Cummins uprates and aftercools with Super Ease
Page 52
Page 53
Page 54
If you've noticed an error in this article please click here to report it so we can fix it.
The break point for charge-cooling of its 14-litre engine is 300hp says Cummins and the four new Super E variants are its answer to those UK operators demanding more power. Tim Blakemore describes the latest 14-litre engines
THE FOUR "Super E" 14-litre engine variants, with gross power ratings ranging from 322-402hp, represent Cummins's response to the increasing demand in the UK for tractive unit engines with power ratings above 300hp.
In 1978 these engines accounted for less than seven per cent of tractive unit registrations. By 1982 that share had increased to 12 per cent, and last year, following the 38 tonnes C and U amendment, just over 24 per cent of tractive units registered had engines rated above 300hp.
Cummins regards the 300hp mark as the break point for chargecooling of its 14-litre engine to be worthwhile in terms of better fuel economy and reduced thermal loadings, which is why there are no plans to introduce a charge-cooled E290. But the 10-litre engine demands charge-cooling for an output of 290hp or above, in Cummins's view.
Apart from its air-to-water heat exchanger, the LTA10-290 is mechanically identical to the LT10-250, which was introduced in 1982 and described in CM October 9, 1982. But the Super E engines (or phase two NTE models as they are designated at Cummins) have a number of significant new features aimed at improving fuel economy, extending service intervals and reducing noise as well as providing two new ratings, at 320hp and 380hp gross. The existing aftercooled E Series range, which was introduced in 1978, is rated at 350, 370, and 400hp gross.
All Super E engines have the airto-water type of charge-cooler, integral with the inlet manifold which we have seen used before by Cummins on high-powered 14-litre variants such as the NTE 370, which was road tested in the Bedford TM, CM March 13 1982. (Cummins correctly refers to it as an aftercooler rather than the more common but usually incorrectly used "intercooler" -an intercooler cools the charge between two turbochargers when two stage turbocharging is used.)
The latest heat exchanger has been made more efficient by arranging its core so that the water now passes through it three times from end to end, rather than once, as before.
The effect of this has been to improve the aftercooler's efficiency from 70 per cent to 82 per cent, which means the inlet air's temperature can now be reduced by a further 11°C (20°F). Typically the intake air on the Super E320 will be at 177°C (350°F1 when it enters the heat exchanger and at 99°C (211°F) when it enters the inlet ports.
The Super E pistons retain the familiar, shallow inverted saucer shaped Cummins combustion chamber but minor dimensional changes have altered compression ratios slightly. The 320hp rated engine has a compression ratio of 15:1 compared to the E290's 15.3:1 while the 350, 380, and 400hp variants all use the same piston and have a compression ratio of 14:1.
Cummins's policy with the Super E320 is to maintain the same peak cylinder pressures as in the E290, so though the turbocharger boost pressure has gone up slightly, the injection timing has been retarded a little and the compression ratio has gone down, Retarding the injection timing has also helped Cummins to reduce engine noise by a little over 1 dB(AL for the Super E320 compared with the NTE 290 on a drive-by test.
The top ring on the Super E320's piston has been moved nearer the crown in order to reduce the amount of dead air in the compression space and thus improve specific fuel consumption. A similarly high mounted top ring is used on the 10-litre engine, Cummins's engineers are confident that the same principle could also be applied successfully to the 350, 380, and 400hp rated models but because of the rather higher cylinder temperatures of the higher power variants they decided to adopt a cautious approach and leave these pistons with the conventional lower top rings. The closer to the crown of the piston the top ring is, the higher the temperatures it has to contend with, The Super E engines have the same 63mm (2.5in) (Big Cam) camshaft journal diameter as E Series engines and the same injector cam profile, but the lift of the inlet and exhaust cam lobes has been increased by 20 per cent (from 0.5in to 0.6in) to improve the engine's breathing.
Some changes have been made to the latest Cummins injector in the interests of longer service life and resistance to erosion. The fuel-feed orifice has been raised in the injector body to put it in a cooler place. This should help to prevent the formation of carbon inside the injector, which used to tend to happen on engines with duty cycles which included a lot of closed throttle work.
The OFF (direct feed flow) injector of the Super E engines also has a chromium-plated plunger to help resist erosion. OFF injectors are interchangeable (in sets) with the earlier type and may be used on phase one NTE engines.
Cummins has not changed its recommended injector service interval, which already stands at a generous 290,000km (180,000 miles) for injector cleaning and calibration but operators should find the new injectors need very little attention at this mileage. Significantly extended life for the injector cam followers is promised now that they have a crowned profile.
For the Super E 320 and 350 models only, Cummins has extended its recommended oil change interval from 16,000km to 25,000km. "Caution" is again given as Cummins's reason for not extending drain periods on the more powerful engines. All four new 14-litre variants have a more efficient two-pass oil cooler, spin-on full flow and by-pass oil filters and a sump capacity increased from 32 to 411it (7 to 9gallon ).
But because the latest by-pass filter has a smaller capacity than its predecessor, the amount of oil circulating in the engine is virtually unchanged. Thermostatic control of the oil flow through the oil cooler, which was tried experimentally on some phase one NTE engines, is now a standard feature as is an oil pressure control system which Cummins calls DFC Idemand flow cooling).
This involves sensing oil pressure as close as possible to the crankshaft main bearings as well as fitting a conventional pressure relief valve at the pump. The objective is to have closer control over engine oil temperature and pressure, thereby reducing the power requirement of the oil pump.
Another feature of the latest Cummins lubrication system is a two-stage oil pressure warning system, with one sensor for low pressure and another to sense the differential pressure across the filter.
All Super E Series variants are fitted with Holset's latest H3B turbocharger.
It seems likely that the extra cost of the Super E320 to the operator compared with an NTE 290 will be only about £300. It is also beginning to become clear what some chassis manufacturers' policies regarding fitment of the latest Cummins engines will be. Bedford has no plans to fit Super E engines and will continue to use phase one NTE models. The cost of type approval of Super E-powered TMs weighed against the low volume of TM sales appears to be Bedford's main reason for this policy.
As for the LTA10-290, Bedford is reported to be looking at it but with no firm plans as yet to use it.
ERF on the other hand sees the 290hp 10-litre engine as becoming its "mainstream engine" for 4x2 and 6x2 tractive units with the Super E320 on offer for ERF operators "who will always like litres".
Foden will be sticking to its policy of custom building and fitting all four of the Super E variants and the LTA10-290 "if the customers want them."
A.J.A. Smith of Clitheroe will be taking four 6x4 Fodens fitted with Super E 320's.
Now that production of the H Series has ceased, Ford has no chassis which can accept the 14-litre engine and officially it has no plans to fit the LTA10-290, though the L10-powered 34-tonne gcw Cargo tractive unit will be available soon. However, I would not be surprised to see Ford eventually bowing to pressure from customers and dealers and producing a 38-tonne gcw, LTA-290-powered Cargo.
Leyland will be using the Super E320 as its standard engine for the 6x2 Scammell Roadtrain and though no decision has yet been made, it is possible that, when the Rolls-Royce 340 Li becomes available in 4x2 rhd Roadtrains later this year, a Super E Cummins equivalent, perhaps the 350hp model, will become an alternative.
Leyland is evaluating 10-litre Cummins engines, including the LTA-10-290, in wide-C40-cabbed models such as Roadtrain, but has no plans to use this engine in narrow-cabbed models.
Seddon Atkinson will be using the Super E320 in three 401 tractive unit models, a 4x2, a 6x2 and a 6x4, which are not expected to be type approved until the summer. A 6x4 301 tractive unit is also likely to be ready in the summer and that will be fitted with the LTA-10-290, as will a 6x2 and 4x2 301.
What benefits can operators expect from the latest breed of Cummins engines? The performance curves are shown on this week's Engineering News pages. However, Cummins makes it difficult to make meaningful comparisons between the Super E320 and Super E350, for example, by using different scales on the charts. Nevertheless it can be seen that the 320hp rated engine, which will have a typical installed power rating of 304hp, offers potentially very good fuel economy. Its full load specific fuel consumption curve dips as low as 194g/kWh (0.319Ib/hph) and stays below 200g /kWh (0.32016 /hph) between 1,250 and 1,75Orpm.
Compared to the E290 the Super E329 has 18 per cent more maximum torque and torque rise (the difference between torque at maximum power speed and maximum torque) has gone up from 16 per cent to 24 per cent.
For an operator of E290-powered 32 or 38-tonners then, the Super E320 would seem to offer potentially faster journey times and better fuel economy — an unusual combination. It will be interesting to see the results of a CM road test.