct-injection engine

Combining hydrogen with natural gas as a fuel for internal combustion engines provides an early opportunity to introduce hydrogen into transportation applications. This study investigates the effects of fuelling a heavy-duty engine with a mixture of hydrogen and natural gas injected directly into the combustion chamber. The combustion system is unmodified from that developed for natural gas fuelling. The results demonstrate that hydrogen can have a significant beneficial effect in reducing emissions without affecting efficiency or requiring significant engine modifications. Combustion stability is enhanced through the higher reactivity of the hydrogen, resulting in reduced emissions of unburned methane. The fuel’s lower carbon-energy ratio also reduces CO2 emissions. These results combine to significantly reduce tailpipe greenhouse gas (GHG) emissions. However, the effect on net GHG’s, including both tailpipe and fuel-production emissions, depends on the source of the hydrogen. Cleaner sources, such as electrolysis based on renewables and hydro-electric power, generate a significant net reduction in GHG emissions. Hydrogen generated by steam-methane reforming is essentially GHG neutral, while electrolysis using electricity from fossil-fuel power plants significantly increases net GHG emissions compared to conventional natural gas fuelling.Copyright

Comparison of injectors for compression ignition of natural gas with entrained diesel

New fuel injector prototypes for heavy-duty engines have been developed to use direct-injection natural gas with small amounts of entrained diesel as an ignition promoter. This ‘co-injection’ is different from other dual-fuel engine systems, where diesel and gas are introduced separately. Two co-injectors were compared with a Westport HPDI injector that injects diesel and gas through separate systems into the cylinder. All injectors have identical gas-nozzle geometry and inject fuel into the cylinder near top-dead-centre, but differ in the manner of introducing the diesel. Both co-injectors introduce diesel into the gas plenum before the gas needle is actuated, causing a two-phase gas-blast injection. The first co-injector (‘B’) injects the diesel with relatively high velocity into the gas plenum, which probably disperses it over a large volume inside the injector. The second prototype (‘CS’) introduces the diesel at very low velocity so that it may remain near the needle seat prior to injection. The injectors were tested in a 2.5-litre single-cylinder engine with 17:1 compression ratio. Load varied from 6 to 13 bar gross indicated mean effective pressure. Temperature-controlled exhaust-gas recirculation of 0 or 30 per cent was used. Co-injection of natural gas and diesel can increase the ignition delay relative to the HPDI system (which uses a pure diesel pilot injection). The HPDI and CS injectors required 7–15 per cent diesel fuelling (by energy), while B required 9 to 20 per cent diesel fuelling. All injectors yielded the same fuel economy (within 2 per cent). However, premixed diesel, gas, and air can burn rapidly enough to produce knock. Knock was typically inaudible (below 3 bar intensity) and greatly reduced for conditions with exhaust-gas recirculation. With co-injector CS, all gaseous emissions could be brought very close to those of the HDPIJ36 injector, but co-injector B resulted in high hydrocarbon and CO emissions at low load. Particulate emissions from the co-injectors were slightly lower than for the J36 injector, possibly due to more fuel/air premixing prior to ignition.

Compression ignition of directly injected natural gas with entrained diesel

Abstract A new fuel injector prototype for heavy-duty engines has been developed to use direct-injection natural gas with small amounts of entrained diesel as an ignition promoter. This ‘co-injection’ is quite different from other dual-fuel engine systems where diesel and gas are introduced separately. In an engine with co-injection, diesel and gas are injected simultaneously through one set of nozzle holes as the piston approaches top dead centre. Most of the combustion is non-premixed, as in a conventional diesel engine, but the natural gas supplies over 90 per cent of the energy for typical operating conditions. Reliable compression-ignition can be attained, but two injections per engine cycle are often needed to minimize engine knock. The present paper focuses on 800 r/min light-load operation (equivalence ratio between 0.05 and 0.22) with a single injection per cycle, in order to better understand how the ignition process is affected by in-cylinder conditions and the gas/diesel ratio. Two techniques were used to explore the data: response surface methodology and power-law fits. These methods both showed above a certain diesel/gas ratio that ignition delay approached that of pure diesel injections, but significant knock would occur if the total fuel energy of the injection was high. With high injection pressure and low cylinder pressure, the region of allowable diesel flow (i.e. the region with low knock intensity and high combustion efficiency) was increased for cases with low to moderate gas flow compared with low injection pressure. Injection pressure had little effect at high cylinder pressure, and had no significant effect on ignition delay.

The Effects of High-Pressure Injection on a Compression-Ignition, Direct Injection of Natural Gas Engine

The use of pilot-ignited, direct-injected natural gas fuelling for heavy-duty on-road applications has been shown to substantially reduce NOx and particulate matter emissions. The fuelling process involves the injection of pilot diesel near top-dead-center, followed shortly afterwards by the injection of natural gas at high pressure. The injection pressure of the gas and diesel will substantially affect the penetration of the fuel into the combustion chamber, the break-up and atomization of the diesel spray, and the mixing and nature of the turbulent gas jet. To investigate these influences, a series of experiments were performed on a single-cylinder heavy-duty engine over a range of engine operating conditions (exhaust gas recirculation fraction, engine speed, engine load). Due to the unique nature of the single-cylinder engine, it was possible to hold all other parameters constant while only varying injection pressure. The results indicated that injection pressure had a substantial impact on emissions and performance at high loads, where substantial reductions in PM and CO were observed, with only minor increases in NOx and no significant effect on tHC or fuel consumption. At low loads, no significant impact on either emissions or performance was detected. The effects of injection pressure, while still significant, were found to be reduced at increased engine speeds. Higher injection pressures were found to consistently reduce both the number density and the size of particles in the exhaust stream.Copyright