Gordon P McTaggart-Cowan

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

This study investigated the effects of injection pressure on the performance and emissions of a pilot-ignited, late-cycle direct-injected natural gas fueled heavy-duty engine. The experiments, conducted on a single-cylinder engine, covered a wide range of engine speeds, loads, and exhaust gas recirculation fractions. The injection pressure was varied at each operating condition while all other parameters were held constant. At high loads, increasing the injection pressure substantially reduced particulate matter and CO emissions, with small increases in NOx and no significant effect on hydrocarbon emissions or fuel consumption. At low loads, injection pressure had no significant impact on either emissions or performance. At high loads, higher injection pressures consistently reduced both the number density and the size of particles in the exhaust stream. Injection pressure had reduced effects at increased engine speeds.

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.

The Effects of Exhaust Back Pressure on Conventional and Low-Temperature Diesel Combustion

Modern diesel engines are seeing increasing system and after-treatment complexity which can lead to significant increases in the exhaust back pressure (EBP). This increases the amount of trapped residuals, raising the charge temperature but reducing the oxygen concentration. In this work, these effects of the EBP on diesel engine performance and emissions under conventional and low-temperature diesel combustion (LTC) regimes were investigated. Increasing the EBP resulted in higher pumping work for both combustion modes. While for conventional diesel combustion the effect of the EBP on combustion and emissions were not significant, for LTC the higher back pressures influenced the combustion and emissions formation processes. At low-load conditions, the increase in the charge temperature advanced combustion; at intermediate-load conditions, the reduction in the oxygen concentration delayed it. Smoke emissions were significantly reduced by a higher back pressure at intermediate-load conditions.

The effects of split injections on high exhaust gas recirculation low-temperature diesel engine combustion

Diesel engine emissions of oxides of nitrogen and smoke can be reduced simultaneously through the use of high levels of exhaust gas recirculation to achieve low-temperature combustion. However, single fuel injection per cycle diesel low-temperature combustion is also characterized by high fuel consumption and high total unburned hydrocarbons and carbon monoxide emissions. This work focuses on investigating the potential of a split (50/50) main fuel-injection strategy to reduce smoke, total unburned hydrocarbons and carbon monoxide emissions at exhaust gas recirculation levels lower than those required to achieve single-injection diesel low-temperature combustion at a medium-load, medium-speed operating condition. Experiments were performed on a 0.51 l single-cylinder high-speed direct-injection diesel engine running at 1500 r/min at an operating condition corresponding to a gross indicated mean effective pressure of 500 kPa. At this load, exhaust gas recirculation levels of 62% are needed to realize near-zero nitrogen oxide and smoke emissions, but this leads to an unacceptable reduction in thermal efficiency as well as high total unburned hydrocarbons and carbon monoxide emissions. This work compares the effects of split fuel injections at an exhaust gas recirculation level of 52% by volume to those from single injections at exhaust gas recirculation levels of 52% and 62%. The results demonstrate that the combined effects of exhaust gas recirculation rate and split injections can achieve near-zero nitrogen oxide with good thermal efficiency and total unburned hydrocarbons and carbon monoxide emissions much lower than at 62% exhaust gas recirculation. Single injection at this point results in excessive smoke, which can be reduced by over 75% through the split-injection strategy. These results are particularly relevant as they demonstrate very low nitrogen oxide emissions from an engine operation with acceptable thermal efficiency and at practical exhaust gas recirculation levels.

Effects of Hydrogen Addition on High-Pressure Nonpremixed Natural Gas Combustion

The effects of hydrogen addition on the ignition and combustion of a high-pressure methane jet in a quiescent charge of high-temperature, medium-pressure air were investigated numerically and experimentally. Subsequently, the results of these two fundamental studies were applied to the interpretation of combustion and emissions measurements from a pilot-ignited natural gas engine fueled with similar fuels. Whereas, under quiescent conditions, the influence of hydrogen addition on the autoignition delay time of the gaseous jet was small, a markedly greater effect was observed in the more complex environment of the research engine. Similarly, in the two fundamental studies, the addition of hydrogen to the methane fuel resulted in a reduction of NOx emissions, whereas increased levels of NOx emissions were observed from the engine, highlighting the difference between the autoignition and pilot-ignition process.

Effects of Fuel Composition on High-Pressure Non-Premixed Natural Gas Combustion

The effects of adding ethane or nitrogen on the ignition and combustion of a non-premixed high-pressure methane-air jet have been investigated using fundamental studies in a shock tube and advanced computational modeling. The results are then used to interpret the performance of a pilot-ignited natural gas engine fueled with similar fuels. The results show that the influence of the additives on the gaseous jet ignition process is relatively small, but that they have a greater effect on the research engine, where both fuels have similar influences on the spatial relationship between the gaseous jet and the pilot flame.

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

Effects of engine operating parameters on diesel low-temperature combustion with split fuel injection

This paper shows that a split-fuel-injection strategy can achieve robust, near-zero smoke and nitrogen oxide emissions at reduced exhaust gas recirculation levels under low-temperature combustion conditions. The overall objective of the work was to investigate the sensitivity (in terms of the engine emissions and the fuel economy) of a 50:50 (by mass) split-injection strategy to variations in the key engine operating parameters. Experiments were performed at operating conditions corresponding to a gross indicated mean effective pressure of 500 kPa at an engine speed of 1500 r/min in a 0.51 l single-cylinder high-speed direct-injection diesel engine. The paper presents the effects of different relative fuel injection timings at a variable intake oxygen mass fraction (10.5% and 12%) at a constant intake pressure (120 kPa, absolute) on the smoke, total hydrocarbon and carbon monoxide emissions with the split-main-injection strategy. The effects of a variable fuel injection pressure (90 MPa and 110 MPa) on diesel low-temperature combustion with split injection are also reported, as are the effect of an increased intake pressure (150 kPa, absolute). The combined effects of the operating parameters and the fuel injection timing on the smoke, nitrogen oxide, total hydrocarbon and carbon monoxide emissions and the gross indicated specific fuel consumption are described. For selected operating conditions, the cycle-resolved spray and combustion processes are visualized together with the flame temperature measurement using two-colour optical pyrometry to understand the combustion phenomena occurring in the split-injection strategy. The results of the optical studies show that different low-temperature combustion operating conditions producing similarly low levels of ‘engine-out’ smoke emissions have substantially different histories of soot formation and soot oxidation. An increase in the intake oxygen mass fraction reduced the total hydrocarbon emissions and the gross indicated specific fuel consumption at a given intake pressure, while a higher intake pressure reduced them further. Although significant soot formation took place from the second injection event, the majority of the soot was subsequently oxidized because of a slightly higher flame temperature and slightly higher oxygen concentration than in single-injection high-exhaust-gas-recirculation low-temperature combustion. A higher injection pressure did not have any significant effect on the emissions and the gross indicated specific fuel consumption.

Experimental Investigation of Low Temperature Diesel Combustion Processes

The work presented in this article investigates the three distinct phases of low temperature diesel combustion (LTC). Diesel LTC followed a cool flame–negative temperature coefficient (NTC)–high temperature thermal reaction (main combustion) process. The in-cylinder parameters, such as the charge temperature, pressure, and composition, had noticeable influences on these combustion stages. The NTC was strongly temperature-dependent, with higher temperatures inducing both an earlier onset of NTC and a more rapid transition from NTC to the main combustion process. An increase in the intake charge temperature led to an earlier occurrence of NTC and a reduction in the heat released during the cool flame regime. A higher fuel injection pressure improved fuel mixing and enhanced the low temperature (pre-combustion) reactions, which in turn led to an earlier appearance of the cool flame regime and more heat release during this phase. This increased the charge temperature and led to earlier onset of the NTC regime. A higher exhaust gas recirculation (EGR) rate reduced the intake charge oxygen concentration and limited the low temperature reaction rates. This reduced the heat release rate during cool flame reaction phase, leading to a slower increase in charge temperature and a longer duration of the NTC regime. This increased the ignition delay for the main combustion event. The injection timing showed a less significant influence on the cool flame reaction rates and NTC phase compared to the other parameters. However, it had a significant influence on the main combustion heat release process in terms of phasing and peak heat release rate.

Measurement of Residual Gas Fraction in a Single Cylinder HSDI Diesel Engine through Skip-firing

This paper proposes a method of determining residual gas fraction (RGF) by sampling the CO 2 concentration in the exhaust manifold of a single cylinder HSDI diesel engine. During a skip-fire event, the CO 2 concentration in the exhaust gas for the last firing cycle and the subsequent motoring cycle were measured using a fast-response emissions analyzer. The ratios of these two values are shown to be indicative of the RGF. To simulate the increase in exhaust pressure found with EGR or aftertreatment systems, the exhaust back pressure was elevated using an exhaust throttle. The intake pressure was held constant over a range of engine speed and load conditions. The results demonstrate that the RGF increases linearly with increasing exhaust back pressures for all engine operating conditions. The backflow of exhaust gas into the cylinder and intake manifold during the valve overlap period is found to be the most significant cause of the higher RGFs, especially at higher exhaust back pressures. The measured RGFs are used to validate the results obtained from a commercial 1-D engine flow simulation package. Analysis of the experimental in-cylinder pressure shows the effects of the residual gas on the combustion. With increased RGF, the ignition delay is reduced due to the higher endof-compression temperature caused by the hot residual gases. The offsetting effects of charge dilution on ignition delay are insignificant since the RGF never exceeds 9% of the charge. Pumping losses increase linearly with increasing exhaust back-pressure, reducing net indicated thermal efficiency. However, the gross indicated thermal efficiency is not significantly influenced by exhaust throttling.