By: Vahid Hosseini High Efficiency Clean Combustion (HECC) is the low temperature highly diluted combustion that is being looked at as the most recent type of combustion for internal combustion engine applications. HECC is majorly performed using two methods of premixed HECC and mixing controlled HECC. Premixed HECC is called Homogeneous Charge Compression Ignition (HCCI) combustion where a premixed air/fuel mixture is ignited by compression in the form of auto-ignition. The mixture is normally highly diluted with excess air and/or EGR producing low temperature flame-less combustion that results to low NOx emissions and high diesel-like efficiency. The HCCI combustion suffers from lack of direct method to control combustion timing. Mixing controlled HECC is performed in direct injection diesel engines by multiple injections with extremely high EGR level. Unless having high injection pressure and fine injector tip openings, achieving mixing controlled HECC is difficult. During my PhD studies at University of Alberta, I developed a new method to control HCCI combustion timing using partial reforming concept. Using a mixture of hydrogen and carbon monoxide it was found that reformer gas is capable of controlling combustion timing in a fuel with multi-stage auto-ignition property. In National Research Council (NRC) – Institute of Chemical Process and Environmental Technology (ICPET) I am trying to characterize different types of diesel fuels for HCCI combustion using a CFR engine. I work at understanding fuel chemistry effects on HCCI combustion using a port fuel injection fuel vaporizer on a range of diesel fuels, PCCI combustion by direct injection of fuels with common rail diesel fuel injection system, hydrogen and reformer gas enrichment of advanced combustion systems, and effects of biodiesel chemistry on conventional and advnaced diesel combustion. HCCI Combustion Homogenous Charge Compression Ignition (HCCI) combustion is defined as autoignition of a usually homogenous air/fuel mixture under extremely lean/diluted condition with excess air and/or exhaust gas recirculation (EGR). A homogenous mixture is inducted into the cylinder and autoignites by compression. HCCI is a combination of conventional spark ignition (SI, gasoline) engine (by having homogenous charge) and compression ignition (CI, diesel) engine (by being ignited by compression). Why is HCCI combustion attractive? Under controlled condition at highly diluted mixture HCCI combustion shows a higher thermal efficiency than conventional engines (because of highly diluted mixture and lower peak combustion temperature) and it produces almost no NOx emission without using a NOx reduction catalyst. This is definitely a break-through technology to achieve NOx-less combustion mainly considering 2010 emission regulatory standards. What’s wrong with HCCI that has not been implemented yet? Operating region in an HCCI engine is extremely limited to knock on one side and misfiring/partial burning on the other side. So HCCI is capable of running under part load condition and if medium to full power is required the engine has to switch back to normal SI or CI mode. Also, despite of having extremely low NOx production, unburned hydrocarbons and carbon monoxide emissions are high (which is by the way not that difficult to handle). The main important issue is that there is no direct control method to adjust HCCI combustion timing. In SI engine the park timing and in CI engine the injection timing are control mechanisms that effectively control combustion timing to get optimum torque and efficiency. In HCCI engine there are not such options available. Several indirect methods have been proposed such intake temperature adjustment, variable compression ratio, variable blend of fuel on a cycle-by-cycle basis, variable valve timing, etc. Reformer gas/ hydrogen enrichment of HCCI combustion During my PhD studies at University of Alberta, I explored the possibility of controlling HCCI combustion timing using reformer gas. Reformer is light gas mixture dominated by hydrogen and carbon monoxide and can be produced onboard using fuel reformer from any type of hydrocarbon using a catalytic reactor. Experimental results supported by modeling analyses confirmed that for fuels such as n-heptane with double-stage heat release characteristics, reformer gas effectively consumes free radicals between two stages of combustion and retards combustion timing toward an optimized value. It is less effective foe fuels with high octane number such as iso-octane. It also advances HCCI combustion timing of natural gas, creating the possibility of running a natural gas HCCI combustion engine with lower intake temperature. < xml="true" ns="urn:schemas-microsoft-com:office:office" prefix="o" namespace=""> Effect of fuel chemistry on HCCI combustion It is well-known that HCCI combustion characteristics are dominated by chemical kinetics. The chemistry of fuel plays an important role in combustion initiation and development. Octane or cetane numbers are widely used to describe the qualities of gasoline and diesel fuels. Apparently they cannot predict HCCI combustion precisely. I am trying to understand effects of diesel fuel chemistry specifically volatility, aromatic content, and cetane number on HCCI combustion. A large matrix of fuels with a range of properties is being examined. Some example of fuels are oil sands derived diesel fuels with various hydro processing severities, biodiesel, pure fuels such as n-heptane and iso-octane, and Fuels for Advanced Combustion Engines (FACE). The other aspect of this research is to find a solution for rating fuels for HCCI combustion to replace conventional octane and cetane number qualities. Reformer gas effect on diesel HCCI combustion Based on my PhD studies results, it seems that reformer gas is more effective on diesel-type fuels with low octane number and multi-stage autoignition behavior. Hence, I am examining effects of hydrogen on HCCI combustion of fuels with high cetane and low cetane qualities to verify the possibility of fuel reforming to operate a dual mode CI/HCCI engine using the same high cetane conventional diesel and convert it onboard to be used in HCCI mode. Common rail injection clean diesel combustion The project is continuation of HCCI project. In HCCI test cell, the fuel is vaporized and mixed inside the intake port. That creates the possibility of vaporizing various quantities of fuel in the port and keeps the rest of vaporization for compression stroke. Using another test cell equipped with a single cylinder high power diesel engine with electronically controlled common rail diesel injection system, the idea is to explore effects of fuel chemistry on clean diesel combustion (regular diesel with high EGR) and partially premixed HCCI (early injection). In this case, vaporization happens completely inside the cylinder.