Article - Issue 32, Sep 2007

JCB Dieselmax – powering the World's Fastest Diesel Vehicle

David Tremayne

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It was one of the most unusual challenges of recent engineering in the UK. How to turn a humble 140 bhp diesel engine from its usual use, powering a JCB digger, into a 750 bhp racing unit capable of winning a land speed record? David Tremayne, who has reported on many speed record attempts, describes the engineering achievements involved in creating the JCB Dieselmax streamliner.

JCB Dieselmax at 335mph on the Bonneville Salt Flats. After achieving 365mph on the first pass (see above), this effort was enough to give Andy Green and the team an average speed of 350.092mph, thereby setting a new FIA diesel land-speed record

JCB Dieselmax at 335mph on the Bonneville Salt Flats. After achieving 365mph on the first pass (see above), this effort was enough to give Andy Green and the team an average speed of 350.092mph, thereby setting a new FIA diesel land-speed record

Once Sir Anthony Bamford, Chairman of JCB, had set his heart on breaking the land speed record for diesel-powered vehicles, he was adamant about one thing, he wanted to prove the versatility of JCB’s standard 444 engine and to validate it in a totally different and extremely demanding engineering environment. The backhoe digger power unit thus had to be the heart of his team’s car.

‘Visioneering’ were contracted to build the car in Coventry. The former F1 engineer John Piper designed the car, with the crucial aerodynamics handled by Ron Ayers. It was Ayers’s genius that had helped to create ThrustSSC, the world’s only supersonic car. That side of the operation was relatively straightforward.

However, Bamford’s bold requirement posed a phenomenal challenge to the team, led by JCB’s Group Engineering Director Dr Tim Leverton and in particular to ‘Ricardo’, the consultant engineering company whose responsibility it was to develop the power units to enable a project target speed of 350 mph.

Standard specifications

The standard JCB 444 engine met four key design targets: strong construction; high torque at low engine speeds; reduced noise levels; and future-proofing for the next steps in emissions legislations. Also in its favour were a very strong crankshaft, an exceptionally stiff cylinder block and a substantial cast-iron bedplate (the plate at the bottom of the engine, which closes the crankcase and gives it extra rigidity).

The challenge was to multiply the digger engine’s specific power output by a factor of five, since two engines and 1500 bhp were required to hit the target speed of 350 mph. This was exacerbated when Leverton insisted that the engine had to retain the standard block and fundamental architecture: “It had to be recognisably the JCB 444 engine. We ended up with a stock block, with only internal tweaks, cylinder head and bedplate.”

There were further drawbacks. The basic engine weighed 470 kg. With high-powered diesels, the ideal is to have multiple cylinders. This is because the number of injectors dictates how much fuel can be pumped in and thus how much power the engine can generate.

Engine overhaul

The first step was easily achievable – the engine was bored and stroked to five litres. The greatest challenge lay in getting sufficient air and fuel into it to increase power, and then managing that air and fuel flow and the associated heat generated by two-stage turbocharging operating at over 6 bar.

A turbo system with inter-stage and after-cooling was developed in order to deliver the required air flow across the engine speed range. A water injection system provided a further level of charge cooling to protect the pistons and valves. “Getting the fuel and air in was the single most difficult thing as far as I was concerned”, said Matt Beasley, Chief Engineer for the engine on the Dieselmax project. “The fuel system was a big challenge, getting the engine to run the speed we needed to achieve the power we needed.”

The combustion and fuel systems were very much the heart of the engine. Ricardo used its High Speed Diesel Race (HSDR) direct injection combustion technology wherein fuel was delivered via two parallel, high pressure pumps to a common rail system delivering an injection pressure of 1600 bar. The cylinder head had to be modified slightly to encompass the larger injectors required, and the actuation time for each injector was subtly modified.

Customising the pistons

While the valve train was essentially carried over in its original form with the exception of high temperature exhaust valve material and uprated springs, the pistons were totally new with a large, quiescent combustion chamber with reduced compression ratio, and specific features to reduce the risk of thermal damage to the combustion chamber components. Adequate piston cooling was assured by doubling the size of the oil cooling jets and adding more, to increase oil flow for each piston by around 600 per cent.

A completely new, fully machined connecting rod was also incorporated, including a significantly enlarged small-end bearing to increase strength and robustness. While giving a longer stroke, the billet-machined crankshaft was lightened but retained its main and big end bearing sizes and shells.

Power attained

Eighteen months of development yielded impressive results. By July 2006, the engine weight had come down to 375kg. Peak power had risen to 750bhp at 3800rpm (almost twice the standard 444’s rotational speed) and peak torque to 1500Nm. The JCB444 LSR engine therefore generated more than five times the power of the production version and, at 150bhp/litre, exceeded even motorsports applications as the world’s highest specific power diesel car engine.

Initially the engines were run upright on the dynamometer but they would be inclined at 10 degrees from the horizontal in the car, a distinctive 30 foot long, 48 inch-wide, sleak aerodynamic vehicle, known in racing circles as a ‘streamliner’. They were inclined to lower the centre of gravity which in turn would make the vehicle more stable, with a reduced cross-sectional area. Another result of this inclination was increased capacity of the fuel pumps (in upright guise they produced 700 bph) and thus an improvement of power output.

The layout

The JCB Dieselmax streamliner located one engine and transmission ahead of the driver’s cockpit, the other behind it. Apart from the ground, there was no mechanical link between the two, and the gearshifts were synchronised electronically.

“We have talked this through, and so long as the engines are close enough to each other in specific output and run at the same speed, they will regulate themselves mechanically,” Leverton explained. But once the car began running in tests at RAF Wittering in the UK in July, and then on the Bonneville Salt Flats in Utah in August, a significant problem became apparent. Driver Andy Green, who had driven ThrustSSC to its supersonic record of 763.035mph back in October 1997, discovered that while the front engine established boost easily, the rear lagged behind. Each engine needed an exhaust temperature in excess of 400ºC before boost could be sustained.

Last minute hitches

It transpired that the rear unit was merely going along for the ride, acting like a brake! This was a vexing problem, but would prove to be the only unreliability the highly tuned engines displayed. Beasley conceived a balance pipe to act as a mechanical link between the two engines to ensure that the available boost was distributed evenly.

By 17 August things had reached crisis point following another failure of boost despite the balance pipe and Green adopting a technique of dragging the brakes with his left foot in order to give the engines something to work against and increase their working temperature. It then transpired that a software problem had intervened, fooling the rear engine into thinking it was in neutral and therefore only fuelling it to run at 2100 rpm.

With the software problem cured, Green achieved a one-way run at 308.622mph, well over the existing US national record of 300.8mph. The next day, under the rules of Bonneville’s Speed Week, he made his mandatory return run and hit 325.791mph, to set a new SCTA-BNI national average of 317.021mph. That was only the beginning of establishing the JCB Dieselmax’s full potential. Thus far they had only used 600bhp ‘mule’ (test) engines, not the 750bhp ‘race’ units.

Going flat out

Twice the following week, now running under Federation Internationale de l’Automobile (FIA) international sanction and with the ‘race’ engines installed, Green and JCB Dieselmax improved their speed. On 22 August they set a new FIA international diesel record with a speed of 328.767mph and early the following morning Green sped across Bonneville’s white lunar landscape at 365.745mph, and in one jump the magic 350mph goal of the project came into reach.

However, it all nearly went wrong on the return run less than an hour later when the boost problem suddenly recurred as the yellow and black car stammered down the course, eating up precious run-up area at pitiful speed. Then Green coaxed it back on song, and it shot on to the horizon. It remained to be seen just how much damage had been done to the crucial average for the two runs.

The speed for the second run was 335.695mph. The FIA calculates the elapsed times for the measured mile, then divides them and calculates the speed from the result. Green had just done enough. The average speed was 350.092mph!

JCB’s PR team set about communicating the team’s phenomenal success to the world. The project website, which had proved an invaluable tool in keeping the public informed throughout the project, was updated with downloadable images and broadcast news footage. Regular daily blogs from team members that had once expressed frustration now revealed the team’s jubilant and proud spirit at their achievments.

A record breaker

“I’m so pleased that we got the car to what was only ever the maximum aspirational run speed”, said Andy Green, “and that with a problematic start and so much more to come. It was still pulling like a train once I got it going, and I still haven’t used sixth gear! It’s got so much to give, this car. It’s fantastic! Now all we need are new tyres, to make it go a lot faster.”

JCB may yet go back to the Salt in 2008 but regardless of that, the 2006 record success wrote another great chapter in the remarkable story of British engineering in record breaking. It was not motivated merely by corporate vanity; indeed Bamford’s practical desire all along was to prove the quality of his engine and to explore potential developmental avenues for future introduction to his company’s product range. JCB Dieselmax thus marked the first time in many years that a speed project was undertaken for business reasons, and it remains the only time anyone has relied for glory on anything so humble as a digger engine.

Piston and fuel system development

The pistons were always one of the biggest risk areas in the JCB444 LSR engine. Ricardo needed to run the aluminium components at very, very high thermal and mechanical loads, in the sort of extreme circumstances at which the metal normally degrades. But there was no option: the material minimised weight, facilitating an engine speed almost twice the unit’s norm. The associated piston problems were a corollary of the fuel system that was necessary to achieve the high power output.

In a gasoline engine, fuel can easily be used as a coolant. In some high performance turbocharged applications, it is common to alleviate thermal problems by cooling the pistons with fuel spray and enduring the associated high fuel consumption. But in a turbocharged diesel application that would only create smoke.

As Ian Penny explained, “Because of that we inherently run very hot. The old turbocharged Formula One engines were very well engineered, but there wasn’t anything special to stop the pistons melting, just lots of fuel. In a port-injected gasoline engine you inject fuel into the port or manifold over about two or three hundred crank degrees. It evaporates, it gets sucked in, induction, compression, all nicely mixed, spark, burn. We’ve got to inject within about 30 crank degrees, you’ve got to inject the mix and burn it within about 50 crank degrees, that’s what makes it a challenge with the fuel system.

“You need to put an awful lot of fuel in, in a very, very short space of time, and you’ve got to put it through a minute orifice to get the fuel to mix. Diesel fuel is not as prone to mixing as gasoline because it’s a heavy fuel so it doesn’t evaporate, so you don’t have the time to do that and you have to inject it through a tiny pinprick hole at massive pressure in a tiny space of time. That’s why the fuel system on any diesel engine is a major challenge.”

JCB invested huge effort to create reliable components, as the bore ‘pick up’ problems continued. With the original 108 mm piston design the upright engine achieved almost 700 bhp (680) in December 2005. However as the inclined engine switched to a 109 mm Federal Mogul piston in February 2006, the problems really began and the focus of troubleshooting became the brand new dry-sump lubrication system and its oil scavenging shortfall. There was so much oil flow because, in order to control the piston, there had to be a six-time increase in its oil cooling.

“You have got oil spraying the underside of the piston which then just creates a big foaming mess, so there is an awful lot of oil flow and 6 bar boost,” continued Penny. “That means there is a huge amount of gas flow through the engine and latterly you get blow-by into the crankcase, so in terms of managing the dry sump system you have got an awful lot of oil and air flow to control.”

Green spin-offs

Ricardo’s Global Director of Diesel Engineering, Ian Penny, was proud of the engine’s ecological credentials. “It runs a very low compression ratio, which brings the pressure and temperature down. It’s 10.5 to 1, whereas a diesel is normally between 16 and 20 to 1. It’s also got very high charge cooling so that the inlet manifold temperature is 25 to 30 degrees centigrade, and that’s after we have compressed it to six bar. So it’s got very low pressure, very low temperature, it has water injection, which is a fantastic emissions control feature, and it runs a high pre-mix combustion system. This means the kind of combustion we are operating is very much towards the future, low-temperature combustion. In these respects it is a very green engine.”

Biography: David Tremayne

David Tremayne is a freelance motorsport writer who covers the FIA Formula One World Championship for a number of clients, including The Independent and The Independent on Sunday. A prolific author, he wrote the definitive biography of speedking Donald Campbell, and the inside stories of the Thrust2, ThrustSSC and JCB Dieselmax land speed records

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