Diesel engine developments
Cummins engines – planning for the long haul1 November 2009
Engine and genset maker Cummins is undertaking a major overhaul of its offerings in readiness for the onset of Tier 4 and Stage 3 legislation due to start taking effect in January 2011. Several of the resulting upgrades have been released this year, and a further tranche of modifications will be applied in 2010.
American manufacturer Cummins has been making diesel gensets since the 1920s. In the intervening ninety years it has developd its product range to include units powered by gas and ‘altenative’ fuels and claims now to be the only operator in the market that makes all its own components. Its generator technology, for instance, comes largely from its 1986 acquisition of Newage.
Advances in genset design since the 1990’s have been led by increasingly demanding US and European legislation of toxic gases and particulates emissions with their Tier and Stage programmes, and are therefore the story largely of diesel engine design, which has been led by the US and applied first to highway truck engines and then to off-highway engines. These latter are mostly found powering constant speed gensets for stationary power – for stand by, prime and temporary site power – variable speed industrial engines and in boats of various kinds. The size of the American market has ensured that the major European manufacturers have at least kept pace with US manufacturers in terms of technological progress.
Evolution of emissions standards
Emissions controls for internal combustion engines were first introduced in 1959 when the state of California applied them to passenger cars. This was followed in 1968 by US federal legislation. Dramatic reductions were achieved over the next decades, then in 1988 heavy duty trucks were included. Europe folowed suit in 1988 when it introduced its first heavy duty truck legislation. Non-road (including mobile gensets) engines were included in 1996 in the USA and Europe added legislation to cover non-road machines in 1999 but did not include constant speed engines until 2006. A major difference between US and EU standards is that the former cover engines of all sizes except ‘hobby engines’ while latter do not yet cover any machines above 560 kW in size.
However there is an intention and a trend towards the unification of all engine standards applied in the USA and Europe by around 2020, a date beyond the current programme. It is likely that legislation in other parts of the world will follow at a short distance.
Limits from the current US (Tier) and EU (Stage) limits for engines and gensets are shown in Tables 1 and 2 and in Figures 4 and 5. Figure 5 shows the demanding standards set by NOx legislation and illustrates the price in combustion efficiency that it exacts. Because of the temperature at which nitrogen oxides form in the combustion process it is relatively easy to create a low NOx burn. The challenge is to create it without loss of thermal (ie fuel) efficiency and the best that motor makers have been able to achieve in this direction is to stand still – that is, zero or very marginal increases in fuel efficiency.
The standard for any given engine and the date of its implementation depend on size, type of usage (road vehicle, boat, traction, non-road, (mobile and stationary)) variable or constant speed, and whether or not newly type-tested. The tables and charts shown here refer to type-tested variable speed (and some constant speed) non-road engines, and the specific genset regulations due to start taking effect in 2011under Tier 4.
Stage 3 having started implementation in 2006 and 2007, manufacturers are now looking towards Tier 4 ‘Interim’, which starts up in 2010 and is implemented in stages and by category to 2017 when Tier 4 Final kicks in. This stage will represent the toughest standards that can be achieved with current technology. Cummins is committed to invest $329 million into expanding its business and improving its technology around the world in the next few years, a mission based on several mantras: to meet or exceed legislation requirements; to lower noise levels as well as exhaust emissions; and to reduce the total cost of ownership. Driving it are (mainly) the US and EU legislative steps taking effect between 2011 and 2017, and the introduction of tougher noise regulations.
During 2009 the company has introduced new sub-55 kVA products, noise level reduction up to 6 dB on some products (77 dB at 1m to 71 to 74 dB), new 150-220 kVA products, emission compliance to Stage IIIA, power density increases across the range and improved control systems. The standout features are the incorporation of excitation boost systems (EBS) and modular common rail systems, the introduction of a 1250 kVA (1 MW) prime power 20 foot standard container unit for the rental and construction market and the implementation of new ‘Powerstart’ and ‘Powercommand’ controls across the range.
Cummins’ ambitions for next year include upgrading half the product range, introducing new products now in development from 1250 kVA to 3000 kVA and new low emissions products introduction up to 2500 kVA with modular common rail systems.
Developments in 2009
In January Cummins introduced a modified version of its QSL9 engine platform ready to meet the EPA Tier 4 Interim and EU Stage IIIB off-highway emissions standards due for implementation in 2011 (Figure 1). Ultimately it will replace the 8.3 litre QSC range. The primary mechanism was the incorporation of a fully integrated air-intake to exhaust aftertreatment system with all the Tier 4 technology enablers designed and manufactured by Cummins themselves. The resulting cleaner, more efficient combustion reduced QSL9 fuel consumption by up to 5 %, dependent on rating, and increased high-rate power to 380 hp (283 kW) with peak power rising to 400 hp (298 kW) at a lower rpm in response to very high work load demands. The corresponding figures for the Tier 3 version are 272 kW and 280 kW.
The 8.9-litre Tier 4 platform also incorporated the company’s XPI extra-high pressure injection system, the latest development of common rail capability. This enables multiple injection events with very high fuel injection pressure across all engine rpm speeds, resulting in cleaner combustion and improved engine response. The fuel system was complemented with a variable geometry turbocharger with a sliding-nozzle design, also by Cummins. This continuously varies the airflow boost to precisely match engine rpm and load demands. The whole efect is also to broaden the output range to 179-298 kW.
The QSL9 utilises the same Tier 4 emissions architecture as previously announced for the smaller QSB6.7 and larger QSX engine (Figures 3 and 6). An integrated Cummins particulate filter enables a 90 % reduction in particulate matter and a cooled exhaust gas recirculation system reduces oxides of nitrogen by 45 %. The particulate filter replaces the exhaust silencer with equivalent sound reduction and is a rugged design hardened to withstand severe shock loads and vibration.
In April this same Tier 4 emissions technology architecture was extended to the company’s 4-cylinder QSB3.3 and QSB4.5 engines to meet EU Stage IIIB and US EPA Tier 4 Interim off-highway emissions in 2012 across a 56 to 119 kW power range.
Both the cooled-EGR system and the particulate aftertreatment unit have been specifically developed for the 4-cylinder platforms as a more compact and simplified version of the Tier 4 Interim technology previously applied to the 6-cylinder QSB6.7 engine (Figure 2). The high pressure common rail (HPCR) fuel system employed on the Tier 3 QSB3.3 and QSB4.5 is already capable for Tier 4 Interim and will require no major change. An upgraded turbocharger with electronic control will be utilized to manage EGR flow across the entire engine rpm range.
QSB3.3 ratings extend from 75 to 110 hp (56 to 82 kW) for Tier 4 Interim, retaining the best-in-class power output for an engine of this size. The QSB4.5 occupies the 110- to 160 hp (82 to 119 kW) power band and is claimed to offer the same, or improved, torque delivery as the Tier 3 engine. Cleaner and more efficient combustion improves fuel efficiency by up to 5 % compared to Tier 3, depending on rating and installation optimisation.
The 4-cylinder development programme for Tier 4 Interim was driven by the need to avoid the complexity of increasing displacement or overloading the engines with complications such as dual turbochargers.
The 4-cylinder QSB3.3 and QSB4.5 now join the 6-cylinder QSB6.7 to complete the QSB lineup ready for Stage IIIB and Tier 4 Interim.