Efficiency, Emissions Focus For CV Engine Development

Written by  Sameer Kumar | 14 March 2017 | Published in March 2017 ( Technology )

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With sales of around 60,000 units per month (LCVs + M/HCVs), the commercial vehicles segment is an important element in powering the Indian economy. It's also important for the segment to keep abreast of the latest global advances in commercial vehicle technologies, since improved engine efficiency and lower fuel consumption are critical for better profitability, while reduced emissions helps the environment in a big way. Here, we take a look at some of the newer developments in CV engine technology that promise a better future for commercial vehicle owners and operators.

THE NEED FOR IMPROVED EFFICIENCY

According to a study conducted by the Department of Energy (DOE) in the US, most diesel-powered commercial vehicle engines are only moderately efficient, with brake thermal efficiency (BTE) peaking at about 42 %, which means that these engines are converting only about 42 % of the fuel that they consume into actual mechanical output. This is partly due to thermodynamic limitations of some heavy-duty diesel engines and CV manufacturers have been studying the possibilities of making changes to basic engine architecture and using NOx aftertreatment systems for improved efficiency. Also being used and evaluated are factors like higher / variable compression ratios, reduced internal friction, developments in variable-geometry turbochargers (as well as the use of multiple turbos), more advanced high-pressure common-rail fuel-injection technology for improved fuel combustion, turbocompunding processes for better exhaust heat recovery systems, urea-based selective catalytic reduction for better emissions compliance, biofuel blends (not used in India though) and on-board diagnostics systems that allow technicians to keep track of an engine's state of operations. In all of this, weight, packaging constraints, development and production costs, reliability and durability are also important factors, what with CV engines expected to last 15-20 lakh kilometres or more.

CV engines typically operate at lower speeds and high or very high load conditions, and manufacturers are these days aiming to improve BTE to 50-55 %, which is a challenge in terms of deploying the technology required for this improvement. With newer engine architecture and with better heat recovery systems, CV manufacturers have been able to achieve modest improvements in low-temperature combustion, resulting in BTE numbers that are higher than what was prevalent a decade or more ago, but 55 % will require still more work.

CV manufacturers have also been studying the use of alternative materials for producing engines that are lighter and more fuel efficient, with compromising their longevity. Alternative materials (aluminium and other metal alloys) have been considered for engine components like cylinder blocks, heads and liners, pistons, camshafts, crankshafts and bearings. Other areas of R&D are better fuel-injection systems that are more stable and erosion resistant, valve train that has lower reciprocating mass and greater wear resistance, exhaust gas recirculation (EGR) systems built with corrosion-resistant materials, stronger, more creep-resistant materials for turbocharger components, and lighter, corrosion-resistant materials for exhaust systems.

Why the need for newer materials? Well, one example is cast iron cylinder heads and engine blocks used in CV engines, which can be tested to the limits of their tensile strength by modern high-pressure common-rail FI systems that operate at peak cylinder pressures of 190-260 bar. Yes, higher pressures can equate with improved efficiency, but tensile strength will need to keep up, for which manufacturers will need to work with advanced metal alloys that might also be prohibitively expensive to use. Going forward, the challenges will only intensify, since CVs will ultimately have to meet 'enhanced environmentally friendly vehicle' (EEV) or equivalent norms, where emissions limits are even stricter than those specified in Euro V norms.

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THE CHALLENGES AHEAD

With upcoming Euro VI emissions norms in the not-too-distant future, and with CV operators demanding continuously improving fuel efficiency, CV manufacturers will be forced to innovate when it comes to building engines. While the basic 8-cylinder configuration used in most HCVs is likely to remain unchanged, there will definitely be advances in fuel injection systems that are more precise and operate at higher pressures. In fact, the pump-nozzle and pump-line-nozzle systems still in use on many CVs are likely to disappear completely, and will be entirely replaced with common-rail injection systems that will work at pressures of up to 2100-2500 bar and, with hydraulic intensifiers, maybe even up to 3000 bar. With this increased pressure will come the need for tighter manufacturing tolerances and new cylinder head materials with much greater tensile strength.

Given the need for better fuel economy, CV manufacturers may also need to go down the path of cylinder deactivation technology (for low load operating conditions), or engine downsizing, in the future. However, since CV engines will still need to operate in high load conditions, manufacturers will need to increase specific output if engine size reduces, which will require better forced induction (supercharging / turbocharging) systems and higher exhaust gas recirculation (EGR) rates, along with wider adoption of urea-based selective catalytic reduction (SCR) or diesel particulate filter (DPF) for emissions control.

Another promising development for CV manufacturers might be homogeneous charge compression ignition (HCCI), a high-efficiency clean-burn technology in which the air-fuel mixture is compressed to the point of spontaneous combustion. Benefits of HCCI include significantly improved fuel economy and inherently low levels of harmful emissions (both NOx and particulate matter), potentially eliminating the need for exhaust aftertreatment systems like catalytic converters. The technology is still under development, with R&D inputs from various OEMs, and the benefits should hopefully start trickling down to production-ready vehicles within the next few years.

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BEYOND THE IC ENGINE

Even though it's about 125 years old, the diesel engine is still going strong and according to various global estimates, will still be powering more than 90 % of all L/M/HCVs even 20 years from now. However, increasingly stringent emissions norms and ever higher requirements of fuel economy will ultimately, at some point, lead to the gradual demise of the mighty diesel and CV manufacturers will have to look at hybrid and electric powertrains. It's a future for which tentative preparations are already underway. In fact, buses with hybrid and/or electric powertrains are already running successfully in various countries (soon, including India, though in a very limited way), though developing similar powerplants for heavy commercial vehicles may be much more challenging, due to their requirements of very long range and very heavy load carrying capacity.

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While we still seem to be some years away from electric motors and batteries that are robust enough to power commercial vehicles, OEMs like MAN and Volvo are working on hybrids, while Mercedes-Benz, Tesla and some others have already started development work on full electric trucks, which are expected to go into production in the next 5-10 years. Benefits, of course, include zero emissions, reduced NVH, superior torque delivery and reduced running costs.

Going forward, whether diesel-powered or hybrid-electric, commercial vehicle powerplants will continue to evolve, become more energy efficient and will be far more environment-friendly in the future.

TEXT: Sameer Kumar

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