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Natural gas is a challenging fuel for HCCI engines because its single-stage ignition and rapid combustion make it difficult to optimize combustion timing over a significant load range. This study investigates direct injection of a pilot quantity of high-cetane fuel near TDC as a range extension and combustion control mechanism for natural gas HCCI engines. The EGR and load range is studied in a supercharged natural gas HCCI engine equipped with external EGR, intake heating and a direct injection system for n-heptane pilot fuel. The operating range and emissions are of primary interest and are compared between both the baseline HCCI engine with variable intake temperature and the direct injected HCCI (DI-HCCI) engine with constant intake temperature. Test results show the EGR and load range at fixed intake temperature can be extended using pilot direct injection.

Because of domestic production from renewable sources and their clean burning nature, alcohols, especially ethanol, have seen growing use as a blending agent and replacement for basic hydrocarbons in gasoline. The increasing use of alcohol in fuels raises questions on the safety of these fuels under certain non-operational situations. Modern vehicles use evaporative emission control systems to minimize environmental emissions of fuel. These systems must be relatively leak-free to function properly and are self-diagnosed by the vehicle On-Board Diagnostic system. When service is required, the service leak testing procedures may involve forcing test gases into the “evap” system and also exposure of the fuel vapors normally contained in the system to atmosphere. Previous work has discussed the hazards involved when performing shop leak testing activities for vehicles fuelled with conventional hydrocarbon gasoline [1, 2].

At certain operating conditions, Homogeneous Charge Compression Ignition (HCCI) can provide ultra-low NOx emissions with good combustion efficiency. However, using HCCI operating modes in a SI-based engine still requires some means to control HCCI ignition over a range of operating conditions. Amongst various possible control techniques, altering fuel ignition quality by blending a reformer gas mixture with base fuel is attractive, primarily because of the capability to alter fuel injection ratios on a cycle-by-cycle basis. As well as fuel blending, the mixture composition is defined by equivalence ratio (ϕ) and exhaust gas recirculation (EGR) ratio. The effects of changing such parameters have been widely studied both experimentally and with models. However, adjusting any variable has multiple effects on the mixture's thermodynamic and chemical properties so a detailed understanding of how these variables affect combustion is generally difficult to achieve.

Because of the potential for low NOx emissions with high efficiency, HCCI engines could develop a significant niche in the engine world. However, HCCI engines suffer from a narrow operating range between knock and misfire boundaries because the ignition timing is only controlled by mixture chemistry and compression conditions. Varying combinations of operating parameters are required to obtain good combustion under different conditions and chemical kinetic models are widely used as an engine research tool. The performance of such models depends critically on the accuracy of the chemical mechanisms which are still under development and require some optimization, particularly for larger hydrocarbon molecules. This study starts with a Chalmers University mechanism [1] which is well-proven for pure n-heptane but works less well for mixtures blended with significant amounts of reformer gas containing high fractions of H2 and CO [2].

Although HCCI engines promise low NOx emissions with high efficiency, they suffer from a narrow operating range between knock and misfire because they lack a direct means of controlling combustion timing. A series of previous studies showed that reformer gas, (RG, defined as a mixture of light gases dominated by hydrogen and carbon monoxide), can be used to control combustion timing without changing mixture dilution, (λ or EGR) which control engine load. The effect of RG blending on combustion timing was found to be mainly related to the difference in auto-ignition characteristics between the RG and base fuel. The practical effectiveness of RG depends on local production using a fuel processor that consumes the same base fuel as the engine and efficiently produces high-hydrogen RG as a blending additive.

Given the advantages of ultra low NOx emission and high thermal efficiency at part load, HCCI engines might develop a significant niche in the engine world, provided that a suitable HCCI combustion control mechanism can be found. The problem is that HCCI occurs in a narrow operating range bounded by severe knock and misfire limits. Acceptable combustion behavior can be lost due to minor changes in speed, load, temperature or other variables. One approach to control HCCI combustion is to use a variable blend of base fuel and reformed fuel which can be adjusted on a cycle-by-cycle basis to control the combustion behaviour. Developing this control technique requires researchers to be able to optimize the settings and predict the effects of the many variables that affect HCCI ignition and combustion.

Homogeneous Charge Compression Ignition (HCCI) engines offer high fuel efficiency and some emissions benefits. However, it is difficult to control and stabilize combustion over a sufficient operating range because the critical compression ratio and intake temperature at which HCCI combustion can be achieved varies with operating conditions such as speed and load as well as with fuel octane number. Replacing part of the base fuel with reformer gas, (which can be produced from the base hydrocarbon fuel), alters HCCI combustion characteristics in varying ways depending on the replacement fraction and the base fuel auto-ignition characteristics. Injecting a blend of reformer gas and base fuel offers a potential HCCI combustion control mechanism because fuel injection quantities and ratios can be altered on a cycle-by-cycle basis.

Homogeneous Charge Compression Ignition (HCCI) combustion offers high fuel efficiency and some emissions benefits. However, it is difficult to control and stabilize combustion over a significant operating range because the critical compression ratio and intake temperature at which HCCI combustion can be achieved vary with operating conditions such as speed and load as well as with fuel octane number. Replacing part of the base fuel with reformer gas, (which can be produced from the base hydrocarbon fuel), alters HCCI combustion characteristics in varying ways depending on the replacement fraction and the base fuel auto-ignition characteristics. Because fuel injection quantities and ratios can be altered on a cycle-by-cycle basis during operation, injecting a variable blend of reformer gas and base fuel offers a potential HCCI combustion control mechanism.

Combustion in Homogeneous Charge Compression Ignition (HCCI) engines is the subject of intensive combustion modeling efforts because, while they have potential for low fuel consumption and emissions, they also suffer from problems of combustion control. Modeling studies are being used to predict the effects of changing controllable parameters and to ‘measure’ important combustion-related phenomena which can not be observed directly. A significant limitation of most current combustion models is that they still rely on arbitrarily adjusting initial conditions, (especially temperature) in order to match experimental results. This limits the confidence with which models can be used to predict HCCI combustion behavior over any range of conditions wider than available experimental data. This paper describes a new method to solve the initial condition problems for HCCI combustion modeling based on simulated heat transfer between intake and residual components.

Despite progressive implementation of stringent emission regulations, vehicle tailpipe emissions remain the major source of air pollution problems in most urban areas. To control and reduce tailpipe pollutants, it is critical to understand in-use emissions as a basis for any future emission controls. At present, emission factors are mainly studied by chassis dynamometer methods. However, concerns have been raised about the extent to which emissions produced by on-road vehicles can be predicted using emission factors developed based on standardized dynamometer test procedures. This paper describes an on-board, in-use vehicle emissions measurement system which measures tailpipe emission rates while the vehicle is in real service experiencing complex traffic conditions, driver behavior and weather.

Motorized transport has become an essential part of our world economic system with an ever-increasing number of vehicles on the road. However, considering the depletion of energy resources and the aggravation of greenhouse gas issues, it is critical to improve vehicle fuel consumption. These demands are moving us toward advanced engine and powertrain technologies. However, understanding our progress also requires improvements in the way we measure and certify vehicle emissions and fuel economy performance. This paper describes the use of an on-board fuel consumption and emissions measurement system to develop on-road fuel consumption functions that can be used to quantify the fuel economy impact of vehicle, road and traffic control changes. The system uses an ECM OBD-II scanner, a Mass Air Flow meter and an emissions analyzer to monitor fuel consumption and exhaust CO2 emission rates (in g/s) as well as vehicle speed and other parameters.

This paper describes use of reformer gas (RG) to alter and control combustion in a CNG-fueled HCCI engine. Experimental work used a mixture of simulated RG (75% H2 and 25% CO) to supplement base CNG fueling in a CFR engine upgraded to achieve high compression ratios. RG was used to improve the engine's operating performance and to control combustion onset in experiments conducted at three different compression ratios. A combination of high compression ratio (18.5) and high intake temperature (140°C) was observed to be appropriate to run the CNG-fueled CFR engine in HCCI mode. RG replacement of CNG altered combustion characteristics and expanded the operating range on the lean side. Use of RG decreased knock severity and reduced NOx emission. At constant relative air/fuel ratio (λ) it advanced combustion timing, moving the maximum cylinder pressure earlier in the cycle and increasing maximum pressure.

Flame stretch arises due to strain and change in flame curvature and is extremely important in spark ignition (SI) engine combustion. It can significantly alter the flame speed and hence, the burning duration. This, in turn, can have serious influence on engine performance and exhaust emission. A good understanding of stretch effect can thus lead to improved fuel efficiency, reduced cyclic variations, and better emission control for SI engines. In this study, we analyzed initial temperature and pressure effects on the stretched flame speed of a laminar, premixed, freely propagating, spherical methane-air flame in accordance with the Markstein theory, which postulates a linear relationship between stretched and unstretched flame speed. The unstretched flame speed was computed using CHEMKIN GUI 4.0.1 with GRI Mech 3.0 reaction mechanism. Analytical expressions relating stretched and unstretched flame speed were employed to derive the stretched flame speed.

There are many possible applications for the discrete acoustic wave and phase detection (DAWPD) sound speed sensor. The DAWPD sensor is a compact sensor that measures the sound speed of gases. The sound speed of gaseous fuels can be related to various properties of a fuel including composition. A sound speed sensor can be used as a fuel quality sensor in natural gas vehicles (NGVs), variable gaseous fuel (VGF) vehicles (a VGF vehicle uses a mixture of hydrogen and natural gas fuel), and proton exchange membrane (PEM) fuel cell vehicles (FCVs). In a NGV the DAWPD sensor can be used to measure the methane number, Wobbe number, and hydrogen-to-carbon ratio of the natural gas. The DAWPD sensor can also be used to find the composition of the fuel used in VGF vehicles. In PEM fuel cell vehicles small amounts of CO (>25 ppm) can poison the fuel cell. The DAWPD sensor can measure the amount of CO in the hydrogen fuel in order to control the fuel reforming process.

As a first step toward better understanding of the effects of flame stretch on combustion rate in SI engines, the burning velocity of a premixed, spherical, laminar methane-air flame propagating freely at standard temperature and pressure was investigated. The underlying un-stretched burning velocity was computed using CHEMKIN 3.7 with GRI mechanism, while the Lewis number and subsequently the Markstein length were deduced theoretically. The burning velocity of the freely growing flame ball was calculated from the un-stretched burning velocity with curvature and stretch effects accounted via the theoretically deduced Markstein length. For the positive Markstein length methane-air flame, flame stretching reduces the burning velocity. Therefore, the burning velocity of a spark-ignited flame starts with a value lower than, and increases asymptotically to, the underlying un-stretched burning velocity as the flame grows.

Biomass is regarded as a renewable resource for upgrading to solid or liquid fuels or for electricity generation. Because its energy density is very low compared to petroleum or coal, the cost of transporting biomass is a significant part of the total biomass cost. For this reason it is usually regarded as a local resource. However, appropriate logistic systems may allow collection of biomass over a large geographical area, thus making it possible to consider efficient, large scale energy conversion systems. For areas without significant water transportation, the basic choices are between truck-based, train-based and pipeline transportation. Previous work has shown that pipeline transport is not effective for biomass delivery due to uptake of carrier fluid (water or oil) by the biomass. Hence, the choice becomes one between train and truck transport.

Ammonia is a potential alternative fuel that was indeed put into use in Belgium in World War II due to the extreme shortage of diesel. It has a high heating value per unit volume (1.16 × 107 kJ/m3) and its combustion products can be as or more environment-friendly compared to conventional hydrocarbon fuels. This study examined the combustion characteristics of premixed ammonia-air mixtures at atmospheric and elevated conditions which are encountered in SI engine operation. The laminar burning velocity, flame temperature and species distribution were determined using the Lindstedt mechanism in CHEMKIN. A freely propagating flame was assumed to facilitate the investigation. The predicted laminar burning velocity and the flammability limits were compared with experimental values.

This paper demonstrates vehicle emission factor measurement using an on-board, on-road system and examines the effects of ambient temperature on those emission factors. Vehicle operating parameters, fuel consumption and emissions were measured on-road using a portable measurement system designed for ease of use with a range of vehicles, drivers and driving situations. The results reported here come from repeated trips over a 17.4 km urban / suburban route with a particular driver and vehicle. As such, the emission factors developed here do not represent the current on-road fleet. However, they show the strong influence of actual operating conditions (particularly ambient temperature) and of the vehicle control system's response to non-standard conditions. This leads to an appreciation for on-road testing as a means to illustrate vehicle emission behavior in real conditions and to highlight conditions which may require more detailed study.

Automotive tailpipe emissions are a significant contribution to urban air quality problems.(1) However, it is difficult to quantify the extent of that contribution and to quantify any progress in solving the problem. Emissions inventories are commonly based on vehicle registrations, assumed mileage and a set of emission factors. The emission factors are based on dynamometer testing of selected vehicles undertightly controlled conditions. Actual vehicle operation in any urban area encompasses a wider range of vehicles, operating conditions and ambient conditions. Given the highly tuned nature of current engine management systems, the actual in-use emissions levels can be highly sensitive to non-standard ambient and operating situations.(2,3,4,5) This paper describes an on-board system used to record ambient conditions, driving behavior, vehicle operating parameters, fuel consumption and exhaust emissions.

It is commonly stated that natural gas-fueled forklifts produce less emissions than propane-fueled forklifts. However, there is relatively little proof. This paper reports on a detailed comparative study at one plant in Edmonton, Canada where a fleet of forklift trucks is used for indoor material movement. (For convenience, the acronym NGV, ie. Natural Gas Vehicle is used to designate natural gas-fueled and LPG, ie. Liquified Petroleum Gas, is used to designate propane-fueled forklifts). Until recently the forklift trucks (of various ages) were LPG carburetted units with two-way catalytic converters. Prompted partially by worker health concerns, the forklifts were converted to fuel injected, closed-loop controlled NGV systems with three-way catalytic converters. The NGV-converted forklifts reduced emissions by 77% (NOX) and 76% (CO) when compared to just-tuned LPG forklifts.